In situ damage mechanisms investigation of PA66/GF30 composite: Effect of relative humidity

Abstract

is an open access repository that collects the work of Arts et Métiers ParisTech researchers and makes it freely available over the web where possible. b s t r a c tDamage mechanisms of injection molded polyamide-66/short glass fiber 30 wt% composite (PA66/GF30) were analyzed using in situ SEM mechanical tests on specimens conditioned under three relative humidity contents (RH = 0%, 50% and 100%). The validity of these in situ analyses was confirmed by Xray micro-computed tomography (lCT) observations on tensile loaded specimens. Experimental results demonstrated that relative humidity (RH) conditions influence strongly the damage level and damage mechanisms. Indeed, for specimen with RH = 0%, damage initiation occurs at significantly higher load level than those in RH = 50% and RH = 100% specimens. The higher relative humidity condition also results in higher damage level. Damage chronologies have been proposed as damage initiation in the form of fiber-matrix debonding occurs at fiber ends and more generally at locations where fibers are close to each other due to the generation of local stress concentration (for all studied RH contents), and first fiber breakages occur (RH = 0%). These debonded zones further propagate through fiber-matrix interface (for all studied RH contents), and new fiber breakages develop (RH = 0%). At high relative flexural stress, matrix microcracks appear and grow regardless the RH contents. For RH = 100%, these microcracks are also accompanied by many matrix deformation bands. Subsequently, they lead to the damage accumulation and then to the final failure.

Micromechanical Fatigue Visco-Damage Model for Short Glass Fiber Reinforced Polyamide-66

“…It is worth noting that fiber breakage will introduce two new oriented phases: broken fibers and subsequently coating of broken fibers. Figure 1 shows the RVE evolution in accordance with the previously identified damage mechanisms [1,2]. Furthermore, the fiber volume fraction for each orientation is estimated via Simpson's numerical integration of the experimental orientation density functions (ODF).…”

“…This accounts for the anisotropic nature of the nonlinear tangent modulus of the phases. The computed effective modulus of the homogenized material is recalled equation (1). This homogenization is here adapted to take into account the matrix nonlinear rheology, the composite microstructure and the damage evolution including fiber breakage, matrix microcracking and interfacial debonding.…”

“…Doghri et al [7] have developed a multiscale mean-field homogenization method to determine the effective properties of an elasto-vsiscoplastic matrix reinforced with elastic fibers, while Wu et al [20] have developed a model that account for the degradation of the material using a gradientenhanced damage model. For short glass fiber reinforced polyamide composites, damage mechanisms are strongly dependent on the material microstructure as well as hygrothermal conditions [1]. Such local damage mechanisms that depend on micromechanical fields need to be included in a multi-scale model to analyze the effect of the material microstructure on the fatigue life.…”

“…Damage mechanisms have previously been investigated by the authors [1,2] and by Cosmi and Bernasconi [5], using in-situ SEM tests and X-ray micro-computed tomography (µCT) observations. A damage scenario has been established, depending on the sample relative humidity.…”

Common Type of Damages in Composites and Their Inspections

“…Matrix crack, fiber-matrix debonding, and fiber breakage also happen during the impact or other kind of severe loadings in composites. Figure 5 illustrates these phenomena in composite structures [12] [13] [14].…”