Quantification Approaches for Fatigue Crack Resistance of Thermoplastic Tape Layered Composites with Multiple Delaminations

Automated tape placement with in-situ consolidation (ATPisc) is a layer-wise manufacturing process in which the achievement of proper interlayer bonding constitutes one of the most challenging aspects. In the present study, unidirectional carbon fiber reinforced thermoplastic laminates were produced following different manufacturing protocols using ATPisc. The interlayer bonding of the laminates produced was characterized by mode I fatigue fracture tests with double cantilever beam (DCB) specimens. Independent of the manufacturing approach, the laminates exhibited multiple cracking during DCB testing, which could not be evaluated simply following standard methods. Thus, various data analysis methodologies from literature were applied for the quantitative assessment of the fracture behavior of the laminate. The examination of the evolution of the damage parameter phi and the effective flexural modulus throughout testing enabled a better understanding of the damage accumulation. The Hartman-Schijve based approach was revealed to be a convenient method to present fatigue crack growth curves of laminates with multiple delaminations. Moreover, a preliminary attempt was made to employ a 'zero-fiber bridging' methodology to eliminate the effect of additional damage processes on the fatigue crack growth that resulted in large-scale, partially massive fiber bridging.

Automated summary

In this study, unidirectional carbon fiber reinforced thermoplastic laminates were produced using Automated Tape Placement with In-Situ Consolidation (ATPisc) and tested for interlayer bonding with mode I fatigue fracture tests. Various data analysis methodologies were applied to quantitatively assess the fracture behavior of the laminates, revealing the Hartman-Schijve based approach as a convenient method for presenting fatigue crack growth curves. Additionally, a 'zero-fiber bridging' methodology was attempted to eliminate the effect of additional damage processes on fatigue crack growth.