MMB Test of CFRP in Conformance with ASTM D6671

Carbon fiber reinforced plastic (CFRP) do not oxidize or rust and have a higher specific strength and stiffness than conventional materials. Applications of CFRP are being investigated, with a focus on applications as aircraft materials that require strength and durability. However, the superior mechanical properties of CFRP laminate are limited to a strengthened direction (parallel to fibers), and the strength of CFRP laminate is reduced significantly in directions that are not strengthened (interlaminar direction, for example.). CFRP laminate are also susceptible to impact, with out-of-plane impacts causing internal damage, such as peeling laminates, to CFRP laminate. The design and product development of CFRP laminate therefore incorporates damage tolerant design, which takes into consideration the effects of internal damage on the strength of the material. Damage tolerant design must determine how resistant a material is to interlaminar crack propagation, which is done by fracture toughness testing. For homogeneous isotropic materials, only fracture Mode I (crack opening mode) is evaluated normally in fracture toughness testing. Materials that are a composite of a resinous matrix and fibers are anisotropic, and it is important these materials are evaluated not just for fracture Mode I, but also for fracture Mode II (crack sliding mode), fracture Mode III (crack tearing mode), and mixed mode fractures. Mixed-mode bending (MMB) tests are used to evaluate fracture toughness in a mixed mode that combines Mode I and Mode II. Features of MMB testing are the mixed mode ratio (hereinafter referred to as mode ratio) can be changed on subsequent tests, and it is almost unchanged by crack propagation. While the stress intensity factor K is often used to evaluate the toughness of homogeneous isotropic materials, the interlaminar fracture that occurs in anisotropic composite materials is commonly evaluated using the energy release rate G, which is proportional to the square of the stress intensity factor K. 1) MMB testing was performed in conformance with ASTM D6671 and the total mixed-mode fracture toughness Gc was determined at four different mode ratios.

Content Type:
Application News
Document Number:
i257, LAAN-A-AG-E021
Product Type:
Material Testing, Universal / Tensile Testing
ASTM D6671, , Materials/Automotive, Carbon Fiber Reinforced Plastics, AGX-V Series Universal Electromechanical Test Frames, TRViewX Non-Contact Digital Video Extensometer
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