Time‐dependent failure of off‐axis loaded unidirectional glass/iPP composites

Abstract

In our previous study, we demonstrated that the time‐dependent failure of transversely loaded UD (unidirectional) glass/iPP is fully plasticity‐controlled and proposed a lifetime prediction method based on plasticity to predict transverse failure. In the present work, extending our previous study to other off‐axis angles, we aim to investigate the effect of the off‐axis angle on the time‐dependent failure of UD glass/iPP, and to propose a lifetime prediction method for the off‐axis failure. Glass/iPP specimens with different off‐axis angles are tested at various strain rates, creep, and fatigue loads to characterize the anisotropic, time‐dependent mechanical response. It is demonstrated that the influences of strain rate and fiber orientation angle on tensile strength are multiplicatively separable; also referred to as factorizable, enabling one to characterize the angle dependence at a single strain rate and the strain rate dependence at a single angle. Moreover, similar to transverse loading, off‐axis failure is also observed to be plasticity‐controlled. Based on these observations, the lifetime prediction method for the plasticity‐controlled transverse failure is extended to off‐axis loading using the aforementioned factorazibility, which resulted in lifetime predictions in agreement with the experimental creep and fatigue data.

Matrix dominated failure in continuous carbon fibre reinforced poly(ether ether ketone)

“…However, on switching to a double logarithmic scale, it becomes evident that the strain rate dependence for all loading angles become parallel, as shown in Figure 3.15 (b). Similar observations have been reported for SF glass/PC, long fibre glass/iPP and SF C/PEEK [57], SF glass/PA-6 [77] and UD glass/ iPP [78] under off-axis loading. These studies suggest that the strain rate and angle dependence are factorizable and can be multiplicatively decomposed as follows:…”

“…This finding indicates that the matrix material is the dominant factor in determining the strain rate dependence of off-axis loaded composites, regardless of whether they are short or continuous fibre reinforced. Moreover, this observation is not limited to PEEK systems, as similar trends were reported for isotactic polypropylene (iPP) systems [78] as well. This observation might indicate a potential benefit to first understand and characterize the behaviour of the matrix without any reinforcements, which in principle could be less time consuming and straightforward in most cases.…”

“…It is observed that except for 𝜃𝜃 = 90° (𝜀𝜀 𝑐𝑐𝑐𝑐 = 0.001), all other loading angles display the same value of 𝜀𝜀 𝑐𝑐𝑐𝑐 = 0.008. This can be directly correlated with the fact that the strain at failure for other off axis angles is considerably higher due to shear deformations caused by extensive shear coupling, which is absent for transversely loaded composites [78]. In general, a good agreement between the data and solid lines is observed for all the loading angles in Figure 3.…”