Development of a trace-based approach for elastic characterization of multi-material composite pipes: Theory and testing

Design of composite wrap pipes demands accurate experimental determination of the mechanical properties of the materials considered. The emphasis of this article is on the experimental characterization of the overall mechanical properties of the composite pipe through axial tension and internal pressure non-destructive tests. A stiffness matrix trace-based methodology is developed to determine the elastic properties of multi-material composite pipes (PVC liner + GFRP wrap) using only axial loading and internal-pressure tests. The approach identifies axial and hoop Young’s moduli and the axial/hoop Poisson’s ratios at the pipe level, and then infers the in-plane shear modulus from the invariant trace of the reduced stiffness matrix (Tsai modulus), as an alternative way to torsion test. Four nominally identical pipes were manufactured and tested in triplicate under axial tension, axial compression, and internal pressure. Despite identical constituents and processing, measurable variability was observed across pipes, underscoring the need for bulk, pipe-level characterization rather than extrapolation from coupon-level plies. Finite-element simulations using the identified properties reproduced the measured axial and hoop surface strains within the experimental 95% confidence bands for all load cases. The results demonstrate that the proposed, non-destructive, trace-based workflow provides accurate elastic properties for composite pipes while avoiding specialized torsion fixtures and specimen extraction.