Influence of patch length and thickness on strength and stiffness of patched laminates

Composite laminates made of fiber patches offer a large flexibility in terms of layup design. Geometrical layup parameters such as patch length and patch thickness are unique for this type of laminates. This article presents results on the investigation of the influence of patch length and patch thickness on the tensile strength and stiffness properties of patched laminates to contribute to the material understanding. The results show that an increasing of patch thickness leads to a drastic reduction in tensile strength of up to 48.7% for a triplication in patch thickness. The patch length was varied between 20 and 120 mm. Up to 60 mm, the tensile strength increased by 11.5%, further increase did not contribute to a further improved tensile strength. The influence of patch length and patch thickness on the stiffness was found to have only a minor effect. A three-dimensional numerical model that accounts for delamination failure using cohesive zone elements shows very good correlation with the experimental results. This shows its potential for virtual testing to determine tensile strength and stiffness properties of patched laminates without additional testing effort.