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polymer matrix composite laminated composites
MATERIALS SCIENCE & ENGINEERING ELSEVIER
Materials Science and Engineering A194 (1995) 157-163
A
Crack propagation behaviour during three-point bending of polymer matrix composite/AlzO3/polymer matrix composite laminated composites S . H . H o n g a, H . Y . K i m a, J . R . L e e b
aDepartment of Materials Science and Engineering, Korea Advanced Institute of Science and Technology, 373-1 Kusung-dong, Yusung-gu, Taejon, South Korea bpolymer Composite Research Laboratory, Korea Research Institute of Chemical Technology, 100 Jang-dong, Yusung-gu, Taejon, South Korea Received 2 May 1994; in revised form 2 August 1994
Abstract The crack propagation behaviour during three-point bending of a monolithic A1203 and PMC/AI2OJPMC (where PMC denotes polymer matrix composite) laminated composites have been investigated. The laminated composites were fabricated by bonding two PMC layers on both sides of an AI203 plate. Carbon-epoxy and aramid-epoxy composites with two different stacking sequences, i.e. carbon(0/90)4 (C(0/90)), carbon( + 4 5 / - 45)4 (C( + 4 5 / - 45)), aramid(0/90)4 (A(0/90)) and aramid( + 4 5 / - 45)4 (A( + 4 5 / - 45)), were laminated with A1203 plate. The total fracture energy of the PMC/AIzO3/PMC laminated composite increased more than two orders of magnitude compared with that of monolithic AI203.The three-point bending process of the PMC/A1203/PMClaminated composite could be divided into three regimes related to the crack initiation and propagation. The PMC/AIzO3/PMC laminated composite deformed elastically in regime I. A crack was initiated and opened in the A1203 layer in regime II, and the outer PMC layer were deformed without complete debonding at A1203-PMC interface in regime III. The crack initiation stress at AI203 layer is proportional to the elastic modulus of PMC and the energy absorbed in regime I is the energy for elastic deformation of PMC/AIzO3/PMC laminated composites. The C(0/90)/A1203/C(0/90 ) and A(O/90)/A1203/A(O/90) composites, in which the laminated PMCs have higher flexural stress and modulus, fractured by the debonding at the AI203-PMC interface. The C( + 4 5 / - 45)/A1203/C ( + 4 5 / - 45) and A( +45/- 45)/A1203A( + 4 5 / - 4 5 ) composites, in which the laminated PMCs have lower flexural stress and modulus, did not debond at the A1203-PMC interface but fractured by the deformation of PMC layer.
Keywords: Cracking; Aluminium; Oxygen; Composites; Polymers; Laminates
1. Introduction Ceramic materials are attractive for their excellent resistance to heat and wear with high specific strength and good oxidation resistance. However, the major problem of using ceramics as structural materials is their inherent brittleness. T h e r e have been many studies on ceramic matrix composites in order to enhance the toughness through composite toughening by the addition of reinforcements. Two different kinds of ceramic matrix composites have been focused on. Firstly, the fibre-reinforced ceramic matrix composites, such as S i C - A I 2 0 3 [1], SiC-Si3N 4 [2], C - A 1 2 0 3 [3], SiC-glass [4] and C-glass [5], exhibited much better
fracture toughness than monolithic ceramics. Various toughening mechanisms in ceramic matrix composites are suggested such as crack deflection [6], fibre pull-out [7], fibre bridging [8] and matrix microcracking [9], which are dependent on the composite systems. Secondly, it is reported that the laminated composites displayed a much enhanced fracture toughness. Clegg et al. [10] reported that the fracture energy is measured as 6 kJ m-2 in SiC/SiC laminated composite compared with 28 J m-2 in monolithic SiC. T h e enhancement of the fracture toughness in laminated composites is known to be related to the crack deflection at the interfaces [11]. It is also reported that the fracture toughness of metallic glass/brass laminated composites increased
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considerably compared with the monolithic metallic glass [12,13]. The toughening mechanism of a metal/ ceramic laminated composite is known to be related to the crack tip shielding caused by the ductile phase and the crack deflection at the ceramic-metal interface
[a3]. In this study, the crack propagation behaviour during three-point bending of a monolithic A1203 specimen and PMC/AlzO3/PMC (where PMC denotes polymer matrix composite) laminated composite were investigated. The laminated composites were fabricated by bonding two PMC layers on both sides of an AI203 plate. Four different laminated composites, C(0/90)/A1203/C(0/90), C( + 4 5 / - 4 5 ) / A1203/C(+45/-45), A(O/90)/AI203/A(O/90 ) and A( +45/-45)/AI203/A( + 4 5 / - 4 5 ) , where C(0/90) denotes carbon(0/90)4, C(+45/-45) denotes carbon( + 45/-45)4, A(0/90) denotes aramid(0/90)4 and A ( + 4 5 / - 4 5 ) denotes aramid( + 4 5 / - 4 5 ) 4 , were fabricated using two types of prepregs stacked with different sequences. The crack initiation and propagation characteristics in each layer of the PMC/A1203/ PMC laminated composites were investigated during three-point bend tests. The effect of a PMC layer on the crack initiation stress and the crack propagation mode in PMC/A1203/PMC laminated composites was discussed. The effect of the properties of PMC layers on fracture energies of the PMC/AI203/PMC laminated composites was analysed.
2. Experimental details
An epoxy system composed of 100 parts of tetraglycidyl ether of diaminodiphenyl methane (MY720 from Ciba Geigy), 27 parts of 4.4'-diaminodiphenyl sulphone and 1 part of boron trifluoride monoethyl amine was formulated to impregnate fibre mats. Two types of fibre mats, plain woven carbon fabric (6644B from Toray Industries) and plain woven aramid fabric (T240 from Teijin), were used. Four plies of the fabrics were stacked with two different stacking sequences (0/90)4 and ( + 4 5 / - 4 5 ) 4 . The prepregs were cured in an autoclave at 120 °C for 45 min followed by 170 °C for 2 h. The autoclave pressure was maintained at 0.5 MPa during curing. A vacuum bagging procedure was employed to cure the prepregs. PMC/AIzO3/PMC laminated composites were fabricated by bonding two layers of 1.2 mm thick PMCs on both sides of 3.8 mm thick A1203 plate using an adhesive (American Cyanamid FM123-2). Sintered AI203 plates with purity of 98.5% were used. The cure condition used to bond PMC with A120 3 plate was 80°C for 30 rain followed by 150°C for 3 h in an autoclave. Four different laminated composites
C(0/90)/A1203/C(0/90), C( + 4 5 / - 45)/A1203/C ( + 45/ -45), A(0/90)AI203/(0/90 ) and A ( + 4 5 / - 4 5 ) / A1203/A ( + 4 5 / - 4 5 ) were fabricated. The notation C means the carbon fibre reinforced PMC and notation A means the aramid fibre reinforced PMC. Three-point bend tests were carried out for PMCs, monolithic AI203 and PMC/AlzO3/PMC laminated composites using an Instron tensile testing machine with a constant cross-head speed of 1 mm min- 1 to the crack arrest direction. The dimensions of three-point bending specimens were 10 mm wide, 50 mm long and 1.2 mm thick for the PMCs, 10 mm wide, 50 mm long and 3.8 mm thick for the monolithic AI203 and 10 mm wide, 50 mm long and 6.5 mm thick for the PMC/ A1203/PMC composites.
3. Results and discussion
The stress-strain curves obtained from the threepoint bend tests of the monolithic Al203 and PMC/ A1203/PMC laminated composites are shown in Fig. 1. The monolithic A1203 was deformed elastically to a maximum stress (flexural strength) and then fractured catastrophically as shown in Fig. l(a). The laminated composites exhibited an increased maximum stress and ductility, which resulted in a marked increase in the fracture toughness. Figs. l(b)-l(e) show the threepoint bending behaviour of the PMC/AI203/PMC laminated composites. The three-point bending behaviour of the PMC/A1203/PMC composites was affected by the type of fibre and the stacking sequences of prepregs in the PMC. The C(0/90)/A1203/C(0/90 ) and A(0/90)/AI203/A(0/90 ) composites exhibited catastrophic stress drop after maximum stress, while a considerable amount of plastic deformation was observed after maximum stress in the C ( + 4 5 / - 4 5 ) A 1 2 0 3 / C ( + 4 5 / - 4 5 ) and A ( + 4 5 / - 4 5 ) / A I 2 0 3 / A( + 4 5 / - 45) composites. The elastic modulus and the flexural strength of A1203 and PMCs measured by three-point bend tests are listed in Table 1. Carbon fibre reinforced PMCs have a higher elastic modulus and flexural strength than aramid fibre reinforced PMCs. The elastic modulus and flexural strength of (0/90) lay-up PMCs are higher than those of ( + 4 5 / - 45) lay-up PMCs. The crack propagation behaviour in the PMC/ AIzO3/PMC laminated composites during the threepoint bend tests is shown in Fig. 2. The crack propagation in the PMC/AIzO3/PMC laminated composites was sensitively affected by the characteristics of the PMC. A crack was initiated and propagated in the A1203 layer initially, and then followed by AI203-PMC interface debonding and plastic deformation of the PMC layer when the crack reached an
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Fig. 1. The stress-strain curves obtained from three-point bend tests of a monolithic A1203 and PMC/A1203/PMC laminated composites: (a) monolithic A1203; (b) C(0/90)/A1203/C(0/90); (c)C( +45/-45)/A1203/C ( + 4 5 / - 4 5 ) ; (d) A(0/90)/AI203/A(0/90); (e) A( + 4 5 / - 45)/A1203/A(+45/-45).
Table 1 The flexural moduli and flexural strengths measured by the three point bend tests of a monolithic AI203 and four types of polymer matrix composites Material
E (GPa)
a (MPa)
AI203 Carbon(0/90) 4 Carbon( +45/-45)4 Aramid(0/90)4 Aramid( +45/-45)4
62 23 10 14 5
143 360 220 240 150
AI203-PMC interface. The A1203-PMC interface debonding was much more dominant in C(0/90)/ A1203/C(0/90) and A(0/90)/A1203/A(0/90) composites. The plastic deformation of the PMC layer was more dominant in C( + 4 5 / - 4 5 ) / A 1 2 0 3 / C ( + 4 5 / - 4 5 ) and A( + 4 5 / - 45)/AlzO3/A ( + 45 / - 45) composites. Comparing the stress-strain curves with the crack propagation behaviour of laminated composites, the three-point bending process is divided into three regimes based on the crack propagation behaviour as shown in Fig. 1. In regime I from the start point to point A, the stress increased linearly with strain until the first load drop at point A and thus all the PMC/
AlzO3/PMC laminated composites deformed elastically in regime I. The load drop at point A is related to the crack initiation in the A1203 layer of the PMC/ AI203/PMC laminated composite. The strain to the first load drop at point A was identical; however, the stress at point A was dependent on the properties of the PMC as shown in Figs. l(b)-l(e). The monolithic A1203 fractured catastrophically after crack initiation, and the crack initiated in the A1203 layer of the PMC/AlzO3/PMC laminated composite was opened slowly in regime II from point A to point B in Fig. 1. In regime II, the PMC layers were deformed elastically and the crack was opened in A1203 layer of the laminated composites. The crack opening in the AlzO3 layer was suppressed by the PMC layers laminated on both sides of the A1203 plate. The stress increased with strain until the second stress drop at point B, which is related to the crack initiation in the PMC layer or debonding at the AI203-PMC interface. The C(0/90)/A1203/C(0/90 ) and A(0/90)/AI20 fl A(0/90) composites, in which the laminated PMC has higher flexural stress and modulus, fractured at point B by debonding at the A1203-PMC interface, while the C ( + 4 5 / - 4 5 ) / A 1 2 0 3 / C ( + 4 5 / - 4 5 ) and A ( + 4 5 / -45)/A1203/A ( + 4 5 / - 4 5 ) composites, in which the laminated PMC has lower flexural stress and modulus,
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Fig. 2. The crack initiation and propagation processes during three-point bend tests of PMC/AI203/PMC laminated composites: (a) C(0/90)/A120~/C(0/90); (b) C( + 4 5 / - 45)/A1203/C( +45/-45); (c)A(0/90)/AI2O3/A(0/90); (d) A( + 4 5 / - 45)/AI203/A(+45/-45).
did not fracture at the AI203-PMC interface but exhibited deformation of the PMC layer. Regime Ill from point B to point C in Fig. l(c) and Fig. l(e) is related to the deformation of the outer PMC layer without complete debonding at A1203/PMC interface. It is suggested that the C(0/90)/A1203/C(0/90 ) and A(0/90)/AI203/A(0/90 ) laminated composites failed at the A1203-PMC interface, since the ratio of flexural strength to tensile stress in the PMC layer is higher than the ratio of interfacial strength to shear stress at the AI203-PMC interface. The C( + 4 5 / - 4 5 ) / A 1 2 0 3 / C ( + 4 5 / - 4 5 ) and A( + 4 5 / - 4 5 ) / A 1 2 0 3 / A ( + 4 5 / - 4 5 ) laminated composites fractured at the PMC layer, since the ratio of flexural strength to tensile stress in the PMC layer is lower than the ratio of interracial strength to shear stress at the AI203-PMC interface. The three-point bending behaviours of the PMC/ A1203/PMC laminated composites in regime I were similar, but the peak stress and modulus were depen-
dent on the properties of the PMC layers. The PMC/ A1203/PMC laminated composites deformed elastically until a crack was initiated at point A, and thus the first peak stress at point A is related to the elastic modulus of the PMC/AlzO3/PMC laminated composites. The energy absorbed up to point A is the elastic deformation energy of the PMC/AlzO3/PMC laminated composites. The peak stress at point A and the elastic modulus of PMC in the P M C / A I 2 0 3 / P M C laminated composites are plotted in Fig. 3. Fig. 3 shows that the peak stress at point A is directly proportional to the elastic modulus of PMC. This result indicates that the stress for crack initiation in the A1203 layer is dependent on the elastic modulus of the laminated composite which is related to the elastic modulus of PMC. In regime II, the peak stress at point B was dependent on the interfacial strength at the A1203-PMC interface and the flexural strength of the PMC. The
S.H, Hong et al.
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Materials Science and Engineering A194 (1995) 157-163
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peak stress at point B was determined by the interracial strength of AlzO3-PMC interface in the C(0/90)/ A1203/C(0/90 ) and A(0/90)/AlzO3/A(0/90 ) laminated composites which fractured by debonding at A1203PMC interface. While the peak stress at point B is determined by the flexural strength of the PMC in the C( + 4 5 / - 45)/A1203/C(+45/-45) and A( + 4 5 / 45)/A1203/A( + 4 5 / - 45) laminated composites which fractured by crack propagation into the outer PMC layer. The tensile stress and shear stress at the AIzO3-PMC interface during three-point bend test are calculated from the following equations: -
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Fig. 4. The schematic representation of two different fracture modes during three-point bend tests of PMC/AI203/PMC laminated composites: (a) drawing of three-point bending specimen showing the tensile stress ot at the PMC layer and the shear stress r~ at A1203-PMC interface induced by aplied load P; (b) stress-load curve showing the interface debonding when the flexural strength is higher than the critical tensile stress; (c) stress-load curve showing the fracture of the PMC layer when flexural strength is lower than the critical tensile stress.
The measured peak stress and shear stress at point B are listed in Table 2. The interracial strength of the A1203-PMC interface is considered constant because of identical adhesive bonding of laminated composites, while the flexural strength depends on the type of PMC layer. If the flexural strength ov of the PMC was higher than the critical tensile stress 0 c which corresponds to the tensile stress when the shear stress ri increased to the interracial strength r c at AI203-PMC interface, the fracture proceeds by debonding at the A1203-PMC interface in the case of the C(0/90)/A1203/C(0/90 ) and A(0/90)/AI203/A(0/90) laminated composites as shown in Fig. 4(b). Then the tensile stress at point B will be close to the critical tensile stress oc and the shear stress ri will be close to the interracial strength r c at the AIzO3-PMC interface in C(0/90)/A1203/ C(0/90) and A(0/90)/AI203/A(0/90) laminated composites. This explanation is strongly supported by the similar tensile stresses and shear stresses measured in C(0/90)/A1203/C(0/90) and A(0/90)/AI203/A(0/90 ) laminated composites, which were fractured by debonding at the A1203-PMC interface, as shown in Table 2. Thus, it is considered that the interracial strength at the AlzO3-PMC interface is about 32-36 MPa and the critical tensile stress is about 220-240 MPa from the measured shear stress and tensile stress in Table 2. On the contrary, if the flexural strength of PMC was lower than the critical tensile stress, the
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Table 2 The tensile stresses at the outer polymer matrix composite layer and the shear stresses at AI203-PMC interface of PMC/AI203/PMC laminated composites at the point B in stress-strain curves in Fig. 1
C(0/90)/A1203/C(0/90) C( + 45/- 45)/A1203/C( + 45/-- 45)
A(O/90)/AI203/A(0/90) A( + 45/- 45)/AI203/A( + 45/- 45)
oB(MPa)
rB (MPa)
Fracture mode
243 141 215 96
36 24 32 14
Interface debonding Fracture of PMC layer Interface debonding Fracture of PMC layer
tensile stress in the PMC layer increased to the flexural strength before the shear stress reached the interfacial shear strength. Then the tensile stresses at point B of C(0/90)/A1~03/C(0/90) and A(O/90)/AlzO3/A(O/90 ) laminated composites, in which the PMC layers fractured, are lower than the critical tensile stress as shown in Table 2. The peak stress at point B is proportional to the flexural strength of the PMC layer in the case of the C( +45/-45)/A1203/C ( + 4 5 / - 4 5 ) and A( + 4 5 / - 4 5 ) / A I 2 0 3 / A ( + 4 5 / - 4 5 ) laminated composites. This is supported by the fact that the ratio between tensile stresses at point B is almost the same as the ratio of flexural strengths of C(0/90)/A1203/C(0/90) to those of A(0/90)/AIzO3/A(0/90) from Table 2 and Table 1. The total energy for the three-point bending of PMC/AI203/PMC laminated composite is the sum of energies absorbed in regimes I, II and III, and the energies calculated in each regime of four different laminated composites are listed in Table 3. The energy in regime I was found to be proportional to the elastic modulus of the PMC. The reason is that the elastic deformation energy of the PMC/A1203/PMC laminated composites is the sum of elastic deformation energies of the PMC layers and the AI203 layer, but the elastic deformation energy of the A1203 layer is negligible compared with that of PMC. The energy in regime II was found to be related to the fracture mode of the PMC/AIzO3/PMC laminated composite. The energy in regime II was proportional to the strength of the PMC layer in the C ( + 4 5 / - 4 5 ) / A 1 2 0 3 / C ( + 4 5 / - 4 5 ) and A( + 4 5 / - 4 5 ) / A I 2 0 3 / A ( + 4 5 / - 4 5 ) laminated composites, which was fractured by the deformation of the PMC layer, while the energy in regime II was inversely proportional to the elastic modulus of PMC in the C(0/90)/A1203/C(0/90) and A(0/90)/A1203/A(0/90) laminated composites as shown in Table 1 and Table 3. The reason is that the energy in regime II is the elastic deformation energy of the PMC layer, which is defined as o2/2E, since the critical tensile stress is constant in the C(0/90)/A1203/ C(0/90) and A(0/90)/AI203/A(0/90) laminated composites. The energy in regime III was proportional to the fracture toughness of the outer PMC layer, because the energy absorption is entirely related to the fracture
Table 3 The energies absorbed in each regime during three-point bending of a monolithic AlzO3 and PMC/AleO3/PMClaminated composites Energies (kJ m -2)
El AI203
C(0/90)/A1203/C(0/90)
C( +45/- 45)/A1203/C(+45/-45)
A(O/90)/A1203/A(O/90) A( + 4 5 / - 45)/AI203/A(+45/-45)
Eli
EIII
13.5 7.4 25.2 5.5
0.2 21.0 1.2 > 30.0
0.5
1.4 1.0 1.1 0.9
of the outer PMC layer. As a result, the PMC with high elastic modulus is effective in suppressing the crack initiation at the A1203 layer in regime I of the PMC/ AI203/PMC laminated composite, while the PMC with high flexural strength with high fracture toughness is effective in enhancing the fracture resistance of the PMC/A1203/PMC laminated composite.
4. Conclusions
The crack propagation behaviour during three-point bending of a monolithic A1203 and PMC/AI203/PMC composites laminated with four diffrent PMCs has been investigated. The fracture behaviour of the PMC/ A1203/PMC laminated composites was sensitively affected by the properties of the PMCs. The total fracture energy of the PMC/AI203/PMC laminated composite increased by more than two orders of magnitude compared with that of monolithic AI203. The three-point bending process of the PMC/AI203/PMC laminated composite was divided into three regions (I, II, III) related to the crack initiation and propagation. In regime I, the PMC/AI203/PMC composite deformed elastically. In regime II, the PMC layers deformed elastically and the crack was initiated and opened in the AI2 03 layer. The crack initiation stress in the A1203 layer is proportional to the elastic modulus of the PMC. In regime III, the PMC/A1203/PMC lami-
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nated composites were fractured by debonding at the A1203-PMC interface in C ( 0 / 9 0 ) / A 1 2 0 3 / C ( 0 / 9 0 ) and A(0/90)/AI203/A(0/90 ) laminated composites, while the outer PMC layers were deformed without complete debonding at the AI203-PMC interface in C( + 4 5 / - 4 5 ) / A1203/C ( + 4 5 / - 4 5 ) and A( + 4 5 / - 45)/A1203/ A(+45/-45) laminated composites. The fracture modes of P M C / A I 2 0 3 / P M C laminated composites were determined by the ratio of flexural strength of PMC to interfacial strength at the A1203-PMC interface.
[3] R.A.J. Sambell, D.H. Bowen and D,C. Phillips, J. Mater. Sci., 7(1972) 663. [4] K.M. Prewo and J.J. Brennan, J. Mater. Sci., 17 (1982) 1201. [5] D.H. Bowen, D.C. Phillips, R.A.J. Sambell and A. Briggs, in Proc. Int. Conf. on the Mechanical Properties of Materials,
[6] [7] [8] [9] [10]
References [1] RE Becher and G.C. Wei, J. Am. Ceram. Soc., 67 (1984) 298. [2] R.W. Rice, Ceram. Eng. Sci. Proc., 2 (1981) 661.
163
[11] [12] [13]
Society of Metals, Japan, 1972, p. 123. K.T.Faber and A.G. Evans, A cta Metall., 31 ( 1983 ) 565. M.D. Thouless and A.G. Evans, Acta Metall., 36 (1988) 517. A.G. Evans and R.M. Mcmeeking, Acta Metall., 34 (1986) 2435. A.G. Evans and K.T. Faber, J. Am. Ceram. Soc., 67(1984) 255. W.J. Clegg, K. Kendall, N. McN. Alford, T.W. Button and J.D. Birchall, Nature (London), 347 (1990) 455. A.J. Phillips, W.J. Clegg and T.W. Clyne, Composites, 24 (1993) 166. Y, Leng and T.H. Courtney, J. Mater. Sci., 24 (1989) 2006. Y. Leng and T.H. Courtney, Metall. Trans. A, 21 (1990) 2159.
Materials Science and Engineering A194 (1995) 157-163
A
Crack propagation behaviour during three-point bending of polymer matrix composite/AlzO3/polymer matrix composite laminated composites S . H . H o n g a, H . Y . K i m a, J . R . L e e b
aDepartment of Materials Science and Engineering, Korea Advanced Institute of Science and Technology, 373-1 Kusung-dong, Yusung-gu, Taejon, South Korea bpolymer Composite Research Laboratory, Korea Research Institute of Chemical Technology, 100 Jang-dong, Yusung-gu, Taejon, South Korea Received 2 May 1994; in revised form 2 August 1994
Abstract The crack propagation behaviour during three-point bending of a monolithic A1203 and PMC/AI2OJPMC (where PMC denotes polymer matrix composite) laminated composites have been investigated. The laminated composites were fabricated by bonding two PMC layers on both sides of an AI203 plate. Carbon-epoxy and aramid-epoxy composites with two different stacking sequences, i.e. carbon(0/90)4 (C(0/90)), carbon( + 4 5 / - 45)4 (C( + 4 5 / - 45)), aramid(0/90)4 (A(0/90)) and aramid( + 4 5 / - 45)4 (A( + 4 5 / - 45)), were laminated with A1203 plate. The total fracture energy of the PMC/AIzO3/PMC laminated composite increased more than two orders of magnitude compared with that of monolithic AI203.The three-point bending process of the PMC/A1203/PMClaminated composite could be divided into three regimes related to the crack initiation and propagation. The PMC/AIzO3/PMC laminated composite deformed elastically in regime I. A crack was initiated and opened in the A1203 layer in regime II, and the outer PMC layer were deformed without complete debonding at A1203-PMC interface in regime III. The crack initiation stress at AI203 layer is proportional to the elastic modulus of PMC and the energy absorbed in regime I is the energy for elastic deformation of PMC/AIzO3/PMC laminated composites. The C(0/90)/A1203/C(0/90 ) and A(O/90)/A1203/A(O/90) composites, in which the laminated PMCs have higher flexural stress and modulus, fractured by the debonding at the AI203-PMC interface. The C( + 4 5 / - 45)/A1203/C ( + 4 5 / - 45) and A( +45/- 45)/A1203A( + 4 5 / - 4 5 ) composites, in which the laminated PMCs have lower flexural stress and modulus, did not debond at the A1203-PMC interface but fractured by the deformation of PMC layer.
Keywords: Cracking; Aluminium; Oxygen; Composites; Polymers; Laminates
1. Introduction Ceramic materials are attractive for their excellent resistance to heat and wear with high specific strength and good oxidation resistance. However, the major problem of using ceramics as structural materials is their inherent brittleness. T h e r e have been many studies on ceramic matrix composites in order to enhance the toughness through composite toughening by the addition of reinforcements. Two different kinds of ceramic matrix composites have been focused on. Firstly, the fibre-reinforced ceramic matrix composites, such as S i C - A I 2 0 3 [1], SiC-Si3N 4 [2], C - A 1 2 0 3 [3], SiC-glass [4] and C-glass [5], exhibited much better
fracture toughness than monolithic ceramics. Various toughening mechanisms in ceramic matrix composites are suggested such as crack deflection [6], fibre pull-out [7], fibre bridging [8] and matrix microcracking [9], which are dependent on the composite systems. Secondly, it is reported that the laminated composites displayed a much enhanced fracture toughness. Clegg et al. [10] reported that the fracture energy is measured as 6 kJ m-2 in SiC/SiC laminated composite compared with 28 J m-2 in monolithic SiC. T h e enhancement of the fracture toughness in laminated composites is known to be related to the crack deflection at the interfaces [11]. It is also reported that the fracture toughness of metallic glass/brass laminated composites increased
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considerably compared with the monolithic metallic glass [12,13]. The toughening mechanism of a metal/ ceramic laminated composite is known to be related to the crack tip shielding caused by the ductile phase and the crack deflection at the ceramic-metal interface
[a3]. In this study, the crack propagation behaviour during three-point bending of a monolithic A1203 specimen and PMC/AlzO3/PMC (where PMC denotes polymer matrix composite) laminated composite were investigated. The laminated composites were fabricated by bonding two PMC layers on both sides of an AI203 plate. Four different laminated composites, C(0/90)/A1203/C(0/90), C( + 4 5 / - 4 5 ) / A1203/C(+45/-45), A(O/90)/AI203/A(O/90 ) and A( +45/-45)/AI203/A( + 4 5 / - 4 5 ) , where C(0/90) denotes carbon(0/90)4, C(+45/-45) denotes carbon( + 45/-45)4, A(0/90) denotes aramid(0/90)4 and A ( + 4 5 / - 4 5 ) denotes aramid( + 4 5 / - 4 5 ) 4 , were fabricated using two types of prepregs stacked with different sequences. The crack initiation and propagation characteristics in each layer of the PMC/A1203/ PMC laminated composites were investigated during three-point bend tests. The effect of a PMC layer on the crack initiation stress and the crack propagation mode in PMC/A1203/PMC laminated composites was discussed. The effect of the properties of PMC layers on fracture energies of the PMC/AI203/PMC laminated composites was analysed.
2. Experimental details
An epoxy system composed of 100 parts of tetraglycidyl ether of diaminodiphenyl methane (MY720 from Ciba Geigy), 27 parts of 4.4'-diaminodiphenyl sulphone and 1 part of boron trifluoride monoethyl amine was formulated to impregnate fibre mats. Two types of fibre mats, plain woven carbon fabric (6644B from Toray Industries) and plain woven aramid fabric (T240 from Teijin), were used. Four plies of the fabrics were stacked with two different stacking sequences (0/90)4 and ( + 4 5 / - 4 5 ) 4 . The prepregs were cured in an autoclave at 120 °C for 45 min followed by 170 °C for 2 h. The autoclave pressure was maintained at 0.5 MPa during curing. A vacuum bagging procedure was employed to cure the prepregs. PMC/AIzO3/PMC laminated composites were fabricated by bonding two layers of 1.2 mm thick PMCs on both sides of 3.8 mm thick A1203 plate using an adhesive (American Cyanamid FM123-2). Sintered AI203 plates with purity of 98.5% were used. The cure condition used to bond PMC with A120 3 plate was 80°C for 30 rain followed by 150°C for 3 h in an autoclave. Four different laminated composites
C(0/90)/A1203/C(0/90), C( + 4 5 / - 45)/A1203/C ( + 45/ -45), A(0/90)AI203/(0/90 ) and A ( + 4 5 / - 4 5 ) / A1203/A ( + 4 5 / - 4 5 ) were fabricated. The notation C means the carbon fibre reinforced PMC and notation A means the aramid fibre reinforced PMC. Three-point bend tests were carried out for PMCs, monolithic AI203 and PMC/AlzO3/PMC laminated composites using an Instron tensile testing machine with a constant cross-head speed of 1 mm min- 1 to the crack arrest direction. The dimensions of three-point bending specimens were 10 mm wide, 50 mm long and 1.2 mm thick for the PMCs, 10 mm wide, 50 mm long and 3.8 mm thick for the monolithic AI203 and 10 mm wide, 50 mm long and 6.5 mm thick for the PMC/ A1203/PMC composites.
3. Results and discussion
The stress-strain curves obtained from the threepoint bend tests of the monolithic Al203 and PMC/ A1203/PMC laminated composites are shown in Fig. 1. The monolithic A1203 was deformed elastically to a maximum stress (flexural strength) and then fractured catastrophically as shown in Fig. l(a). The laminated composites exhibited an increased maximum stress and ductility, which resulted in a marked increase in the fracture toughness. Figs. l(b)-l(e) show the threepoint bending behaviour of the PMC/AI203/PMC laminated composites. The three-point bending behaviour of the PMC/A1203/PMC composites was affected by the type of fibre and the stacking sequences of prepregs in the PMC. The C(0/90)/A1203/C(0/90 ) and A(0/90)/AI203/A(0/90 ) composites exhibited catastrophic stress drop after maximum stress, while a considerable amount of plastic deformation was observed after maximum stress in the C ( + 4 5 / - 4 5 ) A 1 2 0 3 / C ( + 4 5 / - 4 5 ) and A ( + 4 5 / - 4 5 ) / A I 2 0 3 / A( + 4 5 / - 45) composites. The elastic modulus and the flexural strength of A1203 and PMCs measured by three-point bend tests are listed in Table 1. Carbon fibre reinforced PMCs have a higher elastic modulus and flexural strength than aramid fibre reinforced PMCs. The elastic modulus and flexural strength of (0/90) lay-up PMCs are higher than those of ( + 4 5 / - 45) lay-up PMCs. The crack propagation behaviour in the PMC/ AIzO3/PMC laminated composites during the threepoint bend tests is shown in Fig. 2. The crack propagation in the PMC/AIzO3/PMC laminated composites was sensitively affected by the characteristics of the PMC. A crack was initiated and propagated in the A1203 layer initially, and then followed by AI203-PMC interface debonding and plastic deformation of the PMC layer when the crack reached an
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Fig. 1. The stress-strain curves obtained from three-point bend tests of a monolithic A1203 and PMC/A1203/PMC laminated composites: (a) monolithic A1203; (b) C(0/90)/A1203/C(0/90); (c)C( +45/-45)/A1203/C ( + 4 5 / - 4 5 ) ; (d) A(0/90)/AI203/A(0/90); (e) A( + 4 5 / - 45)/A1203/A(+45/-45).
Table 1 The flexural moduli and flexural strengths measured by the three point bend tests of a monolithic AI203 and four types of polymer matrix composites Material
E (GPa)
a (MPa)
AI203 Carbon(0/90) 4 Carbon( +45/-45)4 Aramid(0/90)4 Aramid( +45/-45)4
62 23 10 14 5
143 360 220 240 150
AI203-PMC interface. The A1203-PMC interface debonding was much more dominant in C(0/90)/ A1203/C(0/90) and A(0/90)/A1203/A(0/90) composites. The plastic deformation of the PMC layer was more dominant in C( + 4 5 / - 4 5 ) / A 1 2 0 3 / C ( + 4 5 / - 4 5 ) and A( + 4 5 / - 45)/AlzO3/A ( + 45 / - 45) composites. Comparing the stress-strain curves with the crack propagation behaviour of laminated composites, the three-point bending process is divided into three regimes based on the crack propagation behaviour as shown in Fig. 1. In regime I from the start point to point A, the stress increased linearly with strain until the first load drop at point A and thus all the PMC/
AlzO3/PMC laminated composites deformed elastically in regime I. The load drop at point A is related to the crack initiation in the A1203 layer of the PMC/ AI203/PMC laminated composite. The strain to the first load drop at point A was identical; however, the stress at point A was dependent on the properties of the PMC as shown in Figs. l(b)-l(e). The monolithic A1203 fractured catastrophically after crack initiation, and the crack initiated in the A1203 layer of the PMC/AlzO3/PMC laminated composite was opened slowly in regime II from point A to point B in Fig. 1. In regime II, the PMC layers were deformed elastically and the crack was opened in A1203 layer of the laminated composites. The crack opening in the AlzO3 layer was suppressed by the PMC layers laminated on both sides of the A1203 plate. The stress increased with strain until the second stress drop at point B, which is related to the crack initiation in the PMC layer or debonding at the AI203-PMC interface. The C(0/90)/A1203/C(0/90 ) and A(0/90)/AI20 fl A(0/90) composites, in which the laminated PMC has higher flexural stress and modulus, fractured at point B by debonding at the A1203-PMC interface, while the C ( + 4 5 / - 4 5 ) / A 1 2 0 3 / C ( + 4 5 / - 4 5 ) and A ( + 4 5 / -45)/A1203/A ( + 4 5 / - 4 5 ) composites, in which the laminated PMC has lower flexural stress and modulus,
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Fig. 2. The crack initiation and propagation processes during three-point bend tests of PMC/AI203/PMC laminated composites: (a) C(0/90)/A120~/C(0/90); (b) C( + 4 5 / - 45)/A1203/C( +45/-45); (c)A(0/90)/AI2O3/A(0/90); (d) A( + 4 5 / - 45)/AI203/A(+45/-45).
did not fracture at the AI203-PMC interface but exhibited deformation of the PMC layer. Regime Ill from point B to point C in Fig. l(c) and Fig. l(e) is related to the deformation of the outer PMC layer without complete debonding at A1203/PMC interface. It is suggested that the C(0/90)/A1203/C(0/90 ) and A(0/90)/AI203/A(0/90 ) laminated composites failed at the A1203-PMC interface, since the ratio of flexural strength to tensile stress in the PMC layer is higher than the ratio of interfacial strength to shear stress at the AI203-PMC interface. The C( + 4 5 / - 4 5 ) / A 1 2 0 3 / C ( + 4 5 / - 4 5 ) and A( + 4 5 / - 4 5 ) / A 1 2 0 3 / A ( + 4 5 / - 4 5 ) laminated composites fractured at the PMC layer, since the ratio of flexural strength to tensile stress in the PMC layer is lower than the ratio of interracial strength to shear stress at the AI203-PMC interface. The three-point bending behaviours of the PMC/ A1203/PMC laminated composites in regime I were similar, but the peak stress and modulus were depen-
dent on the properties of the PMC layers. The PMC/ A1203/PMC laminated composites deformed elastically until a crack was initiated at point A, and thus the first peak stress at point A is related to the elastic modulus of the PMC/AlzO3/PMC laminated composites. The energy absorbed up to point A is the elastic deformation energy of the PMC/AlzO3/PMC laminated composites. The peak stress at point A and the elastic modulus of PMC in the P M C / A I 2 0 3 / P M C laminated composites are plotted in Fig. 3. Fig. 3 shows that the peak stress at point A is directly proportional to the elastic modulus of PMC. This result indicates that the stress for crack initiation in the A1203 layer is dependent on the elastic modulus of the laminated composite which is related to the elastic modulus of PMC. In regime II, the peak stress at point B was dependent on the interfacial strength at the A1203-PMC interface and the flexural strength of the PMC. The
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Materials Science and Engineering A194 (1995) 157-163
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peak stress at point B was determined by the interracial strength of AlzO3-PMC interface in the C(0/90)/ A1203/C(0/90 ) and A(0/90)/AlzO3/A(0/90 ) laminated composites which fractured by debonding at A1203PMC interface. While the peak stress at point B is determined by the flexural strength of the PMC in the C( + 4 5 / - 45)/A1203/C(+45/-45) and A( + 4 5 / 45)/A1203/A( + 4 5 / - 45) laminated composites which fractured by crack propagation into the outer PMC layer. The tensile stress and shear stress at the AIzO3-PMC interface during three-point bend test are calculated from the following equations: -
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Fig. 4. The schematic representation of two different fracture modes during three-point bend tests of PMC/AI203/PMC laminated composites: (a) drawing of three-point bending specimen showing the tensile stress ot at the PMC layer and the shear stress r~ at A1203-PMC interface induced by aplied load P; (b) stress-load curve showing the interface debonding when the flexural strength is higher than the critical tensile stress; (c) stress-load curve showing the fracture of the PMC layer when flexural strength is lower than the critical tensile stress.
The measured peak stress and shear stress at point B are listed in Table 2. The interracial strength of the A1203-PMC interface is considered constant because of identical adhesive bonding of laminated composites, while the flexural strength depends on the type of PMC layer. If the flexural strength ov of the PMC was higher than the critical tensile stress 0 c which corresponds to the tensile stress when the shear stress ri increased to the interracial strength r c at AI203-PMC interface, the fracture proceeds by debonding at the A1203-PMC interface in the case of the C(0/90)/A1203/C(0/90 ) and A(0/90)/AI203/A(0/90) laminated composites as shown in Fig. 4(b). Then the tensile stress at point B will be close to the critical tensile stress oc and the shear stress ri will be close to the interracial strength r c at the AIzO3-PMC interface in C(0/90)/A1203/ C(0/90) and A(0/90)/AI203/A(0/90) laminated composites. This explanation is strongly supported by the similar tensile stresses and shear stresses measured in C(0/90)/A1203/C(0/90) and A(0/90)/AI203/A(0/90 ) laminated composites, which were fractured by debonding at the A1203-PMC interface, as shown in Table 2. Thus, it is considered that the interracial strength at the AlzO3-PMC interface is about 32-36 MPa and the critical tensile stress is about 220-240 MPa from the measured shear stress and tensile stress in Table 2. On the contrary, if the flexural strength of PMC was lower than the critical tensile stress, the
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Table 2 The tensile stresses at the outer polymer matrix composite layer and the shear stresses at AI203-PMC interface of PMC/AI203/PMC laminated composites at the point B in stress-strain curves in Fig. 1
C(0/90)/A1203/C(0/90) C( + 45/- 45)/A1203/C( + 45/-- 45)
A(O/90)/AI203/A(0/90) A( + 45/- 45)/AI203/A( + 45/- 45)
oB(MPa)
rB (MPa)
Fracture mode
243 141 215 96
36 24 32 14
Interface debonding Fracture of PMC layer Interface debonding Fracture of PMC layer
tensile stress in the PMC layer increased to the flexural strength before the shear stress reached the interfacial shear strength. Then the tensile stresses at point B of C(0/90)/A1~03/C(0/90) and A(O/90)/AlzO3/A(O/90 ) laminated composites, in which the PMC layers fractured, are lower than the critical tensile stress as shown in Table 2. The peak stress at point B is proportional to the flexural strength of the PMC layer in the case of the C( +45/-45)/A1203/C ( + 4 5 / - 4 5 ) and A( + 4 5 / - 4 5 ) / A I 2 0 3 / A ( + 4 5 / - 4 5 ) laminated composites. This is supported by the fact that the ratio between tensile stresses at point B is almost the same as the ratio of flexural strengths of C(0/90)/A1203/C(0/90) to those of A(0/90)/AIzO3/A(0/90) from Table 2 and Table 1. The total energy for the three-point bending of PMC/AI203/PMC laminated composite is the sum of energies absorbed in regimes I, II and III, and the energies calculated in each regime of four different laminated composites are listed in Table 3. The energy in regime I was found to be proportional to the elastic modulus of the PMC. The reason is that the elastic deformation energy of the PMC/A1203/PMC laminated composites is the sum of elastic deformation energies of the PMC layers and the AI203 layer, but the elastic deformation energy of the A1203 layer is negligible compared with that of PMC. The energy in regime II was found to be related to the fracture mode of the PMC/AIzO3/PMC laminated composite. The energy in regime II was proportional to the strength of the PMC layer in the C ( + 4 5 / - 4 5 ) / A 1 2 0 3 / C ( + 4 5 / - 4 5 ) and A( + 4 5 / - 4 5 ) / A I 2 0 3 / A ( + 4 5 / - 4 5 ) laminated composites, which was fractured by the deformation of the PMC layer, while the energy in regime II was inversely proportional to the elastic modulus of PMC in the C(0/90)/A1203/C(0/90) and A(0/90)/A1203/A(0/90) laminated composites as shown in Table 1 and Table 3. The reason is that the energy in regime II is the elastic deformation energy of the PMC layer, which is defined as o2/2E, since the critical tensile stress is constant in the C(0/90)/A1203/ C(0/90) and A(0/90)/AI203/A(0/90) laminated composites. The energy in regime III was proportional to the fracture toughness of the outer PMC layer, because the energy absorption is entirely related to the fracture
Table 3 The energies absorbed in each regime during three-point bending of a monolithic AlzO3 and PMC/AleO3/PMClaminated composites Energies (kJ m -2)
El AI203
C(0/90)/A1203/C(0/90)
C( +45/- 45)/A1203/C(+45/-45)
A(O/90)/A1203/A(O/90) A( + 4 5 / - 45)/AI203/A(+45/-45)
Eli
EIII
13.5 7.4 25.2 5.5
0.2 21.0 1.2 > 30.0
0.5
1.4 1.0 1.1 0.9
of the outer PMC layer. As a result, the PMC with high elastic modulus is effective in suppressing the crack initiation at the A1203 layer in regime I of the PMC/ AI203/PMC laminated composite, while the PMC with high flexural strength with high fracture toughness is effective in enhancing the fracture resistance of the PMC/A1203/PMC laminated composite.
4. Conclusions
The crack propagation behaviour during three-point bending of a monolithic A1203 and PMC/AI203/PMC composites laminated with four diffrent PMCs has been investigated. The fracture behaviour of the PMC/ A1203/PMC laminated composites was sensitively affected by the properties of the PMCs. The total fracture energy of the PMC/AI203/PMC laminated composite increased by more than two orders of magnitude compared with that of monolithic AI203. The three-point bending process of the PMC/AI203/PMC laminated composite was divided into three regions (I, II, III) related to the crack initiation and propagation. In regime I, the PMC/AI203/PMC composite deformed elastically. In regime II, the PMC layers deformed elastically and the crack was initiated and opened in the AI2 03 layer. The crack initiation stress in the A1203 layer is proportional to the elastic modulus of the PMC. In regime III, the PMC/A1203/PMC lami-
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nated composites were fractured by debonding at the A1203-PMC interface in C ( 0 / 9 0 ) / A 1 2 0 3 / C ( 0 / 9 0 ) and A(0/90)/AI203/A(0/90 ) laminated composites, while the outer PMC layers were deformed without complete debonding at the AI203-PMC interface in C( + 4 5 / - 4 5 ) / A1203/C ( + 4 5 / - 4 5 ) and A( + 4 5 / - 45)/A1203/ A(+45/-45) laminated composites. The fracture modes of P M C / A I 2 0 3 / P M C laminated composites were determined by the ratio of flexural strength of PMC to interfacial strength at the A1203-PMC interface.
[3] R.A.J. Sambell, D.H. Bowen and D,C. Phillips, J. Mater. Sci., 7(1972) 663. [4] K.M. Prewo and J.J. Brennan, J. Mater. Sci., 17 (1982) 1201. [5] D.H. Bowen, D.C. Phillips, R.A.J. Sambell and A. Briggs, in Proc. Int. Conf. on the Mechanical Properties of Materials,
[6] [7] [8] [9] [10]
References [1] RE Becher and G.C. Wei, J. Am. Ceram. Soc., 67 (1984) 298. [2] R.W. Rice, Ceram. Eng. Sci. Proc., 2 (1981) 661.
163
[11] [12] [13]
Society of Metals, Japan, 1972, p. 123. K.T.Faber and A.G. Evans, A cta Metall., 31 ( 1983 ) 565. M.D. Thouless and A.G. Evans, Acta Metall., 36 (1988) 517. A.G. Evans and R.M. Mcmeeking, Acta Metall., 34 (1986) 2435. A.G. Evans and K.T. Faber, J. Am. Ceram. Soc., 67(1984) 255. W.J. Clegg, K. Kendall, N. McN. Alford, T.W. Button and J.D. Birchall, Nature (London), 347 (1990) 455. A.J. Phillips, W.J. Clegg and T.W. Clyne, Composites, 24 (1993) 166. Y, Leng and T.H. Courtney, J. Mater. Sci., 24 (1989) 2006. Y. Leng and T.H. Courtney, Metall. Trans. A, 21 (1990) 2159.