Numerical and Experimental Analysis for Shape Improvement of a Cruciform Composite Laminates Specimen

Abstract

The use of composite materials has spread to different applications among which, those using thin sheet plates subjected to biaxial loads are commonly used in the car and aerospace industries. Hence, there is need of a reliable specimen to test these materials under biaxial loads. This reliability depends on measurements that are accurate and repeatable. Thus these measurements depend on the proper design of specimens. This paper reviews the development of cruciform specimens of carbon fibre composite materials and how the geometric shape has evolved. Based on this review, a new geometric shape is proposed. This improvement is based on numerical analysis of the specimen and tests results of experimental measurements carried out using a four piston rig in an orthogonal arrangement. Deformation is measured in the centre of the specimen using strain gauges. By obtaining the principal stresses, it was found that maximum stresses occur in the centre of the specimen.

Designing a Cruciform Specimen via Topology and Shape Optimisations under Equal Biaxial Tension Using Elastic Simulations

“…Shape optimisation of the specimen reduces the stress concentration at the intersection of the cross-arms, which is beneficial for preventing pre-failure outside of the gauge zone. Stress uniformity in the gauge zone is affected by the concentration of stresses at the cross-arm intersection [ 2 , 3 , 4 , 5 , 6 , 11 ]. Type C is slightly less uniform than type B in terms of the S 11 , S 22 , and S 12 distributions because the changes in boundary shape hinder the load transfer improved by topology optimisation.…”

“…The stress uniformity in the gauge zone of the cruciform specimen correlates with its structure [ 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 ]. The uneven stress distribution on the boundary of the gauge zone, and the stress concentration at the intersection of the cross-arms, deteriorate the stress uniformity in the gauge zone.…”

Fracture Behavior of a Unidirectional Carbon Fiber-Reinforced Plastic under Biaxial Tensile Loads

“…A cruciform specimen has been used for T-T loading tests on such laminates as cross-ply and angle-ply [ 26 , 27 , 28 , 29 , 30 ]. The present study applies this specimen to a unidirectional CFRP.…”

“…The present study applies this specimen to a unidirectional CFRP. According to these papers [ 26 , 27 , 28 , 29 , 30 ], conventional cruciform specimen shapes have a circular or square indentation referred to as ‘gauge area’ in the center. The authors also attempted to make this indentation and to fracture it at the center where the biaxial tensile load occurs, but it often broke prematurely at the arm.…”

Advances in Cruciform Biaxial Testing of Fibre-Reinforced Polymers

“…The referenced literature highlights the predominant use of strain gauges [17,[36][37][38][39][40][41]46,58,[72][73][74][75][76][77][77][78][79][80][81] which provides simplicity when recording the strain state in the gauge zone, in the absence of large strain gradients, such as open hole concentrators [60]. Another noteworthy advantage of the strain gauge technology is the need of a small space for its placement and wiring, which makes it an ideal technique for tests in which access to the specimen is limited [58,74,82].…”