•Historical review of composites fatigue investigations.•Covers the last 75 years of fatigue investigations on composite materials.•Reviews the main approaches followed.•Describes the milestones in ...the field.
Investigations of the fatigue performance of composite materials have accompanied their introduction in several engineering domains since the 1950s. An abundance of publications have emerged dealing with the experimental investigation of the fatigue performance of composites under different loading and environmental conditions, as well as the development of theories for the modeling of the fatigue behavior and/or prediction of the fatigue life of the materials systems under consideration. This work aims to briefly review and present the history of fiber-reinforced polymer composite laminate fatigue investigations, dividing the last 70 years into three periods. The early 1950–1975 period, when the “new” materials and their behavior under (simple) fatigue loading patterns were discovered. The mature, 1975–2000 period, when more loading and material parameters were investigated and the basic theoretical background was established. And finally, the later period, in the new millennium, when more detailed experimental campaigns were performed (assisted by developments in a multitude of engineering and scientific fields) and parameters that had previously been overlooked by researchers were taken into account.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
•Investigates unexpected quasi static and fatigue failure of structural adhesives.•Use FE analyses to support the experimental evidence.•Shows high speed camera footage of the failure.•Reveals ...frequency effects on the tab failures.
This paper presents the results of an experimental campaign designed specifically to investigate unexpected and unwanted failures observed during the quasi-static and fatigue tensile loading of structural adhesives. Simple finite element models were also developed to support the arguments drawn from the experimental investigations. Particular parameters causing tab and asymmetrical failures in the bulk of dog-bone adhesive specimens were investigated. Artificial defects at the tab-adhesive interface, causing stress concentrations, intentionally misaligned tabs creating bending moments, different tab manufacturing, different fatigue loading frequency, and different grip pressure, were all considered in this analysis. In addition to the traditional instrumentation, a high-speed camera was also implemented to assist the observations. Experimental results showed that the tab failure occurrence is linked to the grip pressure, which shall be minimized. Other parameters such as grip alignment, tab taper, and loading frequency proved to also have a sizable effect on tab failure.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
•Fatigue behavior of (±45)2s glass/epoxy composite laminates was investigated.•Different stress levels led to different damage distributions.•Final fracture surfaces changed with stress ...levels.•Evolution of fatigue parameters was investigated.•Total dissipated energy was calculated for each stress level.
The fatigue behavior of (±45)2S angle-ply glass/epoxy composite laminates was investigated. Rectangular specimens were subjected to constant amplitude fatigue loading at different stress levels, with stress ratio 0.1 until failure. A video-extensometer and an infrared thermal camera were employed respectively to measure the evolution of strain and the self-generated temperature during the fatigue experiments. Using a digital camera and microscope, the progression of damage at the different locations and the fracture surfaces were also studied. At higher stress levels the damage was severe and localized and caused fiber pull-out failure at short lifetimes; however, by decreasing the fatigue stress level, a more uniform distribution of less severe damage was observed and fiber breakage prevailed, which led to a longer fatigue life. When the number of cycles was increased, the fatigue stiffness dropped at a higher rate at higher stress levels at the same age due to the localized and intense damage growth. The fatigue stiffness at failure, however, decreased more at lower stress levels than at higher ones, which was attributed to the material’s greater capacity to withstand damage. The dissipated energy increased with the number of cycles and fatigue stress level due to more friction in the area of the unbounded regions; the magnitude of the total energy dissipation (TDE) however significantly decreased as the fatigue stress level increased.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
•The 2D Mode I fracture behavior of composite laminates was investigated.•Cohesive elements were employed to model the fiber bridging.•The pre-crack shape mainly affected the initiation and early ...propagation stages.•The loading zone shape mainly affected the crack shape during stable propagation.•The fracture resistance affected both stiffness and fracture response.
The two-dimensional (2D) delamination growth in fiber-reinforced polymer (FRP) laminates with in-plane isotropy under Mode I loading condition was numerically investigated using finite element analyses. Two sizes of plate models were developed, focusing on different fracture stages. Cohesive elements were employed to simulate the fracture behavior in the presence of large-scale bridging (LSB). The influences of the pre-crack shape/area, loading zone shape/area and fracture resistance were parametrically studied. It was found that either a flatter pre-crack shape or a flatter loading zone shape could result in higher initial structural stiffness and less uniform distribution of the strain energy release rate (SERR) along the pre-crack perimeter during crack initiation and early propagation. However, they had only a minor effect on the stiffness after full fiber bridging development in all directions. The plates finally achieved constant stiffness, which increased linearly with the fracture resistance. The final crack shape was dependent on the loading zone shape and area, but the effects were relatively weak.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•Fatigue experimental investigation of cold-curing structural adhesives.•Wet, dry, and dried specimens were investigated.•Fatigue life up to 10million cycles was reached.•Plasticization due to water ...uptake reduces fatigue experimental scatter.•Drying after saturation improves fatigue life.
This paper presents the results of an experimental program designed to study the effects of aging and a wet environment on the fatigue behavior of epoxy resins used in bridge applications. Specimens were manufactured, cured, and treated, before the experiments, under a variety of conditions, in room and in water environments, in order to simulate the aging of adhesives in bridges for a period of up to 100years. Experimental results indicated that a typical power law S-N equation could describe the fatigue stress vs. life behavior of the examined material under different gravimetric conditions. The slope of the curve was found to be in the range of that of other polymers and polymeric composite materials. The cyclic strain behavior and hysteresis loops were obtained under different gravimetric conditions and at different stress levels and the effects of both parameters on the viscoelastic behavior of the material have been thoroughly discussed. The fatigue failure surfaces were also recorded using a digital handheld microscope to reveal the damage mechanisms. The results of this work showed that the examined epoxy resin could sufficiently sustain fatigue loads with maximum cyclic stress levels of more than 25% of their quasi-static strength for more than 2million cycles.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
•Investigates quasi-static and fatigue behavior of hybrid composites.•Compares glass/carbon with low/high stiffness carbon/carbon hybrids.•Discusses the pseudo-ductile behavior of the ...specimens.•Shows that DIC can be used for the damage progress monitoring.
This work investigates the quasi-static, low-cycle and fatigue behavior of hybrid glass/ultra-high modulus carbon (GC) and low modulus/ /high modulus carbon (CC) fiber composites. These pseudo-ductile unidirectional interlayer hybrids are a new type of composites whose potential is not yet fully understood, particularly under cyclic/fatigue loading. Different test methods (digital image correlation, video extensometer and thermal camera) were used to record the evolution of the strain, damage and temperature during loading. The results of quasi-static loading shown pseudo-ductile responses with multiple fractures for all the series. The CC specimens exhibited higher initial elastic modulus, ‘yield’ stress and strength, while the GC specimens showed the highest pseudo-ductile strain. Much higher capacity of CC to resist to fatigue loading was observed. In the GC specimens significant damage was accumulated during fatigue loading, when the damage evolution of multiple fractures in different layers developed to delamination between the glass and carbon layers.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
The tension–tension fatigue behavior and damage mechanism of basalt fiber-reinforced epoxy polymer (BFRP) composites at different stress ratios are studied in this paper. The fatigue experiments were ...performed under stress ratios,
R
=
σ
min
/
σ
max
of 0.1 and 0.5, while the lifetime and the stiffness degradation were monitored and analyzed to investigate the effect of stress ratios. The damage propagation during fatigue loading was periodically monitored by using an in situ scanning electron microscope (SEM). The results show that the fatigue life decreases and the fatigue life degradation rate increases with the decrease of stress ratio for examined BFRP composites. The stiffness degradation is also sensitive to different stress ratios, showing a greater stiffness loss before failure at lower stress ratio. From the SEM images, it is indicated that the micro-damage mode shifts from interface debonding and matrix cracking into fiber breaking with decreasing stress ratios.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, SIK, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
•Creep-fatigue interaction in (±45)2s glass/epoxy composite laminates was studied.•Fatigue loading was interrupted by creep at the maximum stress level.•Fatigue behavior was affected by hold loads ...(creep).•Damage was observed at the early stages of pure creep.•Fatigue damage accelerated the creep strain development during the hold time.
Angle-ply (±45)2S glass/epoxy composite specimens have been subjected to pure creep and tension-tension constant amplitude fatigue loading interrupted at σmax by creep intervals lasting for 2 or 48 h in order to examine the effects of creep loading on the fatigue response and vice versa. The specimens’ behavior and damage status were continuously monitored during the experiments; strains were measured by a video extensometer, the self-generated temperature on the specimens’ surface was recorded by an infrared camera, while a digital camera with sufficient backlighting was used in order to capture the damage development in the translucent specimens throughout the experiment. Post-mortem photos were taken by a digital microscope for the analysis of the fracture surfaces. In comparison to continuous fatigue, applying the creep-fatigue loading pattern with a 2-h creep time at low stress levels had no effect on fatigue life. However, as the stress level increased, specimen stiffening occurred during creep loading because of the glass fiber realignment, which also decreased the internal friction, hysteresis loop area, and self-generated temperature, thus prolonging the fatigue life. The restoring of fatigue stiffness was greater at a creep time of 48 h due to more creep strain, which led to more fiber realignment. However, the higher creep strain at high stress levels caused more creep damage and thus resulted in a shorter fatigue life. In addition, it was observed that the fatigue damage accelerated creep deformation.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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•Thin PEI and PVDF interlayers (IL) arrest mode-I crack in epoxy materials.•Finite element models predict crack tip shielding by these toughened interlayers.•Initial toughness & ...stiffness are influenced by epoxy-IL compatibility.•Crack-reinitiation load is increased up to 2.5 times.•Energy absorption is enhanced up to 43 times.
This work examines the crack-arresting capability of PEI and PVDF thermoplastic interlayers in short-glass fiber modified and core–shell rubber toughened epoxy materials under mode-I fracture loading. Experimental results show that the initial crack can be effectively arrested by the thermoplastic-epoxy interface and reinitiation of this crack at the thermoplastic layer requires up to 2.5 times higher load than the crack initiation load of the pristine epoxies. The interlayered designs also exhibit a significant increase in energy absorption by up to 43 times more than their pristine counterparts. Competing damage mechanisms and failure events are captured by microscopy images, digital image correlation and high-speed photography observations. Additionally, elasto-plastic fracture mechanics models based on configurational material forces theory are developed for a preliminary crack-arresting material selection and to elucidate the material inhomogeneity effects.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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