With the development of science and technology, composite materials are widely used in aerospace, automotive, shipbuilding, construction, and other fields due to their excellent properties such as high strength, light weight, and corrosion resistance. However, composite materials often face a key issue during use - insufficient interlaminar strength. Interlaminar strength refers to the size of the bonding force between the layers of composite materials and is an important factor affecting their overall performance and service life. Therefore, accurate testing and evaluation of the interlaminar strength of composite materials is of great significance.

　　Currently, there are mainly the following methods for testing the interlaminar strength of composite materials:



1. Short Beam Shear Test



This method causes the sample to bear shear forces under a three-point bending loading, with the sample experiencing shear action under a smaller span. Due to its simplicity of operation and small sample size required, it is often used for the preliminary evaluation of the interlaminar shear strength (ILSS) of composite materials. However, the results are influenced by various factors such as span-to-thickness ratio and fiber orientation, and are therefore usually used only for relative comparison.

　　2. Iosipescu Shear Test



This method measures the shear properties of the material by applying an asymmetric load to a V-notch sample. The Iosipescu test can accurately determine the interlaminar shear strength and is suitable for anisotropic materials. Its advantage lies in avoiding the tensile or compressive interference that may occur in other methods, providing a purer shear state.



3. Double Cantilever Beam Test (DCB)



This method is used to measure the interlaminar fracture toughness of composite materials. By introducing an initial crack in the middle of the sample and applying a load, the crack propagation is observed. The DCB test can effectively evaluate the material's resistance to destruction during crack propagation and is widely used in structural health monitoring and life prediction.



4. Interlaminar Tensile Test and Interlaminar Shear Test



Directly testing the interlaminar tensile and shear strengths is also a method. By using specific fixtures and sample designs, loads are applied vertically or parallel to the lamination direction to evaluate the interlaminar bonding strength. This method requires high standards for fixture design and loading methods, but the results are more intuitive and reliable.



In addition, with the development of testing technology, non-destructive testing techniques such as digital image correlation (DIC) and acoustic emission detection are also widely used in interlaminar performance evaluation, providing strong support for the research on the damage evolution and failure mechanisms of composite materials.



In summary, there are various testing methods for the interlaminar strength of composite materials, each with its own advantages and disadvantages. The appropriate method should be selected according to actual needs and testing conditions. In the future, with the development of advanced materials and testing equipment, interlaminar strength testing will become more accurate and efficient, providing a solid technical guarantee for the design and application of composite materials.