Tension Fatigue Behavior Research Articles

Tension–Tension Fatigue Behavior of Ribbed Glass Fiber–Reinforced Polymer Bars in Air

Tension–Tension Fatigue Behavior of Ribbed Glass Fiber–Reinforced Polymer Bars in Air

Experimental and numerical investigation on tension–tension fatigue behavior of three-dimensional five-directional hybrid braided composites

This paper presents an experimental and numerical investigation on tension–tension fatigue behavior of hybrid carbon/glass three-dimensional five-directional (3D5D) braided composites. Fatigue tests were carried out under the stress ratio of 0.1. The experimental results show that the fatigue strength significantly decreases as the fatigue life increases and the stiffness gradually decreases as the loading cycles increase. The fatigue life at the stress level within 35 %–50 % ultimate tensile strength (UTS) is within 4 × 103–6 × 105 cycles. The stiffness degradation before failure increases from 39 % to 58 % as the fatigue stress decreases from 50 % UTS to 35 % UTS. Under tension–tension fatigue loading, matrix cracking inside the yarns and interfacial debonding between the yarns and the matrix firstly occur and propagate, then matrix cracking appears in the resin-rich regions and numerous fiber breakage happens until final failure. The fatigue performance and damage mechanisms of braided composites are affected by fiber hybrid mode and braiding methods. Additionally, a mesoscale representative volume element (RVE) model with periodic boundary conditions and a progressive fatigue damage model was developed for the 3D5D hybrid braided composites. The numerical simulation results of fatigue life, stiffness degradation and damage progression have good agreement with experiments, demonstrating the validity of the developed model.

Effect of fiber architecture on tension–tension fatigue behavior of bolted basalt composite joints

The effect of fiber architecture, i.e., unidirectional (UD) vs. multi-directional (MD), on the tension–tension fatigue behavior of bolted double-lap basalt composite joints was experimentally investigated. The fatigue load-life (F-N) curves of MD and UD bolted joints were established and fatigue degradation was characterized by cyclic displacement, cyclic energy dissipation, cyclic stiffness, and self-generated heat. The failure mechanisms and fatigue life of MD and UD bolted joints during fatigue were discussed and further compared to similar adhesively bonded joints. The results showed that the MD bolted joints exhibited much longer fatigue life than UD bolted joints, however, the rapid damage initiation and propagation in the former led to a slightly steeper slope of the F-N curve. The fatigue life of the MD bolted joints was much shorter than that of the bonded joints mainly due to the lower static resistance of the former. However, the slope of the F-N curve of the MD bolted joints, resulting from fiber-dominated fatigue damage, was much flatter than that of the bonded joints caused by polymer-dominated creep-fatigue interaction.

Life assessment of thermomechanical fatigue in a woven SiC/SiC ceramic matrix composite with an environmental barrier coating at elevated temperature

In this work, the tension–tension fatigue behavior of a woven SiC/SiC ceramic matrix composite with an environmental barrier coating is investigated under elevated temperatures up to 1300 °C. Experimental investigations reveal the fatigue failure mechanism for SiC/SiC CMCs with EBCs under on-axis and off-axis loading conditions, and the materials undergo cyclic softening throughout the loading history. A mechanism-based framework is proposed to interpret the fatigue behavior of CMCs through detailed fatigue experiment observations. Based on the decrease in the elastic modulus of the composites, a new fatigue damage model is developed to characterize the fatigue damage evolution and assess the fatigue life of woven SiC/SiC CMCs with EBCs. The good agreement between the proposed model and experimental data indicates that the damage model has the potential to describe complex thermomechanical damage of SiC/SiC CMCs with EBCs under thermomechanical loading.

The tension–tension fatigue behavior of carbon fiber/epoxy woven composites with stable structural reinforcements

AbstractCarbon fiber/epoxy woven composites with stable structural reinforcements exhibit a better static mechanical property than composites with unstable reinforcements. The stable structural reinforcements show a limited deformation during the curing process. To investigate the influence of reinforcements on the tension–tension fatigue properties of composites, three typical composite samples were manufactured and experiment research was developed. The results show that the composites with stable structural reinforcements prove excellent fatigue behavior, and the initial elastic modulus can be enhanced. The curvature of load‐bearing yarns affected the loading capacity, and the low curvature improve the structural integrity. The unstable structural reinforcements lead to the “fatigue strengthening” after a limited number of cycles, owing to the straightening of load‐bearing yarns. Reducing the curvature of yarns can effectively decrease the occurrence of initial cracks by altering the structural characteristics of reinforcements, which strengthens the bonding to improve fatigue resistance.

Effects of hybridization on the tension–tension fatigue behavior of continuous-discontinuous fiber-reinforced sheet molding compound composites

This study is focused on the fatigue of sheet molding compounds (SMC) with a discontinuous (DiCo) glass fiber-reinforced core and continuous (Co) unidirectional ([0/DiCo/0]) or cross-ply ([0/90/DiCo/90/0]) carbon fiber-reinforced face layers. Tension-tension tests were conducted on the constituents (i.e., DiCo and Co SMC) and hybrid specimens. Hybridization effects were larger under cyclic than under monotonic loading. Constraining effects resulted in enhanced high fatigue strength of the Co plies in [0/DiCo/0]. [0/90/DiCo/90/0] was more sensitive to fatigue than [0/DiCo/0] due to localized damage starting from 90°-ply cracks. The S-N behavior of the hybrid was approximated from the behavior of DiCo SMC.

Tension–tension fatigue behavior and residual strength evolution of SiC/(PyC/SiC)2/SiC minicomposites prepared by CVI+MI and CVI+PIP processes

The residual tensile strength (RTS) evolution of SiC/(PyC/SiC)2/SiC samples, prepared by chemical vapor impregnation (CVI) combined with either melting reaction sintering (MI) or polymer impregnation and pyrolysis (PIP), was investigated after 106 cycles as the pre-fatigue stress increased. The fatigue limits of the two tested specimen types, CVI + MI and CVI + PIP, were 760 and 660 MPa, respectively, corresponding to 95% and 75% of the tensile strength, respectively. Although the RTS of the two specimen types first increased and then decreased, it was interesting that after pre-fatigue, the maximum RTS of the CVI + PIP-prepared sample at 680 MPa, was 16 MPa higher than that of the CVI + MI-prepared sample at 590 MPa. The nanoindentation results indicate that the matrix prepared by CVI could protect the fiber from heavy damage in subsequent preparation, and the matrix modulus and hardness were higher in samples prepared by PIP than those prepared by MI. According to the microstructure observations and hysteresis characteristics, it was concluded that the differences mainly came from the internal stress state, matrix, and fiber properties.

Improving the stress-controlled fatigue life of low solid-solution hardening Ni-Cr alloys by enhancing short range ordering degree

The tension–tension fatigue behavior of low solid-solution hardening Ni-Cr alloys with an approximately constant stacking fault energy was systematically investigated under different stress amplitudes. With an enhancement of short range ordering (SRO) degree, the fatigue crack initiation mode is evolved from intergranular cracking to slip band cracking, and the cyclic deformation mechanism changes from wavy to planar dislocation slip. Both the fatigue strength coefficient (σ′f) and exponent (b) can be simultaneously increased by inducing SRO structure that greatly enhances the cyclic strain hardening capacity, deformation homogeneity and slip reversibility, and the fatigue life is thus significantly improved.

Elevated temperature effect on tension fatigue behavior and failure mechanism of carbon/epoxy 3D angle-interlock woven composites

This paper reported elevated temperature effect on tension fatigue behavior and failure mechanism of carbon/epoxy 3D angle-interlock woven composites. The S-N curve shows that the composite has good fatigue properties, and the fatigue properties decrease to a certain extent at elevated temperature. The tensile fatigue limit of composite is 38% and 30% stress level at 25 °C and 100 °C, respectively. Tensile modulus-fatigue life curve shows that the composite has obvious three-stage cumulative damage development, while the high temperature increases the material’s viscoelasticity and toughness. Fracture morphologies indicate that the composite exhibits jagged inclined fracture. The main fatigue failure mechanism is matrix microcracks propagate and expand inside the material along warp and weft direction. The microcracks propagate to the fiber/matrix interface, resulting in stress concentration and debonding of the interface. And the fracture of a large number of warp fibers and fiber bundles eventually causes the composite to fail. At high temperatures, the material softens, the interface bonding strength becomes worse, leading to more serious fiber pullout and breakage, and the brittleness of the material weakens.

Tension-tension fatigue life estimation of CFRP composites by modal testing

This study investigates the tension- tension fatigue behavior of carbon/epoxy laminates under constant amplitude loading. Workpieces were prepared as per with fiber orientation of 45˚ were tested at different stress levels, for R = 0.1 with a frequency 5 Hz. The overall stiffness reduction was evaluated in terms of natural frequency by using modal testing. The modal testing was applied at specific intervals by interrupting the fatigue testing. It is shown that modal testing a Nondestructive testing (NDT) method can be applied to the fatigue life stimation of CFRP laminates. Curve fitting technique was used for developing an empirical model for prediction of fatigue life of CFRP components. The experimental results found good agreement with the model results. From the experimental results it was concluded that the modal testing is useful as a NDT for estimation of fatigue life, natural frequency reduction model is capable of representing the overall stiffness reduction due to fatigue. Change in damping ratio (ζ) is more significant than change in natural frequency due to fatigue.

Comparisons of tension–tension fatigue behavior between the 3D orthogonal woven and biaxial warp-knitted composites

In this article, the tensile fatigue properties of 3D orthogonal woven composites (3DOWCs) and biaxial warp knitted composites in 0°, 30°, 45°and 90° directions were studied and compared experimentally. The quasi-static tensile test and tension–tension fatigue test were carried out to obtain the stress–strain curves, the S–N curves and stiffness degradation curves. The results indicate that the two types of composites both exhibit greater stress in 0° and 90° directions and greater strain in 30° and 45° directions. The S–N curves obtained by experimental fitting can better reflect the fatigue degree of the two composites. The stiffness degradation rate of 3DOWCs is much higher than that of biaxial warp-knitted composites except in the 90° direction. The aim of this study is to provide a theoretical study for two kinds of composites to ensure the longest service life in practical applications.

Thickness-Dependent Mechanical Behavior of 〈111〉-Oriented Cu Single Crystals

To explore the dependence of mechanical behavior on the crystal size, the $$ [\bar{1}11] $$-oriented Cu single crystal was selected as a target material, and the variations of tensile and tension–tension fatigue behavior with the crystal specimen thickness (t) were systematically investigated. The results show that, with the decrease of t, the tensile yield strength continuously increases, especially as t < 0.4 mm, which is related to an enhanced role of surfaces in affecting dislocation activity; ultimate tensile strength first increases and elongation has almost no change as t is decreased from 2.0 to 1.0 mm, but with continuously decreasing t, both of them decrease; as t = 0.1 mm, the slight increases in ultimate tensile strength and elongation occur. With the decrease of t, the corresponding dislocation structures are evolved from the cell walls into the cells and tangles; meanwhile, the density of slip bands (SBs) decreases. Moreover, the obvious concentrated SB regions and notable cross-slip traces are clearly observed in thicker crystals. The fatigue life has no notable change as t = 2.0 and 1.0 mm, but increases subsequently with decreasing t due to the decrease in the plastic strain accumulation together with an enhanced interaction between the dislocations in the surface zone.

Temperature effect on fatigue behavior of basalt fiber‐reinforced polymer composites

In this study, the temperature effect on the static and tension–tension fatigue behavior of basalt fiber‐reinforced epoxy polymer (BFRP) composites is investigated. The S–N curves, energy dissipation, stiffness degradation, and displacement increment with lifetime under temperatures of −20, 0, 20, 40, and 60°C were derived to evaluate the BFRP fatigue performance under different environmental temperatures. The results showed that the static strength and fatigue life at a certain maximum stress increased with decreasing temperatures. This effect of temperature on the fatigue life was more pronounced at the low cycle fatigue regime. Life differences between the various temperatures became smaller with higher life. While energy dissipation was small for all specimens, the stiffness degradation and permanent displacement increment were sensitive to different temperatures, showing a greater lifetime stiffness loss and permanent displacement increment before failure at lower temperatures. POLYM. COMPOS., 40:2273–2283, 2019. © 2018 Society of Plastics Engineers

Effect of stress ratios on tension–tension fatigue behavior and micro-damage evolution of basalt fiber-reinforced epoxy polymer composites

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 = σmin/σmax 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.

Fatigue behaviour assessment of flax–epoxy composites

The present study focuses on the characterisation and evaluation of the fatigue behaviour of flax–epoxy composites. A better understanding of this behaviour allows the prediction of long-term properties to assess the viability and long-term durability of these materials. The purpose of this work is to systematically compare the tension–tension fatigue behaviour of flax fibre composites for one random mat, six textile architectures and two laminate configurations, which are used in a wide range of applications. The fibre architecture was found to have a strong effect on the fatigue behaviour, where higher static strength and modulus combinations present the best fatigue characteristics. They have a delayed damage initiation and increased fatigue life as well as a reduced damage propagation rate combined with higher energy dissipation in the early stages of fatigue loading.

Tension-tension fatigue behavior of a PIP SiC/SiC composite at elevated temperature in air

The tension–tension fatigue behavior of a PIP Silicon Carbide/Silicon Carbide (SiC/SiC) composite was investigated at 1300°C in air. The composite consisted of a new precursor polymer (LPVCS) pyrolyzed SiC matrix reinforced with pyrolytic carbon (PyC) coated 3D braided KD-I SiC fibers. Environmental barrier coatings (EBC) were employed to enhance the durability and air oxidation resistance of the composite at high temperature. Tension–tension fatigue tests were conducted at 1300°C in laboratory air at frequency of 1Hz. The ratio of minimum stress to maximum stress was 0.1, with maximum stresses ranging from 40 to 120MPa. Fatigue run-out was defined as 105 cycles. Strain accumulation with cycles and modulus evolution with cycles were analyzed for each fatigue test. Fatigue limit of SiC/SiC composite with EBC was 60MPa which was slightly higher than that without EBC. The microstructure as well as damage and failure mechanisms of the composites were investigated.

Influence of nanorubber toughening on the tensile deformation and tensile fatigue behaviour of a carbon fibre-reinforced epoxy composite

This study investigates the effect of nanocarboxylic acrylonitrile butadiene rubber on the tensile fatigue behaviour of carbon fibre-reinforced polymer composites with dicyandiamide-cured epoxy matrix. The stress-controlled tension–tension fatigue behaviour at a stress ratio of R = 0.1 and maximum stresses between 400 MPa and 650 MPa was investigated for the case of carbon fibre-reinforced polymers with pristine and nanorubber-modified epoxy matrices with loadings of 5 phr, 10 phr, 15 phr and 20 phr. The results from the experimental tests show that the high-cycle fatigue life of the laminates with 15 phr of nanorubber-modified resin matrix was increased by a factor of two compared to the pristine matrix samples. Scanning electron microscopy images of the fracture surfaces also show an enhanced plastic deformation existing at the fibre–matrix interface and a lower extent of fibre pull-out; both contributing towards the enhancement of the fatigue performance of the carbon fibre-reinforced polymer composites.

Open hole quasi-static and fatigue characterisation of 3D woven composites

This paper presents a comprehensive study on the open-hole quasi-static tensile and tension–tension fatigue behaviour of an orthogonal and an angle-interlock 3D woven carbon/epoxy composite. The full-field strain distribution during quasi-static tests was characterised using digital image correlation (DIC), and the fatigue damage behaviour was monitored using an infra-red camera. The notched tensile strength was less than 17% lower than the un-notched tensile strength and not very sensitive to the notch size. The fatigue specimens were loaded with maximum stress of about 60% of the ultimate failure stress and no complete fracture occurred after 5,000,000 cycles. The residual fatigue strength was also found to be similar to the quasi-static tensile strength in both weaves. The surface crack initiation and progression during fatigue loading was identified using thermoelastic stress analysis which revealed that the orthogonal weave had larger surface damage area than the angle-interlock weave.

Effects of combustion and salt-fog exposure on fatigue behavior of two ceramic matrix composites and a superalloy

Tension–tension fatigue behavior of two ceramic matrix composites (CMCs), SiC/SiC (Nicalon™/SiC) & oxide/oxide (Nextel™720/AS), and a superalloy (Rene 41) was characterized under combustion environment as well as under alternate salt-fog exposure for 4 h and combustion fatigue for 6 h. The run-out limit was 25 h (90,000 cycles) of fatigue. Test temperatures were 900, 1050, and 1050 °C for Rene 41, SiC/SiC, and oxide/oxide CMCs, respectively, and the applied maximum fatigue stress was 62 MPa. All three materials survived up to 25 h under combustion fatigue without any exposure to salt. Rene 41 and Nicalon™/SiC survived up to 25 h (90,000 cycles) under the alternate exposure of salt-fog and combustion fatigue. However, exposure to salt-fog exposure (5 wt%) had very detrimental effect on the combustion fatigue resistance of Nextel™720/AS. The reduction in salt concentration to 0.5 wt% had less detrimental effect. These tests were supplemented with more tests, where applied stress level, test temperature, and salt concentration were changed. Out of these three gas turbine engine materials, Nicalon™/SiC exhibited better fatigue performance in terms of applied temperature and stress level under combustion condition as well as when exposed to alternate salt-fog and combustion.

Tension–tension fatigue behaviour of woven flax/epoxy composites

Understanding the fatigue performance of biocomposites is critical in order to increase their acceptance, but current literature in this area is mostly limited to nonwoven reinforcements. This paper considers the tension–tension fatigue of three different woven flax/epoxy composites, for which two of them are prepreg-based and the other is manufactured using the Vacuum Assisted Resin Transfer Moulding (VARTM) process. Good fatigue performance of flax fibres comparable to those exhibited by glass fibres has shown the potential of this material to be implemented in load-bearing applications. The results suggest that minimizing the crimp in the yarns is a major concern to increase the resistance to fatigue damage in this class of materials. In addition to the three mentioned composites, two hybrids of flax/glass/epoxy were manufactured using the same VARTM process to check if the fatigue stability of flax fibre is extendable to its hybrids. The results show that an increase in the strength is possible, while maintaining similar fatigue behaviour as the plain flax/epoxy composites.