DESIGN OF HIGH CYCLE BIAXIAL FATIGUE SAMPLE NEAR RESONANCE USING FINITE ELEMENT MODELING

Open Access
Author:
Sorna, Matthew Anthony
Area of Honors:
Engineering Science
Degree:
Bachelor of Science
Document Type:
Thesis
Thesis Supervisors:
  • Manton Guers, Thesis Supervisor
  • Cliff Lissenden, Honors Advisor
Keywords:
  • fatigue
  • finite element
  • COMSOL
  • natural frequency
  • vibration
  • biaxial
  • high cycle
  • high cycle fatigue
  • MATLAB
  • resonance
Abstract:
Fatigue, the gradual accumulation of damage in of a material due to microstructural damage and subsequent crack growth, is prevalent among almost all components who sustain prolonged periods of cyclic loading. The number of loading cycles until failure is known as the fatigue life of a material, and is a function of the applied cyclic stress history. For certain materials and operating conditions, it is common to assume infinite fatigue life for stress amplitude levels below a certain value, known as the endurance limit. In this work, rectangular fatigue specimens were designed and simulated using finite element analysis software. Both free-free and fixed-free boundary conditions were studied to achieve a near resonance response assuming a commercially available shaker as the source of harmonic excitation. Eigenfrequency studies were used to determine resonant frequencies and time domain studies were used to simulate loading cycle histories. In the time domain analysis, special consideration was required for defining boundary conditions for valid finite element solutions. The results showed that nearly constant stress amplitude cycles were obtainable at the target stress of 140 MPa. By manipulating the free parameters of the shaker, a wide range of relatively low stress amplitudes can be generated to fully explore the high cycle (> 10^8 cycles) fatigue regime. Future work can be done to validate the simulated results, as well as design the appropriate mounting fixtures used to deliver the two boundary conditions used in the simulation. The proposed technique would allow measurement of high cycle fatigue properties, which can inform design choices and reduced costs associated with system failure and costs incurred through system downtime.