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Obtaining Cohesive Zone Model Parameters for Solder Joints with Fatigue Loading History

Mansouri, Mohammad | 2024

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 57470 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Nourani, Amir; Farrahi, Gholamhossein
  7. Abstract:
  8. With the increasing use of electronic components in various dimensions, the reliability of solder joints has been widely considered. Predicting the failure force of these connections in various configurations and under different loads has recently been the subject of scientific articles. The aim of this research is to establish a relationship between the parameters of the cohesive zone model and the damage parameter of joints. Initially, 13 unloaded specimens were pulled by a hydraulic tensile machine at a strain rate of 0.0001/sec to obtain the breaking force. By calculating the solder area, an average breaking stress of 49.8 MPa was obtained. To investigate the effect of fatigue loading on breaking stress, 12 tests were designed, each sample was a semi-Arcan specimen made of Cu-SAC713-Cu solder, subjected to fatigue loading at 500, 1000, and 2000 cycles. Then, they were subjected to monotonic loading at a strain rate of 0.0001/sec until failure occurred. It was found that the higher the stress level in the first loading cycle and the number of fatigue cycles, the more the breaking strength of the joints decreased compared to samples without fatigue loading history. For example, specimens with initial stress levels between 40 and 43 MPa failed at 38 MPa after 2000 cycles, showing a 22.3% decrease compared to specimens without fatigue loading. Also, statistical analysis revealed that at certain low stress levels in the first cycle and with a small number of fatigue cycles, there was no difference in breaking stress between joints with and without fatigue loading history. For example, samples with 500 fatigue cycles in the range of 35 to 40 MPa did not show significant fatigue damage. Furthermore, by selecting a similar criterion as the reduction in Young's modulus, the amount of fatigue damage created in the samples was determined as a function of the breaking stress. After calculating the damage parameter, the breaking stress of the joints was predicted as a function of the damage parameter and using the available data, as a function of the initial stress and fatigue cycle number. The prediction error of the breaking stress for 5 samples that were tested for validation was approximately 11.5%. The cohesive zone model was obtained using data related to the failure of undamaged samples for specimens without fatigue loading history using finite element software. The parameters used were fracture energy, maximum stress or separation strength, and joint stiffness. After obtaining the damage parameter for specimens with fatigue history, the parameters of the CZM were also calculated, all as a function of the damage parameter
  9. Keywords:
  10. Solder Joints ; Fatigue Life ; Continuum Damage Mechanics ; Cohesive Zone Model ; Fracture Prediction ; Shear Fracture Load ; Ductile Damage ; Fracture Load Prediction

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