End reinforced test specimen

When studying material properties, it is typically necessary to fabricate a certain number of standard test specimens to conduct tests on properties such as tensile strength, compression, bending, torsion, shear, etc. A significant difference between 3D braided test specimens and those prepared using other techniques is that testing standards cannot be generalized. For instance, laminated composite specimens typically have a thickness of only around 0.1-0.2 mm due to the thin thickness of each ply (prepreg), resulting in a typical specimen thickness of 1-2 mm. In contrast, the internal structure of 3D braided composite materials consists of different cells formed by fibers in the internal, edge, and corner regions, with the internal cells being the dominating microstructural form and primary contributors to material properties.

In practical applications, taking rectangular specimens as an example, the surface cells on the two wide surfaces occupy a portion of the thickness. If the specimen is made very thin, only the properties of the surface cells may be representative. Therefore, to truly measure material properties, not just those of the surface cells, a sufficient number of internal cells are needed, resulting in thicker specimens. Alternatively, smaller yarns can be used to weave the specimens, but this approach brings limitations in terms of equipment, materials, and costs.

Typically, standard specimens braided with 6k or 12k carbon fibers are required to be 3-5 mm thick and have a width of 15-25 mm, making it difficult to obtain corresponding test results by simply bonding reinforcement patches at the ends. This necessitates the use of our company's patented technology to fabricate specialized 3D braided test specimens, especially for tubular specimens. Currently, using this technology, the axial tensile strength of T700-grade 3D woven composite material specimens exceeds 1700 MPa.