Experimental investigation on the mechanical behaviour of 3D carbon/carbon composites under biaxial compression

Abstract

The effects of complex state of stress on the compressive behaviour of 3D carbon/carbon composites are investigated by application of uniaxial and biaxial loadings using a specially developed Zwick cruciform testing facility. The shape of the biaxially loaded cruciform specimen is optimised to avoid premature fracture outside the gauge section. A semi-analytical method is proposed to determine the stress components in the gauge section of the biaxial specimen. The experimentally obtained failure stress relation, which traces an elliptical path in the principal stress space, can be well represented by the Tsai criterion with a stress interaction parameter of F 12 =-0.85. Macro-fracture morphology and SEM micrographs are examined and the results show that the failure mechanisms of the composites vary with the loading ratio. The results also suggest that the biaxial stress interaction effect is represented by a domain in the biaxial specimen, which is characterised by torsion and bending fractures in the dislocated fibres between two adjacent Z yarns.

Advances in Cruciform Biaxial Testing of Fibre-Reinforced Polymers

“…As a summary, the equipment with the best acceptance in the scientific community follows this same scheme of two orthogonal pairs of axially aligned actuators with independent load cells, whether they are electromechanical or hydraulic. Examples of similar facilities are found in [16,17,[41][42][43][44][45][46][47]. Hannon and Tiernan [48] reviewed the in-plane biaxial systems applied to the characterisation of sheet metal because biaxial states can be present in sheet metal forming processes and the interest of the biaxial response due to the anisotropy resulting in the material after manufacturing.…”

“…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]. An application that demonstrates the versatility of strain gauges is the ability to adhere them at both (top and bottom) surfaces of the specimen in such a way that they facilitate finding the bifurcation point caused by buckling by registering opposite trends in the measurement of strains resulting from the curvature of the specimen [45,75,76,78].…”

“…Authors agree on the special influence of the thickness of the central region, pointing out the contrast in the selection of this parameter, as it should be high enough to avoid instabilities, but small enough to guarantee high stress values in the biaxially loaded zone. Another solution to the problem of instability in slender arms of cruciform specimen is given similarly in the works by Manshadi et al [75,76] and Xu et al [45], removing the arms of the cruciform specimen and applying the compressive loadings directly over the central region. However, this could lead to increase stress concentrations close to the gauge zone.…”

Forming a defective surface layer when cutting parts made from carbon-carbon and carbon-polymeric composites

“…A study into mechanical properties of carbon composites [8] revealed the dependence of articles quality on the processes for their obtaining; however, the issues related to the impact of a force scheme acting on a material during machining remained unsolved.…”

Mechanical Fatigue Test of Aluminium Composite Panel (ACP) with Aramid Nida-Core Under Cyclic Bending

“…A dynamic mechanical analysis was used to characterize the storage modulus and loss factor. Xu et al investigate [14] the effects of complex state of stress on the compressive behaviour of 3D carbon/carbon composites by application of uniaxial and biaxial loadings using a specially developed Zwick cruciform testing facility. A semi-analytical method is proposed to determine the stress components in the gauge section of the biaxial specimen.…”