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Fracture of fibrous metal matrix composites containing discontinuities
Thermomechanicsl f a t i g u e o f a quasi-isotropic metal m a t r i x composite. MraoJumdar, B.S, and Newaz, G.M, c. Conf. Composite Materials: Fatigue and Fracture, Lake Buena Vista, Florida, USA, 6 - 7 Nov. 1989 vol 3, 7 3 2 - 7 5 2 In-phase thermomechamcal fatigue (TMF) and elevated temperature isothermal fatigue {IF) expertments were conducted on a [0, ±45,90J s Ti 15-3/SCS6 composite under load control A correlation was obtained between the stabilized mechanical strain range and TMF hfe. TMF life was found to be s~gntficantly shorter than iF hfe when comparisons were made either on a stress-range or a gross mechanical strainrange basis. Damage modes were investigated using optical and scanning electron microscopy. The primary damage mode in IF specimens was transverse microcracklng oriented perpendicular to the loading axis. In TMF specimens, although s~mllar damage was observed very close to the fracture surface, the primary damage modes were inter-ply delaminat;on and fibre-matrix debonding. Ltm~ted experiments were performed where damage was monitored using a replication technique on the specimen edges. These experiments confirmed delamlnation and debondlng m TMF and thermally cycled specimens. Wavelength disperstve spectroscopic (WDS) analysis showed carbon-rich zones along many ply-to-ply interfaces, and these zones may have accelerated delamlnat~on cracking Finite element analysis indicated that the maximum delammatlon stress occurred at the minimum temperature in the TMF expercments The fatigue data of Ti-15-3/SCS6 composite, from this and other investigations, were plotted rn the form of 0° fibre stress range vs. logarithm of fatigue life. This phenomenologlcal plot indicated a similar trend for various data sets, but the exact mechanisms remain to be determined
Fatigue crack growth in a unidirectional SCS-6/Ti-15-3 composite. Kantzos, P., Telesman, J. and Ghosn, L. Prec. Conf. Composite Materials: Fatigue and Fracture, Lake Buena Vista, Florida, USA, 6 - 7 Nov. 1989 vet 3, 7 1 1 - 7 3 1 An investigation was conducted to characterize and model the fatigue crack growth (FCG) behaviour of a SCS-8/Ti-15-3 metal matrix composite. Part of the study was conducted using a fatigue loading stage mounted inside a scanning electron microscope (SEM). The unidirecttonal composite was tested in the [0] 8(that ts, longitudinal) and [90] 8(that is, transverse) orientatmns. For comparison purposes, unreinforced matrix material produced by the identical process as the reinforced material was also tested The results of the study reveal that the fatigue crack growth behaviour of the composite ts a function of specimen geometry, fibre orientation, and the interaction of local stress fields with the highly antsotropic composite. In the case of [O] 8 onented single edge notch (SEN) specimens and [90] 8 oriented compact tension (CT) specimens, the crack growth was normal to the loading direction. However, for the [0] 8 CT specimens, the crack grew mestJy parallel to the loading and the fibre direct=on.
Fracture of fibrous m e t a l m a t r i x composites containing discontinuities. Bahei-EI-Din, Y.A. Proc. Conf Composite Materials: Fatigue and Fracture, Lake Buena Vista, Florida, USA, 6 - 7 Nov. 1989vol 3, 6 9 6 - 7 1 0 The work of Dvorak et al and Bahei-EI-Dm et al on fracture of umdlrect~onally reinforced B/AI specimens with a centre notch is extended here for specimens w~th other types of discontinuities. The experimental results obtained using 6061 AI panels reinforced with boron fibres indicate that long, discrete plastic shear zones simdar to those found at the notch tip are present in all specimens The plastic zones grow from the discontinuity in the fibre direction. The measured fracture strength was not affected by geometry of the notch; it ts only a functmn of the notch width/specimen width ratto. Finite element analysis of the specimens with centre square hole provided the plastic zone length and the local stresses. The results verified that the criterion controlhng fracture in centre-notched specimens is applicable to other notch geometries, Failure is controlled by a critical ratio of the largest principal stress tO off-axis unnotched strength in the principal direction, in a small representative volume In the vicinity of the notch.
Fatigue properties and fatigue fracture mechanisms of SiC whiskers or SiC particulate-reinforced eluminium composites. Masuda, C. and Tanaka, Y. J. Mater. ScL Jan, 1992 27, (2), 4 1 3 - 4 2 2 Fatigue properties and fracture mechanisms were examined for three commercially fabricated AI matrix composites containing SiC whiskers (SiCw) and SiC particles (SiCp) using a rotating bending test. The fatigue strengths were >60% higher for SaCw-A2024 composites than for the unremforced rolled material, while for the SiCp-A357 composites, fatigue strengths were also higher than for the unreinforced reference material. For the SiCp-A358 composttes at a volume fraction of 20%, the fatigue strength was slightly higher than that of the unreinforced material Fractography revealed that the Mode I fatigue crack was mitisted by the Stage I mechanism for the SiCw-A2024 and SICp-A357 composites, while for the SiCp-A358 composite, the fatigue crack initiated at the voids situated beneath the specimen surfaces. On the other hand, the fatigue crack propagated to the whisker-matrix interface following the formation of dimple patterns or the formation of striation patterns for SICw-A2024 composites, whde for the SiCp-A356 and SiCp/A357 composites the fatigue crack propagated in the matrix near the crack origin and strlanon patterns were found. Near final failure, dimple patterns, initiated at silicon carbtde particles, were frequently observed. Mode I fatigue crack initiation and propagation models were proposed for discontinuous fibre-reinforced AI composites it is suggested that the sihcon carbide whiskers or particles would have a very significant effect on the fatigue crack initmtton and crack propagation near the fatigue limit Graphs, photomicrographs 20 refs
Dynamic aspects of brass adhesion. Hewitt, N.L. Rubber World Dec. 1991 205, (3), 3 0 - 3 3 The disc failure procedure for dynamic evaluation of brass adhesion properties in brass-coated steel tyre cord provides an opportunity to measure rubber-to-metal bond fatigue life unencumbered by rubber cohesive failure. As a result of disc fatigue studies, two brass skim compounds can be recommended: one which combines silica with bonding resins, and one m which silica and sulphur are the only bonding ingredients Graphs 5 refs
64
Practical application of s h o t peening. Wi/hams, S The Shot Peener, Winter 1992 5, (4), 1 - 4 Shot peening is a cold working, surface conditioning process The mare objectwes are to improve resistance to fatigue, stress corrosion cracking, and surface wear. The effects of shot peening on fatigue life improvement in steels and vanous aJrcraft components are considered Graphs
The static and fatigue performance of welded joints for offshore platforms. Bramante, M, EUR Report 13636 1992 133 pp (in Italian) The use of newly developed thermal-mechamcal controlled process steels (TMCP) tn offshore platforms offers stgnlficant advantages, particularly with regard to weldabihty. However, both the fracture and fattgue performance of joints fabricated from these steels were not well estahhshed until recently, in fact, even for the steel traditionally used in offshore platforms (Euronorm Fe510D) its hkely service performance was not well documented, as the majority of testing on this steel had been camed out on reduced-scale laboratory tests of uncertain relevance to service behawour, whtle more reahstic testing such as full-scale testing tn seawater had been extremely bruited Thus this project was devised to provide detailed information on the performance of welded joints fabricated from three steels under condrtlons duphcating those offshore. Within this broad scope the project had two particular arms. (1) to provide a comparison between the performance of two TMCP steels and the tradittonal steel, (2) by significantly increasing the database on the performance of full-scale joints, to permit an assessment of the number of fundamental problems associated w~th joint life. To meet these aims, fatigue tests have been csrrted out on both plate-to-plate and tubular full-scale joints, while static toughness has been assessed by wide-plate tests, The steels considered were the traditional normahzed iN) Fe510D, a controlled roiled (CR) and a controlled roiled and accelerated cooled steel (AC). Full-scale fatigue tests on tubulars were carried out in bending on all steels and m tension on the N and CR steel. In 11 cases testing was in seawater with cathodic protection under reahstlc experimental conditions (frequency 0.35 Hz, temperature 10°C, cathodic voltage -850 mV, R = 0.1). Plateto-plate iT-butt) fatigue tests were carried out in four-point bending tn seawater under the same condlttons as above for the N and the AC steel and ~n air (R - 0.1, frequency 5 Hz, temperature ambient) for all steels. In all the fatpguetest programmes, procedures have been adopted (standardizing testing levels and repetition of tests) to ensure that statistically significant performance parameters were derived and that vahd comparisons were made between materials. Wide-plate tests were performed on manually welded joints from the N and the AC steel at low temperatures (-10 °C) Analys~s of the derived experimental data indtcates that the fatigue performance of each of the steels can be defined by log linear S-N curves and that the performance of the various steels is indrstinguishable in both plate-toplate and tubular tests. Both steels demonstrated a high reststance to crack propagatron in the wide-plate tests. As the fatigue performance of the new TCMP steels and the traditional steel is comparable, it is indicated that the new steel could be used wpth advantage m offshore platforms As a result of thvs programme, a large database, particularly with respect to the performance of full-scale welds In seawater with cathodic protectton, has been derwed It is demonstrated that the effectiveness of this type of protectton depends upon the applied load tevel, at high levels there is no benefit from its use while at low levels cathodic protection may, but does not necessarrly, enhance hfe Graphs. 25 refs.
Fatigue behaviour of welded joints in HSS steel for offshore structures. Bignonnet, A., Lieurade, H.P. and Vallet, C. EUR Report 13398 1992 96 pp (in French) The objective of this research is to study the fattgue behavlour of welded joints to evaluate the advantages in using a high-strength steel of type E460, in relation to the apphcation of post-weld improvement treatment. The experimental programme has been realized with two Wpes of assembhes; tubular X nodes, and T-joints s~mulatlng the hot spot area of tubular joints, in both cases testing has been performed under constant amplitude loading up to~107 cycles. The influence of a marine enwronment has been studied by tests in air and in seawater with cathodic protection. All the welded joints have been made with manual arc welding. An improved weld profile has been systematically done Two techniques have been applied to the post-weld ~mprovement' TIG dressing and shot peening (on tubular nodes and on T-joints). Lastly, fatigue tests under variable amplitude loading, using the common load sequence COLOS, have been performed in air on T-joints both improved weld profile as welded and shot peened. The conclustons can be summanzed as follows (1) Improved weld profile induces a shift of the weld toe into a lower stress concentration area in addition to a smoother toe geometry. This, combined wpth the use of high-strength steel, therefore leads to a better fatigue behaviour of the tubular connections. (2) A post-weld Improvement in the hot spot area allows a substantial rise m the admissible stresses in fatigue: approx 50% with TIC dressing and 100% wtth shot peening for constant amplitude loading. (3) Under random loading, fatigue tests on T-joints confirm the potential of shot peening. Whtle the tmprovement rn fatigue ~s not as pmportant as in constant amplitude loading, an increase In admissible nominal stress of >50% is observed in the range 106-107 cycles (4) in seawater, cathodtc protection allows the restoration of fatigue byes observed m air for long-term fattgue, beyond 106 cycles, on T-joints and on tubular nodes for the different post-weldrng conditions Graphs 17 refs.
pplicstion of the fracture mechanics approach to the fatigue behsviour welded tubular steel structures, van Straalen, Ij.J. Prec. 4th Int. Syrup. on Tubular Structures, Delft, The Netherlands, 26-28 June 1991 2 5 9 - 2 6 8 A brief description of the fracture mechanics (FM) approach for fatigue hfe and crack growth of welded tubular steel structures is given. Several assumptions made in the model are validated. To show the ability of this approach as a design tool, the effects of several parameters are determined by calculations and these are compared with experimental results. Some general remarks and recommendations are included
and fatigue behaviour of internally ring stiffened tubular Y joints. Gandhi, P., Rao, A.G.M., Murthy, D. S. and Raghava, G. Prec. 4th Int. Syrup. on Tubular Structures, Delft, The Netherlands, 26-28 June 1991 2 2 9 - 2 3 8 Static
The fatigue performance of steel tubular joints of offshore structures is of primary Jmportance in deciding the integrity of these structures. The fatigue analysis of
Int J Fatigue January 1993
Fatigue crack growth in a unidirectional SCS-6/Ti-15-3 composite. Kantzos, P., Telesman, J. and Ghosn, L. Prec. Conf. Composite Materials: Fatigue and Fracture, Lake Buena Vista, Florida, USA, 6 - 7 Nov. 1989 vet 3, 7 1 1 - 7 3 1 An investigation was conducted to characterize and model the fatigue crack growth (FCG) behaviour of a SCS-8/Ti-15-3 metal matrix composite. Part of the study was conducted using a fatigue loading stage mounted inside a scanning electron microscope (SEM). The unidirecttonal composite was tested in the [0] 8(that ts, longitudinal) and [90] 8(that is, transverse) orientatmns. For comparison purposes, unreinforced matrix material produced by the identical process as the reinforced material was also tested The results of the study reveal that the fatigue crack growth behaviour of the composite ts a function of specimen geometry, fibre orientation, and the interaction of local stress fields with the highly antsotropic composite. In the case of [O] 8 onented single edge notch (SEN) specimens and [90] 8 oriented compact tension (CT) specimens, the crack growth was normal to the loading direction. However, for the [0] 8 CT specimens, the crack grew mestJy parallel to the loading and the fibre direct=on.
Fracture of fibrous m e t a l m a t r i x composites containing discontinuities. Bahei-EI-Din, Y.A. Proc. Conf Composite Materials: Fatigue and Fracture, Lake Buena Vista, Florida, USA, 6 - 7 Nov. 1989vol 3, 6 9 6 - 7 1 0 The work of Dvorak et al and Bahei-EI-Dm et al on fracture of umdlrect~onally reinforced B/AI specimens with a centre notch is extended here for specimens w~th other types of discontinuities. The experimental results obtained using 6061 AI panels reinforced with boron fibres indicate that long, discrete plastic shear zones simdar to those found at the notch tip are present in all specimens The plastic zones grow from the discontinuity in the fibre direction. The measured fracture strength was not affected by geometry of the notch; it ts only a functmn of the notch width/specimen width ratto. Finite element analysis of the specimens with centre square hole provided the plastic zone length and the local stresses. The results verified that the criterion controlhng fracture in centre-notched specimens is applicable to other notch geometries, Failure is controlled by a critical ratio of the largest principal stress tO off-axis unnotched strength in the principal direction, in a small representative volume In the vicinity of the notch.
Fatigue properties and fatigue fracture mechanisms of SiC whiskers or SiC particulate-reinforced eluminium composites. Masuda, C. and Tanaka, Y. J. Mater. ScL Jan, 1992 27, (2), 4 1 3 - 4 2 2 Fatigue properties and fracture mechanisms were examined for three commercially fabricated AI matrix composites containing SiC whiskers (SiCw) and SiC particles (SiCp) using a rotating bending test. The fatigue strengths were >60% higher for SaCw-A2024 composites than for the unremforced rolled material, while for the SiCp-A357 composites, fatigue strengths were also higher than for the unreinforced reference material. For the SiCp-A358 composttes at a volume fraction of 20%, the fatigue strength was slightly higher than that of the unreinforced material Fractography revealed that the Mode I fatigue crack was mitisted by the Stage I mechanism for the SiCw-A2024 and SICp-A357 composites, while for the SiCp-A358 composite, the fatigue crack initiated at the voids situated beneath the specimen surfaces. On the other hand, the fatigue crack propagated to the whisker-matrix interface following the formation of dimple patterns or the formation of striation patterns for SICw-A2024 composites, whde for the SiCp-A356 and SiCp/A357 composites the fatigue crack propagated in the matrix near the crack origin and strlanon patterns were found. Near final failure, dimple patterns, initiated at silicon carbtde particles, were frequently observed. Mode I fatigue crack initiation and propagation models were proposed for discontinuous fibre-reinforced AI composites it is suggested that the sihcon carbide whiskers or particles would have a very significant effect on the fatigue crack initmtton and crack propagation near the fatigue limit Graphs, photomicrographs 20 refs
Dynamic aspects of brass adhesion. Hewitt, N.L. Rubber World Dec. 1991 205, (3), 3 0 - 3 3 The disc failure procedure for dynamic evaluation of brass adhesion properties in brass-coated steel tyre cord provides an opportunity to measure rubber-to-metal bond fatigue life unencumbered by rubber cohesive failure. As a result of disc fatigue studies, two brass skim compounds can be recommended: one which combines silica with bonding resins, and one m which silica and sulphur are the only bonding ingredients Graphs 5 refs
64
Practical application of s h o t peening. Wi/hams, S The Shot Peener, Winter 1992 5, (4), 1 - 4 Shot peening is a cold working, surface conditioning process The mare objectwes are to improve resistance to fatigue, stress corrosion cracking, and surface wear. The effects of shot peening on fatigue life improvement in steels and vanous aJrcraft components are considered Graphs
The static and fatigue performance of welded joints for offshore platforms. Bramante, M, EUR Report 13636 1992 133 pp (in Italian) The use of newly developed thermal-mechamcal controlled process steels (TMCP) tn offshore platforms offers stgnlficant advantages, particularly with regard to weldabihty. However, both the fracture and fattgue performance of joints fabricated from these steels were not well estahhshed until recently, in fact, even for the steel traditionally used in offshore platforms (Euronorm Fe510D) its hkely service performance was not well documented, as the majority of testing on this steel had been camed out on reduced-scale laboratory tests of uncertain relevance to service behawour, whtle more reahstic testing such as full-scale testing tn seawater had been extremely bruited Thus this project was devised to provide detailed information on the performance of welded joints fabricated from three steels under condrtlons duphcating those offshore. Within this broad scope the project had two particular arms. (1) to provide a comparison between the performance of two TMCP steels and the tradittonal steel, (2) by significantly increasing the database on the performance of full-scale joints, to permit an assessment of the number of fundamental problems associated w~th joint life. To meet these aims, fatigue tests have been csrrted out on both plate-to-plate and tubular full-scale joints, while static toughness has been assessed by wide-plate tests, The steels considered were the traditional normahzed iN) Fe510D, a controlled roiled (CR) and a controlled roiled and accelerated cooled steel (AC). Full-scale fatigue tests on tubulars were carried out in bending on all steels and m tension on the N and CR steel. In 11 cases testing was in seawater with cathodic protection under reahstlc experimental conditions (frequency 0.35 Hz, temperature 10°C, cathodic voltage -850 mV, R = 0.1). Plateto-plate iT-butt) fatigue tests were carried out in four-point bending tn seawater under the same condlttons as above for the N and the AC steel and ~n air (R - 0.1, frequency 5 Hz, temperature ambient) for all steels. In all the fatpguetest programmes, procedures have been adopted (standardizing testing levels and repetition of tests) to ensure that statistically significant performance parameters were derived and that vahd comparisons were made between materials. Wide-plate tests were performed on manually welded joints from the N and the AC steel at low temperatures (-10 °C) Analys~s of the derived experimental data indtcates that the fatigue performance of each of the steels can be defined by log linear S-N curves and that the performance of the various steels is indrstinguishable in both plate-toplate and tubular tests. Both steels demonstrated a high reststance to crack propagatron in the wide-plate tests. As the fatigue performance of the new TCMP steels and the traditional steel is comparable, it is indicated that the new steel could be used wpth advantage m offshore platforms As a result of thvs programme, a large database, particularly with respect to the performance of full-scale welds In seawater with cathodic protectton, has been derwed It is demonstrated that the effectiveness of this type of protectton depends upon the applied load tevel, at high levels there is no benefit from its use while at low levels cathodic protection may, but does not necessarrly, enhance hfe Graphs. 25 refs.
Fatigue behaviour of welded joints in HSS steel for offshore structures. Bignonnet, A., Lieurade, H.P. and Vallet, C. EUR Report 13398 1992 96 pp (in French) The objective of this research is to study the fattgue behavlour of welded joints to evaluate the advantages in using a high-strength steel of type E460, in relation to the apphcation of post-weld improvement treatment. The experimental programme has been realized with two Wpes of assembhes; tubular X nodes, and T-joints s~mulatlng the hot spot area of tubular joints, in both cases testing has been performed under constant amplitude loading up to~107 cycles. The influence of a marine enwronment has been studied by tests in air and in seawater with cathodic protection. All the welded joints have been made with manual arc welding. An improved weld profile has been systematically done Two techniques have been applied to the post-weld ~mprovement' TIG dressing and shot peening (on tubular nodes and on T-joints). Lastly, fatigue tests under variable amplitude loading, using the common load sequence COLOS, have been performed in air on T-joints both improved weld profile as welded and shot peened. The conclustons can be summanzed as follows (1) Improved weld profile induces a shift of the weld toe into a lower stress concentration area in addition to a smoother toe geometry. This, combined wpth the use of high-strength steel, therefore leads to a better fatigue behaviour of the tubular connections. (2) A post-weld Improvement in the hot spot area allows a substantial rise m the admissible stresses in fatigue: approx 50% with TIC dressing and 100% wtth shot peening for constant amplitude loading. (3) Under random loading, fatigue tests on T-joints confirm the potential of shot peening. Whtle the tmprovement rn fatigue ~s not as pmportant as in constant amplitude loading, an increase In admissible nominal stress of >50% is observed in the range 106-107 cycles (4) in seawater, cathodtc protection allows the restoration of fatigue byes observed m air for long-term fattgue, beyond 106 cycles, on T-joints and on tubular nodes for the different post-weldrng conditions Graphs 17 refs.
pplicstion of the fracture mechanics approach to the fatigue behsviour welded tubular steel structures, van Straalen, Ij.J. Prec. 4th Int. Syrup. on Tubular Structures, Delft, The Netherlands, 26-28 June 1991 2 5 9 - 2 6 8 A brief description of the fracture mechanics (FM) approach for fatigue hfe and crack growth of welded tubular steel structures is given. Several assumptions made in the model are validated. To show the ability of this approach as a design tool, the effects of several parameters are determined by calculations and these are compared with experimental results. Some general remarks and recommendations are included
and fatigue behaviour of internally ring stiffened tubular Y joints. Gandhi, P., Rao, A.G.M., Murthy, D. S. and Raghava, G. Prec. 4th Int. Syrup. on Tubular Structures, Delft, The Netherlands, 26-28 June 1991 2 2 9 - 2 3 8 Static
The fatigue performance of steel tubular joints of offshore structures is of primary Jmportance in deciding the integrity of these structures. The fatigue analysis of
Int J Fatigue January 1993