The critical forces, which were achieved from the 4PB experiments, were used to obtain the critical ERRs Gc (i.e. interfacial fracture toughness) of the interface between Cu leadframe and EMC. They were determined by the FEM simulations using the three mentioned methods: VCCT, VCE and J-integral. The verification of simulations was performed using an analytical solution (eq. (6)). Based on the critical ERRs obtained from different specimens tested at different temperatures, the temperature dependence of the interfacial fracture toughness was investigated. The upper EMC layer of the sample was notched with a diamond blade to get the depth of the notch, approximately 80% of the EMC thickness. Fig. 5.1 shows the 4PB test setup, and Fig. 5.2 shows
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Fig. 5.3 shows a typical load-displacement curve of the 4PB fracture test. The slope of the linear part of the curve corresponds to the stiffness of the whole structure. The peak force represents the required force for fracture of the upper layer (EMC) through the notch, and does not provide any information about the interface fracture toughness. The vertical part of the curve shows that the notch has been broken down, and the interface has been reached. Afterwards, the crack advanced along the interface. This constant force during crack propagation represents the critical force required to propagate the crack. Its constant value suggests that the critical ERR using 4PB fracture test does not depend on the crack …show more content…
The three methods include VCCT (the main focus), VCE, and the J-integral. A major issue in fracture mechanics simulations is the large degree of freedom of the FE model. It is well known that a three dimensional FE model becomes very computationally expensive to implement, even with the minimal number of elements across the thicknesses, which in turn causes a very large aspect ratio in the simulation model. This chapter presents an effort to develop a simpler, low-cost two dimensional model to evaluate the system. With the test conformation, the problem can be assumed to be plane strain. The very good agreement between FE analysis results and the analytical solution confirmed this assumption (discussed in section 5.4, Fig.
Fig. 5.3 shows a typical load-displacement curve of the 4PB fracture test. The slope of the linear part of the curve corresponds to the stiffness of the whole structure. The peak force represents the required force for fracture of the upper layer (EMC) through the notch, and does not provide any information about the interface fracture toughness. The vertical part of the curve shows that the notch has been broken down, and the interface has been reached. Afterwards, the crack advanced along the interface. This constant force during crack propagation represents the critical force required to propagate the crack. Its constant value suggests that the critical ERR using 4PB fracture test does not depend on the crack …show more content…
The three methods include VCCT (the main focus), VCE, and the J-integral. A major issue in fracture mechanics simulations is the large degree of freedom of the FE model. It is well known that a three dimensional FE model becomes very computationally expensive to implement, even with the minimal number of elements across the thicknesses, which in turn causes a very large aspect ratio in the simulation model. This chapter presents an effort to develop a simpler, low-cost two dimensional model to evaluate the system. With the test conformation, the problem can be assumed to be plane strain. The very good agreement between FE analysis results and the analytical solution confirmed this assumption (discussed in section 5.4, Fig.