A new analytical method for determining J-integral-crack opening displacement curve of DCB specimen with large scale fiber bridging

• A new analytical method is proposed to calculate the J ( δ ) curve. • Damage onset parameters are directly extracted from the calculated J ( δ ) curve. • Multi-linear softening law is determined based on the calculated J ( δ ) curve. • Experimental cases with large scale fiber bridging length are studied. The fiber bridging is an important toughening mechanism, and J -integral theory is usually used to determine the bridging stress. To achieve the determination of bridging stress, the calculation of J -integral-crack opening displacement J ( δ ) curve is the key. A new analytical method is proposed to calculate the J ( δ ) curve, which only requires the experimentally recorded load–displacement data. Compared with the traditional analytical method based on equivalent crack length, the proposed method has more physical significance. Two independent parameters, i.e. initial fracture toughness J init and the crack opening displacement corresponding to initial damage δ 0 can be directly extracted from the calculated J ( δ ) curve. In addition, the bridging stress with a multi-linear function can be determined. Experimental cases with large scale fiber bridging are used to verify the validity of the analytical method. The proposed method is simple and effective, and can provide support for investigating the fiber bridging phenomenon of mode I delamination.