UPWARDS Deliverable D5.4: Report and data on the effect of fatigue loading history on damage development

Fracture in laminated composites is typically caused by inter-laminar damage, such as
delamination, promoted by or coexisting with intra-laminar damage, like matrix-cracking and fibre
failure. During operation of composite structures, these damage mechanisms initiate and
propagate under variable amplitude loading conditions that are very different from the constant
amplitude loading conditions applied to test specimens in laboratories to characterise fatigue
properties of the material. The work in Task 5.4 focuses on the effect of variable amplitude loading
on the damage evolution in fiber reinforced polymer laminated composites. An experimental test
campaign investigates fatigue-driven delamination under multi-level block loading, and a new
crack growth rate model is proposed. The crack growth rate model is included in a finite element
formulation as an extension of the inter-laminar fatigue damage method from Task 5.1. The
method has been implemented in the Simcenter Samcef software. The simulated results from the
Simcenter Samcef solver show a significant improvement in the delamination growth prediction in
comparison to the conventional non-interaction crack growth rate model. Another experimental
campaign investigates intra-laminar damage under two-level block loading. The experiments
subject specimens to flexural fatigue loading using a simplified test configuration that can be
readily implemented by most any research group with access to a universal fatigue testing
machine. The simplified experimental setup used in this work was suitable to investigate the load
history effects on intralaminar damage evolution.