Session: 15-01-01: ASME International Undergraduate Research and Design Exposition

Paper Number: 99573

99573 - Failure Analysis of a Bench Vise 

In our history as a species, we have learned more about our failures than our successes, as we are able to identify the causes of a failure and seek ways to prevent it. Failure analysis is one of the most important processes in engineering as it contributes to the better design and reliability of many products. The present work shows the failure analysis of a 5-in bench vise following the ASM International recommended methodology for failure analysis. A bench vise is a simple tool, essential in any workshop, used to clamp or hold an object that is to be worked on. It consists of two parallel jaws, one fixed and other movable through a main screw. Its failure can result in several injuries for the operator. The bench vise under investigation failed just 2 weeks from its first use while holding a screw that was being cut; the stem of the movable jaw broke in two pieces. It was found that this type of vise is designed following the GGG-V-410A standard, usually fabricated with cast iron, and that other users have reported similar failures with this vise model. First, a visual examination of the component and fracture zone was performed. The fracture surface was brittle with no evidence of plastic deformation. A misalignment (casting defect) was observed on the fractured stem. Chevron lines were detected at low amplifications using a stereoscope, indicating that the origin of failure was in a corner of the stem near to a transition radius. Microscopic examination of the fracture surface was performed using a Scanning Electron Microscope equipped with Energy-Dispersive X-ray Spectroscopy. Cleavage was observed, confirming a brittle fracture, whereas the local composition suggested a gray cast iron. Brinell hardness tests were carried out based on the ASTM E10 standard, obtaining a hardness of 118.95 ± 6.85 HB. The microstructure of the vise was analyzed near the fracture zone and away from it. Polished samples were observed with an optical microscope. Away from the fracture zone, superimposed graphite flakes with random orientation as specified in ASTM A 247 were observed. Near the fracture zone, different flake graphite shapes were observed: rosette groupings and interdendritic segregation with random orientation. Samples were etched with Nital. Away from the fracture zone a ferritic-pearlitic matrix was observed, common to gray irons like ASTM A48 type 20. Near the fracture zone, a lower level of perlite was found as well as a non-uniform distribution of ferrite-pearlite. In addition, finite element simulations were performed to simulate the operating conditions in which the component failed. The simulations indicated that the applied loads resulted in stresses (56 MPa) much lower than the tensile strength of the material (138 MPa). This implies that improper usage was not the reason for failure. It was concluded that failure originated due to a poor and non-uniform microstructure resulting from casting. It is recommended to have a greater control of casting process parameters such as cooling rate during solidification, casting temperature and chemical composition. Also, a normalizing treatment is recommended between 885-925 °C to obtain a uniform microstructure. Finally, the importance of certifying the quality of the material, as well as listening to user’s feedback is highlighted.

Presenting Author: Luz Paulina Ramirez Parra Monterrey Institute of Technology and Higher Education

Presenting Author Biography: Student of Mechanical Engineering in the Tecnológico de Monterrey campus Estado de México. Member of the Mechanical Engineering Association in the campus.

Authors:

Luz Paulina Ramirez Parra Monterrey Institute of Technology and Higher Education
Mónica Vanessa Sánchez Trejo Monterrey Institute of Technology and Higher Education
Alan Gustavo Ortiz Aguirre Monterrey Institute of Technology and Higher Education
Alberto Córdoba Casas Monterrey Institute of Technology and Higher Education
Santiago Pietra Santa Alcalá Monterrey Institute of Technology and Higher Education