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Impact Performance of GFRP Laminates with Modified Epoxy Resin
Available online at www.sciencedirect.com
ScienceDirect Procedia Engineering 167 (2016) 160 – 167
Comitato Organizzatore del Convegno Internazionale DRaF 2016, c/o Dipartimento di Ing. Chimica, dei Materiali e della Prod.ne Ind.le
Impact performance of GFRP laminates with modified epoxy resin I. Papaa*, M.R.Ricciardib, V. Antonuccib, V.Loprestoa , A. Langellaa a
Department of Chemical, Materials Engineering and Industrial Production, University of Naples Federico II, Piazzale Vincenzo Tecchio 80, 80125 Naples b Italy IPCB Institute for Polymers, Composites and materials_CNR National Research Council P.le E. Fermi, 1 (Portici) Naples, Italy
Abstract Glass fiber composite materials in epoxy resin with different content of a nitrile rubber modified hybrid resin were manufactured by infusion with two different rubber concentrations. SX 10 epoxy resin was modified to improve the response of the laminates under impact loads. At the aim to test the improvement of the impact resistance over the conventional epoxy resin system, the rectangular specimens 100*150 mm2 were dynamically loaded in the center by a falling weight machine, Ceast Fractovis, using a cylindrical impactor with a hemispherical nose 19,8 mm in diameter and a total mass of 3.6 kg. Impact tests were carried out at penetration to obtain the complete load-displacement curve useful to measure the penetration energy and to highlight the characteristics points for the increasing energies evaluation , 5J, 10J and 20J, to investigate the damage start and propagation. After the impact tests, the specimens were observed by visual inspection to investigate the delamination extension whereas a confocal microscope was used for the indentation measurements. The obtained results on the modified epoxy system were compared to neat GFRP laminates impact performances. No significant impact performance difference was recorded between samples with different nitrile rubber modifier content. A higher indentation was recorded on the modified samples related with a lower delamination extension. It could represent a good practical results since from a simple external damage measurement it can be possible to obtain information about a low internal delamination. 2016The TheAuthors. Authors. Published by Elsevier Ltd.is an open access article under the CC BY-NC-ND license © 2016 © Published by Elsevier Ltd. This (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility ofthe Organizing Committee of DRaF2016. Peer-review under responsibility of the Organizing Committee of DRaF2016 Keywords: GFRP, impact, delamination, elastomer.
1. Introduction Composites laminates made by glass fibers reinforcements in an epoxy resin, is a very common composite material characterized by good physical, chemical, thermal, and mechanical properties. Epoxy resin is the most commonly used, in particular for aerospace applications, since its good resistance to higher temperatures, good corrosion resistance, mechanical and electrical properties, no styrene emission and more compact failure modes respect to vinylester. However, since the anisotropic nature of composites and the subsequent particular mechanism of damage formation,
1877-7058 © 2016 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license
(http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the Organizing Committee of DRaF2016
doi:10.1016/j.proeng.2016.11.683
I. Papa et al. / Procedia Engineering 167 (2016) 160 – 167
the impact performance of structural components made of fibre-reinforced plastic is often one of the limiting properties during the design . Even a low-energy impact can lead to a severe weakening of the load capacity as a result of delamination caused by the concentrated out of-plane loads. In particular, a low-velocity impact loading causes damages inside the laminate, which are difficult to detect by visual inspections. In addition to the efforts to improve the damage initiation and propagation as a result of impact loads, the improvement of the impact damage resistance of fibre-reinforced plastic componentes has been the subject of the investigations of many researchers for a long time. Nash et al. [1] give an extensive overview of different methods to improve the impact and post-impact performance of carbon fibre-reinforced composites (CFRP). Good results could be achieved by increasing the toughness of the matrix. This can be accomplished, for example, by the addition of liquid rubber [2,3] or thermoplastic particles [4,5]. In this paper, low velocity impact tests at penetration and at three different impact energy values (5J, 10J and 20J), were performed on glass fiber composite laminates made by vacuum infusion process. Epoxy resin with different content of a nitrile rubber modifier were considered to impregnate the fibers. The delamination was investigated by visual inspection and the results obtained on the laminates with different continent of nitrile rubber modifier were compared to the neat ones. In terms of damaged area, a general better behavior of modified resin was noted.
2. Materials and experimental set-up The composite laminates were manufactured by vacuum infusion process. The employed technology consists of fibre reinforcement impregnated by means of a thermosetting liquid resin driven by vacuum (VIP; vacuum infusion process). Dry unidirectional layers of E-glass fibre were overlapped following the stacking sequence [(0), (90)] 4. The liquid resin is a blend of a commercial bicomponent epoxy resin ISX_10 by Mates Italiana and a nitrile rubber modified epoxy resin, Polydis 3650 by Struktol . The resin system was modified by dispersing at 20% w/w and 30%w/w the rubber. After the infiltration of epoxy resin, the laminates have been cured at 90°C for 50 min. The final laminates have nominal thickness equal to 2.3 mm. The fibre volume fraction was Vf = 48%. Impact tests were carried out by a falling weight machine, Ceast Fractovis, at complete penetration to obtain and study the whole load curve, and at different increasing energy levels, 5J, 10J and 20J, to carry out the so called indentation tests useful to study the damage start and evolution. From the whole curves it was possible to know the penetration energy as well as the different energy values, in correspondence of characteristic points related to the internal damage, for the indentation tests. The rectangular specimens, 100x150 mm, cut by a diamond saw from the original panels, were supported by the clamping device suggested by the EN6038 Standard and were centrally loaded by an instrumented cylindrical impactor with a hemispherical nose 19,8 mm in diameter. The total minimum mass of 3.6 kg was considered that combined with the drop heights allowed to obtain the selected impact energies. After the impact tests, the specimens were investigated by visual inspection to observe the internal damage whereas a confocal microscope, Leica DCM3D, was used for the indentation depth measurements. 3. Results When Figure 1 compares the contact force-deflection curves for GFRP laminates during each experimental low velocity impact tests up to penetration. The neat composite is indicated with the suffix N, the hybrid composites with 20% w/w and 30% of rubber are indicated with the suffix R and R30 respectively. Clearly, the structural rigidity, represented by the initial slope of curves, Increases with the nitrile rubber above 20 wt%. No delamination effect, or fibers failure seem to occur since no load drops or changing in slope are evidenced. Interestingly, the maximum force decreases as the epoxy modifier percentage increases. Impact penetration parameters as load peak (Fmax), Energy at load peak (Energy), time at load peak, deflection at load peak and the penetration energy (Up), measured on the load curve penetration, are reported in Table 1.
161
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I. Papa et al. / Procedia Engineering 167 (2016) 160 – 167 Table 1. Low velocity impact penetration data Type
Properties at maximum load Energy (J) time (ms) 46 2.70 40 2.9 51 3.44
Fmax(N) 12521 11554 11002
N R R30
Deflection (mm) 8.85 8.38 9.02
Up (J) 85 97 89
14000 N_PEN R_PEN R30_PEN
12000
F [N]
10000
8000
6000
4000
2000
0 0
5
10
15
20
25
30
d [mm] Fig. 1: Force-deflection penetration curves for composites with various epoxy modifier contenent N:neat; R: 20%wt; R30: 30%wt
In Fig. 2, fig.3 and Fig. 4 typical load-deflection curves for the different samples impacted at different energy levels of 5, 10 and 20 J, are reported for the all specimens tested. The picture clearly shows that at different condition a closed type curve is obtained : the samples are not penetrated/perforated by the impactor which rebounds and the area enclosed in the loop is just the energy absorbed to create damage. No significant differences ,are noticeable for the neat and hybrid laminates On the other hand, a slight lowering of the curve for the laminate with 30 wt% of modifier, can be noticed at high deflection values (Figure 4).
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8000 N_5J R_5J R30_5J
F [N]
6000
4000
2000
0 0
2
4
6
8
d [mm] Fig 2. Force - deflection curves of composites with various epoxy modifier content (5J) N:neat; R: 20%wt; R30: 30%wt
8000 N_10J R_10J R30_10J
F [N]
6000
4000
2000
0 0
2
4
6
8
d [mm] Fig 3. Force - deflection curves of composites with various epoxy modifier content (10J) N:neat; R: 20%wt; R30: 30%wt
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8000 N_20J R_20J R30_20J
F [N]
6000
4000
2000
0 0
2
4
6
8
d [mm] Fig 4. Force - deflection curves of composites with various epoxy modifier content (20J) N:neat; R: 20%wt; R30: 30%wt
As expected, the maximum impact load, F, for each sample type increases as the impact energy, U, increases. Also the absorbed energy, Ua, increases at the increasing of the impact energy, Up, meaning that the effect of the increasing energies is like the increasing in rigidity and the internal damage increases. 8000 N R R30
Fmax [N]
6000
4000
2000
0 5
10
20
U [J] Fig. 5: Maximum impact load-impact energies for composites with various epoxy modifier contenent N:neat; R: 20%wt; R30: 30%wt
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I. Papa et al. / Procedia Engineering 167 (2016) 160 – 167
4.0 N R R30
3.5
Ua [J/mm]
3.0 2.5 2.0 1.5 1.0 0.5 0.0 4
6
8
10
12
14
16
18
20
22
U [J] Fig. 6: Absorbed energy, Ua, versus impact energy, U. N:neat; R: 20%wt; R30: 30%wt
The damaged area, A, were correlated (Fig. 7 and Fig. 8) to the impact energy, U, and the maximum impact load, Fmax: a linear relationship was obtained in the range of the adopted impact energies. As you can observe, the delaminated area is lower for the panels with a rubber percentage equal to 30% by weight of the resin respect to the neat one. No significant difference are observed between the panels with different concentration of rubber. This behavior could be justified by increased absorbed energy in the case of the modified panels. However, this result is not reflected by the trend ratio of the absorbed energy, Ua, versus the impact energy, U (Fig.6). Only for the impact energy equal to 20 J a different damage behaviour is recorded . 500
500 N R R30
N R R30
400
300
A [mm2]
A [mm2]
400
200
300
200
100
100
0
0 0
5
10
15
20
25
U [J]
Fig.7. Delaminated area, A, against impact energy, U
0
2000
4000
F
6000
8000
[N]
max
Fig. 8. Delaminated area, A, against maximum force, Fmax
In Fig. 9, the ratio between indentation depth, I, the plastic deformation left by the indenter on the surface of the impacted laminate and the penetrator tip diameter, D t, was plotted against the ratio between the impact energy and the penetration one, U/Up . An increasing of I/Dt with the increasing of U/Up was noted. The increasing trend is lower, the higher is the U/Up ratio stretching to an horizontal asymptote The effect of the minimum change of the panels thickness on the indantation was eliminated considering the ratio between the impact energy, U, and the perforation one, Up [6]. Even if, the modified samples delaminated area results minor than the neat one, the depth I results bigger for the first panel type. Plotting, then, the indentation, I, against the delaminated area, A, (Fig. 10), it
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I. Papa et al. / Procedia Engineering 167 (2016) 160 – 167
is simple to note that the trend slope increases for the modified samples (R, R30) : comparing the two types of panels (Neat and modified) for a higher delaminated Area of the one, a minor indentation depth of the other is registered.
14 N R R30
12
10
I/Dt
8
6
4
2
0 0.00
0.05
0.10
0.15
0.20
0.25
U/Up Fig. 9. Indentation depth, I/Dt, against impact Energy, U/Up
260 240 220
I [μm]
200 180 160 140 120
N R R30
100 80 0
100
200
300 2
400
A [mm ] Fig. 10. Indentation depth, I, against delaminated area, A
500
I. Papa et al. / Procedia Engineering 167 (2016) 160 – 167
Conclusions Glass fiber composite laminates in epoxy resin with different content of a nitrile rubber modifier were manufactured and tested by a falling dart machine operating at impact energies equal to 5J, 10 J and 20 J. Measurements revealed that: x No important impact performances difference was recorded between samples with different nitrile rubber modifier content; x During the penetration tests, a slight lowering of the curve for the laminate with 30 wt% of modifier can be noticed, especially at U=20 J; x A linear relationship between the delaminated area, A, versus the maximum load and the impacted energy, U, was obtained. The modified samples delaminated area results lower than the neat one even if the absorbed energy results the same in each case; x The depth of the indentation, I, obtained in the impact tests was measured. A higher indentation value is recorded for the modified samples. Plotting, then, the indentation, I, against the delaminated area, A, it is simple to note that comparing the two types of panels (Neat and modified) for a lower delaminated area of the one, correspond to a higher indentation depth.
Acknowledgement The authors gratefully acknowledge the ONR Solid Mechanics Program, in the person of Dr. Yapa D.S. Rajapakse, Program Manager, for the financial support provided to this research. References [1] Nash NH, Young TM, McGrail PT, Stanley WF. Inclusion of a thermoplastic phase to improve impact and post-impact performance of carbon fibre reinforced thermosetting composites – a review. Mater Des 2015;85:582–97. [2] Hengshi Z, Shiai X. A new method to prepare rubber toughened epoxy with high modulus and high impact strength. Mater Lett 2014;121:238–40. [3] Nguyen FN, Natsume N, Arai N, Yoshioka K. High performances of core-shell (dendrimer) nanoparticles in carbon fibre/epoxy composites. In: 18th International conference on composite materials (ICCM 18), Korea; 2011. [4] Bull DJ, Spearing SM, Sinclair I, Helfen L. Three-dimensional assessment of low velocity impact damage in particle toughened composite laminates using micro-focus X-ray computed tomography and synchrotron radiation aluminography. Compos A 2013;52:62–9. [5] Bull DJ, Scott AE, Spearing SM, Sinclair I. The influence of toughening-particles in CFRPs on low velocity impact damage resistance performance. Compos A 2014;58:47–55. [6] G. Caprino and V. Lopresto, ‘The significance of indentation in the inspection of carbon fibre reinforced plastic panels damaged by lowvelocity impact’, Compos. Sci. Technol. 60/7, 1003-1012 (2000)
167
ScienceDirect Procedia Engineering 167 (2016) 160 – 167
Comitato Organizzatore del Convegno Internazionale DRaF 2016, c/o Dipartimento di Ing. Chimica, dei Materiali e della Prod.ne Ind.le
Impact performance of GFRP laminates with modified epoxy resin I. Papaa*, M.R.Ricciardib, V. Antonuccib, V.Loprestoa , A. Langellaa a
Department of Chemical, Materials Engineering and Industrial Production, University of Naples Federico II, Piazzale Vincenzo Tecchio 80, 80125 Naples b Italy IPCB Institute for Polymers, Composites and materials_CNR National Research Council P.le E. Fermi, 1 (Portici) Naples, Italy
Abstract Glass fiber composite materials in epoxy resin with different content of a nitrile rubber modified hybrid resin were manufactured by infusion with two different rubber concentrations. SX 10 epoxy resin was modified to improve the response of the laminates under impact loads. At the aim to test the improvement of the impact resistance over the conventional epoxy resin system, the rectangular specimens 100*150 mm2 were dynamically loaded in the center by a falling weight machine, Ceast Fractovis, using a cylindrical impactor with a hemispherical nose 19,8 mm in diameter and a total mass of 3.6 kg. Impact tests were carried out at penetration to obtain the complete load-displacement curve useful to measure the penetration energy and to highlight the characteristics points for the increasing energies evaluation , 5J, 10J and 20J, to investigate the damage start and propagation. After the impact tests, the specimens were observed by visual inspection to investigate the delamination extension whereas a confocal microscope was used for the indentation measurements. The obtained results on the modified epoxy system were compared to neat GFRP laminates impact performances. No significant impact performance difference was recorded between samples with different nitrile rubber modifier content. A higher indentation was recorded on the modified samples related with a lower delamination extension. It could represent a good practical results since from a simple external damage measurement it can be possible to obtain information about a low internal delamination. 2016The TheAuthors. Authors. Published by Elsevier Ltd.is an open access article under the CC BY-NC-ND license © 2016 © Published by Elsevier Ltd. This (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility ofthe Organizing Committee of DRaF2016. Peer-review under responsibility of the Organizing Committee of DRaF2016 Keywords: GFRP, impact, delamination, elastomer.
1. Introduction Composites laminates made by glass fibers reinforcements in an epoxy resin, is a very common composite material characterized by good physical, chemical, thermal, and mechanical properties. Epoxy resin is the most commonly used, in particular for aerospace applications, since its good resistance to higher temperatures, good corrosion resistance, mechanical and electrical properties, no styrene emission and more compact failure modes respect to vinylester. However, since the anisotropic nature of composites and the subsequent particular mechanism of damage formation,
1877-7058 © 2016 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license
(http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the Organizing Committee of DRaF2016
doi:10.1016/j.proeng.2016.11.683
I. Papa et al. / Procedia Engineering 167 (2016) 160 – 167
the impact performance of structural components made of fibre-reinforced plastic is often one of the limiting properties during the design . Even a low-energy impact can lead to a severe weakening of the load capacity as a result of delamination caused by the concentrated out of-plane loads. In particular, a low-velocity impact loading causes damages inside the laminate, which are difficult to detect by visual inspections. In addition to the efforts to improve the damage initiation and propagation as a result of impact loads, the improvement of the impact damage resistance of fibre-reinforced plastic componentes has been the subject of the investigations of many researchers for a long time. Nash et al. [1] give an extensive overview of different methods to improve the impact and post-impact performance of carbon fibre-reinforced composites (CFRP). Good results could be achieved by increasing the toughness of the matrix. This can be accomplished, for example, by the addition of liquid rubber [2,3] or thermoplastic particles [4,5]. In this paper, low velocity impact tests at penetration and at three different impact energy values (5J, 10J and 20J), were performed on glass fiber composite laminates made by vacuum infusion process. Epoxy resin with different content of a nitrile rubber modifier were considered to impregnate the fibers. The delamination was investigated by visual inspection and the results obtained on the laminates with different continent of nitrile rubber modifier were compared to the neat ones. In terms of damaged area, a general better behavior of modified resin was noted.
2. Materials and experimental set-up The composite laminates were manufactured by vacuum infusion process. The employed technology consists of fibre reinforcement impregnated by means of a thermosetting liquid resin driven by vacuum (VIP; vacuum infusion process). Dry unidirectional layers of E-glass fibre were overlapped following the stacking sequence [(0), (90)] 4. The liquid resin is a blend of a commercial bicomponent epoxy resin ISX_10 by Mates Italiana and a nitrile rubber modified epoxy resin, Polydis 3650 by Struktol . The resin system was modified by dispersing at 20% w/w and 30%w/w the rubber. After the infiltration of epoxy resin, the laminates have been cured at 90°C for 50 min. The final laminates have nominal thickness equal to 2.3 mm. The fibre volume fraction was Vf = 48%. Impact tests were carried out by a falling weight machine, Ceast Fractovis, at complete penetration to obtain and study the whole load curve, and at different increasing energy levels, 5J, 10J and 20J, to carry out the so called indentation tests useful to study the damage start and evolution. From the whole curves it was possible to know the penetration energy as well as the different energy values, in correspondence of characteristic points related to the internal damage, for the indentation tests. The rectangular specimens, 100x150 mm, cut by a diamond saw from the original panels, were supported by the clamping device suggested by the EN6038 Standard and were centrally loaded by an instrumented cylindrical impactor with a hemispherical nose 19,8 mm in diameter. The total minimum mass of 3.6 kg was considered that combined with the drop heights allowed to obtain the selected impact energies. After the impact tests, the specimens were investigated by visual inspection to observe the internal damage whereas a confocal microscope, Leica DCM3D, was used for the indentation depth measurements. 3. Results When Figure 1 compares the contact force-deflection curves for GFRP laminates during each experimental low velocity impact tests up to penetration. The neat composite is indicated with the suffix N, the hybrid composites with 20% w/w and 30% of rubber are indicated with the suffix R and R30 respectively. Clearly, the structural rigidity, represented by the initial slope of curves, Increases with the nitrile rubber above 20 wt%. No delamination effect, or fibers failure seem to occur since no load drops or changing in slope are evidenced. Interestingly, the maximum force decreases as the epoxy modifier percentage increases. Impact penetration parameters as load peak (Fmax), Energy at load peak (Energy), time at load peak, deflection at load peak and the penetration energy (Up), measured on the load curve penetration, are reported in Table 1.
161
162
I. Papa et al. / Procedia Engineering 167 (2016) 160 – 167 Table 1. Low velocity impact penetration data Type
Properties at maximum load Energy (J) time (ms) 46 2.70 40 2.9 51 3.44
Fmax(N) 12521 11554 11002
N R R30
Deflection (mm) 8.85 8.38 9.02
Up (J) 85 97 89
14000 N_PEN R_PEN R30_PEN
12000
F [N]
10000
8000
6000
4000
2000
0 0
5
10
15
20
25
30
d [mm] Fig. 1: Force-deflection penetration curves for composites with various epoxy modifier contenent N:neat; R: 20%wt; R30: 30%wt
In Fig. 2, fig.3 and Fig. 4 typical load-deflection curves for the different samples impacted at different energy levels of 5, 10 and 20 J, are reported for the all specimens tested. The picture clearly shows that at different condition a closed type curve is obtained : the samples are not penetrated/perforated by the impactor which rebounds and the area enclosed in the loop is just the energy absorbed to create damage. No significant differences ,are noticeable for the neat and hybrid laminates On the other hand, a slight lowering of the curve for the laminate with 30 wt% of modifier, can be noticed at high deflection values (Figure 4).
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I. Papa et al. / Procedia Engineering 167 (2016) 160 – 167
8000 N_5J R_5J R30_5J
F [N]
6000
4000
2000
0 0
2
4
6
8
d [mm] Fig 2. Force - deflection curves of composites with various epoxy modifier content (5J) N:neat; R: 20%wt; R30: 30%wt
8000 N_10J R_10J R30_10J
F [N]
6000
4000
2000
0 0
2
4
6
8
d [mm] Fig 3. Force - deflection curves of composites with various epoxy modifier content (10J) N:neat; R: 20%wt; R30: 30%wt
164
I. Papa et al. / Procedia Engineering 167 (2016) 160 – 167
8000 N_20J R_20J R30_20J
F [N]
6000
4000
2000
0 0
2
4
6
8
d [mm] Fig 4. Force - deflection curves of composites with various epoxy modifier content (20J) N:neat; R: 20%wt; R30: 30%wt
As expected, the maximum impact load, F, for each sample type increases as the impact energy, U, increases. Also the absorbed energy, Ua, increases at the increasing of the impact energy, Up, meaning that the effect of the increasing energies is like the increasing in rigidity and the internal damage increases. 8000 N R R30
Fmax [N]
6000
4000
2000
0 5
10
20
U [J] Fig. 5: Maximum impact load-impact energies for composites with various epoxy modifier contenent N:neat; R: 20%wt; R30: 30%wt
165
I. Papa et al. / Procedia Engineering 167 (2016) 160 – 167
4.0 N R R30
3.5
Ua [J/mm]
3.0 2.5 2.0 1.5 1.0 0.5 0.0 4
6
8
10
12
14
16
18
20
22
U [J] Fig. 6: Absorbed energy, Ua, versus impact energy, U. N:neat; R: 20%wt; R30: 30%wt
The damaged area, A, were correlated (Fig. 7 and Fig. 8) to the impact energy, U, and the maximum impact load, Fmax: a linear relationship was obtained in the range of the adopted impact energies. As you can observe, the delaminated area is lower for the panels with a rubber percentage equal to 30% by weight of the resin respect to the neat one. No significant difference are observed between the panels with different concentration of rubber. This behavior could be justified by increased absorbed energy in the case of the modified panels. However, this result is not reflected by the trend ratio of the absorbed energy, Ua, versus the impact energy, U (Fig.6). Only for the impact energy equal to 20 J a different damage behaviour is recorded . 500
500 N R R30
N R R30
400
300
A [mm2]
A [mm2]
400
200
300
200
100
100
0
0 0
5
10
15
20
25
U [J]
Fig.7. Delaminated area, A, against impact energy, U
0
2000
4000
F
6000
8000
[N]
max
Fig. 8. Delaminated area, A, against maximum force, Fmax
In Fig. 9, the ratio between indentation depth, I, the plastic deformation left by the indenter on the surface of the impacted laminate and the penetrator tip diameter, D t, was plotted against the ratio between the impact energy and the penetration one, U/Up . An increasing of I/Dt with the increasing of U/Up was noted. The increasing trend is lower, the higher is the U/Up ratio stretching to an horizontal asymptote The effect of the minimum change of the panels thickness on the indantation was eliminated considering the ratio between the impact energy, U, and the perforation one, Up [6]. Even if, the modified samples delaminated area results minor than the neat one, the depth I results bigger for the first panel type. Plotting, then, the indentation, I, against the delaminated area, A, (Fig. 10), it
166
I. Papa et al. / Procedia Engineering 167 (2016) 160 – 167
is simple to note that the trend slope increases for the modified samples (R, R30) : comparing the two types of panels (Neat and modified) for a higher delaminated Area of the one, a minor indentation depth of the other is registered.
14 N R R30
12
10
I/Dt
8
6
4
2
0 0.00
0.05
0.10
0.15
0.20
0.25
U/Up Fig. 9. Indentation depth, I/Dt, against impact Energy, U/Up
260 240 220
I [μm]
200 180 160 140 120
N R R30
100 80 0
100
200
300 2
400
A [mm ] Fig. 10. Indentation depth, I, against delaminated area, A
500
I. Papa et al. / Procedia Engineering 167 (2016) 160 – 167
Conclusions Glass fiber composite laminates in epoxy resin with different content of a nitrile rubber modifier were manufactured and tested by a falling dart machine operating at impact energies equal to 5J, 10 J and 20 J. Measurements revealed that: x No important impact performances difference was recorded between samples with different nitrile rubber modifier content; x During the penetration tests, a slight lowering of the curve for the laminate with 30 wt% of modifier can be noticed, especially at U=20 J; x A linear relationship between the delaminated area, A, versus the maximum load and the impacted energy, U, was obtained. The modified samples delaminated area results lower than the neat one even if the absorbed energy results the same in each case; x The depth of the indentation, I, obtained in the impact tests was measured. A higher indentation value is recorded for the modified samples. Plotting, then, the indentation, I, against the delaminated area, A, it is simple to note that comparing the two types of panels (Neat and modified) for a lower delaminated area of the one, correspond to a higher indentation depth.
Acknowledgement The authors gratefully acknowledge the ONR Solid Mechanics Program, in the person of Dr. Yapa D.S. Rajapakse, Program Manager, for the financial support provided to this research. References [1] Nash NH, Young TM, McGrail PT, Stanley WF. Inclusion of a thermoplastic phase to improve impact and post-impact performance of carbon fibre reinforced thermosetting composites – a review. Mater Des 2015;85:582–97. [2] Hengshi Z, Shiai X. A new method to prepare rubber toughened epoxy with high modulus and high impact strength. Mater Lett 2014;121:238–40. [3] Nguyen FN, Natsume N, Arai N, Yoshioka K. High performances of core-shell (dendrimer) nanoparticles in carbon fibre/epoxy composites. In: 18th International conference on composite materials (ICCM 18), Korea; 2011. [4] Bull DJ, Spearing SM, Sinclair I, Helfen L. Three-dimensional assessment of low velocity impact damage in particle toughened composite laminates using micro-focus X-ray computed tomography and synchrotron radiation aluminography. Compos A 2013;52:62–9. [5] Bull DJ, Scott AE, Spearing SM, Sinclair I. The influence of toughening-particles in CFRPs on low velocity impact damage resistance performance. Compos A 2014;58:47–55. [6] G. Caprino and V. Lopresto, ‘The significance of indentation in the inspection of carbon fibre reinforced plastic panels damaged by lowvelocity impact’, Compos. Sci. Technol. 60/7, 1003-1012 (2000)
167