A NOVEL MEASUREMENT METHOD OF TRACTION-SEPARATION RELATION FOR BI-MATERIAL DCB JOINTS
Topic(s) : Material and Structural Behavior - Simulation & Testing
Co-authors :
Shijie ZHNAG (CHINA), Jiacheng LIU , Wandong WANG (CHINA), Yu'E MAAbstract :
Adhesively bonded metal-to-composite bi-material joints are widely employed in aerospace engineering, which is attributed to improved weight saving, fatigue resistance and structural integrity of such joints. In-depth understanding of the fracture behavior of such joints is essential for structural safety design. The cohesive zone model (CZM) is an effective method for analyzing the fracture behavior of adhesive joints and composites. The core to CZM is its constitutive relation, namely traction-separation relation (TSR), which has been examined through various approaches, including the direct method and the inverse method. Nevertheless, these approaches exhibit drawbacks such as using pre-defined shapes that may deviate from reality, demonstrating low computational efficiency, and presenting challenges in achieving satisfactory convergence during calculations.
A new methodology on the basis of measuring outer strain distributions has been proposed for beam-like bi-material DCB joints to extract the TSR of CZM. This method relies on the calculations of the stresses acting on the faying interfaces of the two adherends and relative opening. The Timoshenko beam theory is employed to determine the deformation of the adherends subjected to the applied load and tractions from the adhesive deformation. To validate this methodology, a Finite Element Method (FEM) model with a pre-defined bi-linear TSR was adopted in Abaqus. The outer surface strain exported from the model was used in the proposed method to derive the TSL. The result shows a great consistency compared to the pre-defined TSR.
An experimental procedure has been carried out to study the CZM of TC4-CFRP adhesively bonded joints designed according to the so-called strain-based criterion (E1H12 = E2H22). The outer surface strain of the bi-material joints was measured by the distributed optical fiber sensor (DOFS) and then the proposed approach was employed to extract the TSR. In addition, the digital image correlation (DIC) method was also employed to monitor the crack tip opening displacement which was further used to derive the TSR on the basis of the J integral method. The two measured TSR based on different approaches were compared to verify the proposed method. The experimental results have shown that the TSR has been effectively identified by the proposed method.
It is found that the proposed method not only measures the TSR for the initiation phase, but also for the crack growth phase. The proposed method is easy to implement to measure the precise TSR of bi-material DCB joints.
A new methodology on the basis of measuring outer strain distributions has been proposed for beam-like bi-material DCB joints to extract the TSR of CZM. This method relies on the calculations of the stresses acting on the faying interfaces of the two adherends and relative opening. The Timoshenko beam theory is employed to determine the deformation of the adherends subjected to the applied load and tractions from the adhesive deformation. To validate this methodology, a Finite Element Method (FEM) model with a pre-defined bi-linear TSR was adopted in Abaqus. The outer surface strain exported from the model was used in the proposed method to derive the TSL. The result shows a great consistency compared to the pre-defined TSR.
An experimental procedure has been carried out to study the CZM of TC4-CFRP adhesively bonded joints designed according to the so-called strain-based criterion (E1H12 = E2H22). The outer surface strain of the bi-material joints was measured by the distributed optical fiber sensor (DOFS) and then the proposed approach was employed to extract the TSR. In addition, the digital image correlation (DIC) method was also employed to monitor the crack tip opening displacement which was further used to derive the TSR on the basis of the J integral method. The two measured TSR based on different approaches were compared to verify the proposed method. The experimental results have shown that the TSR has been effectively identified by the proposed method.
It is found that the proposed method not only measures the TSR for the initiation phase, but also for the crack growth phase. The proposed method is easy to implement to measure the precise TSR of bi-material DCB joints.