Effect of fiber array irregularities on microscopic interfacial normal stress states of transversely loaded UD-CFRP from viewpoint of failure initiation

Abstract

A detailed investigation has been carried out to determine the effect of local fiber array irregularities and controlling fiber distribution parameters on microscopic interfacial normal stress states for transversely-loaded unidirectional carbon fiber (CF)/epoxy composites. Linear elastic finite element analyses were carried out for two-dimensional image-based models composed of about 70 fibers. The relationship between the geometrical distribution of two adjacent fibers and the interfacial normal stresses (INSs) is 2 investigated for all fibers in different image-based models. Three boundary conditions for loading were selected: Case A involved cooling from the curing temperature (the difference in temperature was-155 K); Case B involved transverse loading of 75 MPa chosen as an example of macroscopic transverse fracture strength; and Case C involved both cooling from the curing temperature and transverse loading of 75 MPa. High compressive INSs due to the difference in the coefficients of thermal expansion are observed at the location of the shortest interfiber distance for Case A (cooling). High tensile INSs are observed at the location of the shortest interfiber distance and where the fiber alignment angle to the loading direction is small for Case B (loading). For Case C (cooling and loading), the high thermal residual compressive INSs and the high mechanical tensile INSs compensate each other, and the INSs at a short interfiber distance are much lower than those for Case B. These results clearly indicate the importance of the contribution of the thermal residual stresses to the transverse tensile failure initiation of CF/epoxy laminates.

A combined experimental–numerical approach for generating statistically equivalent fibre distributions for high strength laminated composite materials

“…2(a), the mean of the diameter distribution was found to be 6.6µm which implies that, for neighbouring fibres, the average inter-fibre spacing is in the region of 0.4µm-0.6µm. This minimal spacing between fibres has been shown by Hojo et al [4] to have a significant effect on the stresses developed at the fibre/matrix interface under certain loading conditions, which will affect the overall failure properties of the composite. This further highlights the importance of reproducing these characteristics in a micromechanical model.…”

“…Because of the nature of high volume fraction composites, fibres are forced to arrange themselves in close proximity to one another, commonly at distances less than 0.5µm. As shown in [4], this can result in a significant increase in the interfacial normal stresses being developed which is a key factor in transverse failure. Thus, the approach taken here uses experimentally measured nearest neighbour distribution functions to define the distances between fibres.…”

“…It was concluded that the use of periodic models could lead to an underestimation of matrix cracking and damage initiation and so the use of random models are needed when modelling failure and damage. Hojo et al [4] investigated the effect of local fibre distributions on the microscopic interfacial normal stress states for unidirectional carbon fibre epoxy laminates loaded in transverse tension. It was found that for an irregular fibre array the absolute value of the interfacial normal stresses rapidly increased when the distance between fibres was less than 0.5µm.…”

Multiscale Modeling of Advanced Materials for Damage Prediction and Structural Health Monitoring

“…Each of the three microstructures (ordered, semi-random, and hard-core) contains 100 fibers and periodicity of the fibers is enforced at the RUC boundaries. especially for values of r/rm less than three, correlates well with mechanical performance of a composite (Bulsara, Talreja, and Qu, 1999;Hojo et al, 2009). To further verify that the microstructures follow a convergent trend, the two-point correlation function was plotted for microstructures ranging from 0% disorder (ordered square packing arrangement) to 100% disorder (hard-core arrangement) in 10% increments.…”

The mechanical property prediction of fibre-reinforced composite materials based on a new generating random fibre distributions method

“…Hojo.M studied the local fibre distribution effect on the micro-interface normal stress of unidirectional carbon fibre epoxy laminates under transverse tensile loading and the results showed that the interface normal stress absolute value of fibre irregular distribution increased rapidly when the distance between fibres was less than 0.5μm [5] . Vaughan and McCarthy presented the nearest neighbour algorithm based on test data and its local shape distribution function was equivalent to the fibre distribution of real structure [6] .…”