Stress ratio effect on tension-tension fatigue behavior of angle-ply GFRP laminates

Abstract

The effect of the stress ratio (R=σ min /σ max) on the fatigue behavior of (±45) 2S angle-ply glass/epoxy composite laminates was investigated by comparing their mechanical, thermal, and optical properties under the stress ratio of 0.5 with previous fatigue results obtained under the stress ratio of 0.1. When the stress ratio was increased from 0.1 to 0.5, the fatigue life was enhanced at the same σ max and the slope of S-N curve decreased, exhibiting more scattered responses. In addition, as the stress ratio increased, the fatigue damage was distributed more uniformly with a lower self-generated temperature at the same σ max. At R=0.5, fiber realignment, due to cyclic creep, increased the fatigue stiffness, thus compensating the decreasing effect of fatigue damage. At high stress levels, the stiffening effect dominated the stiffness evolution, resulting in greater fatigue stiffness with an increasing number of fatigue cycles; however, at low stress levels the degrading effect due to fatigue damage was prevalent. The stiffening effect led to smaller hysteresis loop areas at the beginning of the fatigue experiments, which subsequently stabilized for the greater part of the specimen fatigue life, followed by a slight increase before failure. At R=0.1, the fatigue stiffness decreased further and the hysteresis loop area became larger at all stress levels at the same σ max since the stiffening effect was less and fatigue damage more severe.

Transverse fatigue behavior analysis of symmetric and asymmetric glass fiber‐reinforced laminates

“…The type of the material was also found to play a crucial role in determining the degree of interaction between the cyclic creep and the fatigue damage as well as the dominance of one process over the other. [ 57 ]…”

Effect of stress ratio on the tension–tension fatigue behavior of tungsten carbide nanoparticles toughened GFRP

“…A similar enhancement effect has been observed due to an increase in stress ratio in the literature. 24 The tungsten carbide toughened GFRP panels (GFRP-WC) have shown an increase of about 4% for the FSC, and the FSE almost remains constant. By comparing the fatigue properties of GFRP with GFRP-WC specimens, it is noted that the FSC and FSE decrease by adding 2 wt.% of tungsten carbide to the GFRP laminates.…”

“…Increment in creep strain occurs with an increase in stress ratio, which is due to the progression of viscoelastic strain. 24 If the material undergoes loading at a stress ratio R = 1, which represents the pure creep loading condition, in this case, materials fail under creep. Therefore, as the stress ratio decreases from 1 to 0.1, creep strain decreases, which is due to the evolution of permanent strain.…”

“…Stiffness degradation and fatigue life estimation of adhesively-bonded joints based on experimental studies were presented by a few researchers. [20][21][22] Movahedi et al [23][24][25] presented the fatigue behavior of angle-ply glass/epoxy composite laminates under constant amplitude fatigue loading at different stress levels with a stress ratio of 0.1, 23 different stress ratio, 24 and creep effects 25 and reported that the damage was severe and localized at higher stress levels due to fiber pull-out failure. Ferdous et al 26 presented the effects of stress level, stress concentration, and frequency on the fatigue life of GFRP under tension-tension fatigue at a stress ratio of 0.1. and reported that failure was due to pure tension at high applied stress, while failure was dominated by stress concentration at a low stress level.…”

“…25 It is clear that different stress levels and stress ratios have a significant impact on fatigue processes such as cyclic creep, dissipated energy, and fatigue stiffness for GFRP laminates during their lifetime under tension-tension fatigue loading. 24 Also, the addition of nanoparticles into GFRP composite laminates modifies the fatigue stiffness and dissipated energy. 37,41 The objective of the current study is to investigate the fatigue behavior of woven ply GFRP laminates filled with tungsten carbide nano-powder at different stress levels by monitoring the fatigue stiffness, dissipated energy, and cyclic creep for different stress ratios.…”