An improved analytical method for calculating stiffness of 3D needled composites with different needle-punched processes

The mechanical properties of 3D needled composites are greatly associated with the complex needle-punched process. Needle-punched process is described quantitatively to relate with the internal features of 3D needled composites combining with experiment observations. The relationship between pinhole spacing and fiber breakage is established by Bayesian inference method and described by a probability function. Four kinds of internal needle-punched features whose local stiffness properties are calculated using an analytical method are distinguished. The stiffness properties of 3D needled composites are predicted analytically by using the volume fraction of each internal structural features based on the needle-punched process. The predicted results for 3D needled composites with different needle-punched processes are validated by the experimental results. This study can be used to construct the material design database for 3D needled composites with different needle-punched processes.