A novel fixture for determining the tension/compression-shear failure envelope of multidirectional composite laminates

Abstract

A new approach for biaxial loading of fibre reinforced composites is presented, based on the use of a Modified Arcan Fixture (MAF). In addition to combined tension-shear loading which can be achieved using a conventional Arcan fixture, the MAF allows the application of pure compression and compression-shear loading. Digital Image Correlation is used to obtain the full-field deformations of the specimens to establish the load response and failure behaviour for a range of multiaxial stress-strain states. The approach is demonstrated on glass/epoxy prepreg laminates. For unidirectional matrix dominated laminate it is shown that the failure envelope is described accurately by Puck's inter-fibre failure theory. For the multidirectional matrix-dominated laminate it is shown that the in-situ strength is much greater than that predicted using the unidirectional properties. The potential of the MAF for characterisation over the entire combined tension-shear and compression-shear domains using a single fixture is demonstrated.

A simple nonlinear constitutive model based on non-associative plasticity for UD composites: Development and calibration using a Modified Arcan Fixture

“…The aim of the present paper is to develop a nonlinear, pressure sensitive constitutive model for UD composites under in-plane multiaxial loading that can be fully calibrated using a Modified Arcan Fixture (MAF) and Digital Image Correlation (DIC) [16]. The MAF [17] is a novel biaxial test rig which can be used in a standard test machine to characterise UD composites in the full combined The front view of the MAF and the 'butterfly' specimen configuration used is shown in Fig. 2.…”

“…Further details on the MAF and the experimental set-up can be found in [17]. The MAF can subject the specimens to different combined tension/shear and compression/shear stress states by varying the pairs of loading holes (designated by the angle α).…”

“…Thus, by substituting Equations (18) into (17), all the plastic strain components can be evaluated based on the stress state alone. The yield parameters (H, J) and the hardening parameters (K, m)…”

“…5 are used to compute the compliance matrix C for each individual biaxial load case. The effective plastic strain increment, p d, can now be expressed as a function of H and J and based on the experimentally extracted plastic strain components upon rearranging the second and third rows respectively in Equation(17) to give:…”

“…by multiplying h(θ) with σx the yield function is retrieved.The individual plastic strain components in Equation A.2 can be substituted by the expressions given in Equation(17). Then the transformed stresses from Equation(20)and h() defined in Equation A.3 can be substituted and p  is obtained as a function of σx, h(), f(σij) and g(σij)Similarly, the effective plastic stress can be obtained as a function of σx as follows:Tobias Laux , Khong Wui Gan , Janice M. Dulieu-Barton , Ole T. Thomsen , A simple nonlinear constitutive model based on non-associative plasticity for UD composites: development and calibration using a Modified Arcan Fixture, International Journal of Solids and Structures (2018), doi: https://doi.org/10.1016/j.ijsolstr.2018.…”