Strength characterization of glass/epoxy plain weave composite under different biaxial loading ratios

Abstract

Over the past years, various studies have been investigated in order to characterize the behavior of composite materials under different multi-axial loading conditions. One of the most used biaxial techniques is the in-plane biaxial test on cruciform specimens. To achieve reliable biaxial failure results, the design of the cruciform specimen presents a crucial part. Previous studies show that there is no well-adapted cruciform geometry for the composite biaxial tests. In this paper, an optimal cruciform specimen has been defined numerically for the composite characterization test. The specimen is composed of two aluminum tabs glued on top and bottom side of the plain-weave glass/epoxy composite. Finite element simulations have been carried out in order to study the influence of the aluminum grade and thickness on the stress distribution in the composite. An experimental validation confirms the failure of the specimen in the central zone under three different biaxial tensile ratios. The experimental strains were evaluated using the digital image correlation method. The traction/traction quadrant of the failure envelop was obtained and compared with different failure criteria. The maximum strain criterion shows a good agreement with the experimental results.

Investigation of Biaxial Properties of CFRP with the Novel-Designed Cruciform Specimens

“…Similarly, the ultimate tensile strength of the Y-axis under the biaxial tension can be found to increase first and then decrease with the increase in the X-Y load ratio compared to the Y-axis uniaxial tensile. This biaxial strengthening effect has been reported in the studies of biaxial tension of glass/epoxy composites [ 39 , 40 ]. The mechanism can be identified based on the shape of the highest-order failure theory predictions [ 41 ].…”

Advances in Cruciform Biaxial Testing of Fibre-Reinforced Polymers

“…However, there is a consensus in the research field to prefer the use of full-field techniques, emphasising the case of DIC, which has been applied, to date, in numerous biaxial tests with cruciform specimens [44,46,60,61,65,67,69,71,78,81,[83][84][85][86][87][88]. In addition to the detailed visualisation of the strain contours in different directions at every point on the surface, this technique provides numerous advantages.…”

“…In this way, the material to be tested must only be machined in its outer contour, and the tabs are machined in their central area, leaving the gauge zone accessible for measuring. This option is firstly described in the works by Kumazawa and Huang et al [42,81,120], and similarly reproduced in subsequent works by other authors [44,83,85,87,104]. Most of these works obtain the specimen by adhering the machined tabs on the contoured specimen, but Escárpita et al [104] performed a modification in the manufacturing methodology.…”

“…The first type failed prematurely, observing lower maximum stresses than other options, and a failure mode inappropriate for strength characterisation (i.e., failure is initiated outside the gauge region). Kobeissi et al [85] defended the use of aluminium tabs versus composite ones, due to the facility of machining metal, the risk of delamination on composite tabs and the capacity of withstanding larger strains, thanks to metal plasticity. Moreover, authors validated their design through numerical simulations based on FEM, including cohesive elements representing the adhesive layer between the composite specimen and the aluminium tab.…”

“…On the other hand, this radius is limited due to manufacturing constraints. Finally, Kobeissi et al [85] investigated the machining of aluminium tabs with linear and curved transitions, concluding that the curved transition could postpone the failure outside the gauge zone. Despite all of the above, other studies proposed specific approaches for certain materials or load states.…”