Behaviour of rectangular z-pins for translaminar reinforcement of fiber reinforced plastics under dynamic loading

• Applicant: Professor Dr.-Ing. Gerhard Scharr
• Subject Area: Plastics Engineering ; Lightweight Construction, Textile Technology ; Materials in Sintering Processes and Generative Manufacturing Processes
• Term: from 2012 to 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 210369099

Fiber reinforced plastics (FRP) offer, because of their microstructural construction of load-bearing fiber materials and the shaping matrix very good mechanical properties in the plane of the laminate. In contrast to this a structure made of FRP loaded perpendicular to the plane of the laminate shows inferior mechanical properties. Especially shock or impact like loads often lead, because of the low impact strength and the associated susceptibility to delamination as well as the low damage tolerance, to a reduction of the residual strength. FRP structures are often built up of pre-impregnated semi-finished products, known as prepregs. The only approved method to improve them in impact resistance, delamination behavior and damage tolerance is the so-called z-pinning method at which thin pins are introduced in the component in the z-direction before curing. Z-pins are needle-shaped, usually round bars with diameters of typically 0.1...1.0 mm. Numerous studies have shown that the z-pinning is a very effective method to increase impact vulnerable structures. The goal of the project is the investigation of fiber reinforced composites reinforced with rectangular z-pins under dynamic loading. This project represents the logical continuation of the previous project which concentrated on the study of non-circular z-pins for translaminar reinforcement of fiber reinforced plastics. Experimental and numerical investigations revealed that rectangular pins, because of their greater surface area, have an improved interaction with the surrounding material and thereby turn out as much more effectively to improve the interlaminar properties and increase the damage tolerance of a FRP-structure. Due to their relatively sharp edges rectangular z-pins are suspected to induce stress peaks in the material and thereby reduce the fatigue strength compared to structures reinforced with round pins. Via experimental studies and FE analysis statements should be made whether the positive results from the previous project can be transfered on dynamic stress, whether and how the geometry of the pins affect the fatigue strength and which geometry is an optimal solution in terms of the mentioned problems.

• DFG Programme: Research Grants