Development and analysis of Non-Destructive Testing Systems for Fastening Quality of Self-Clinching Fasteners
Date Issued
2009
Date
2009
Author(s)
Lin, Ming-Shian
Abstract
Self-clinching technique utilizes squeezing force to fasten the sheet metal into the special geometric features of tooth structure and undercut of the fastener, enabling thread engagement on the sheet metal as a result of shaped lock and interference fit. Destructive testing systems have been used to detect the destruction on the joints between fasteners and sheet metal during product usage; however, no methods have been developed to examine the defects caused by the fastening process. Therefore, the objective of this research is to develop two different non-destructive testing systems for evaluating the fastening quality of self-clinching fasteners base on aperture size.heoretical calculation, finite element analysis and experimental slices were first performed to analyze the stress-strain pattern. To clearly understand the mechanism of self-clinching fastener joints, the riveting force and features of experimental curves and material deformation were verified. It was found that the larger the aperture in the sheet, the less the metal extrusion into the undercut. This has led to a decreased contact area and pressure between the fastener and the sheet metal. On the other hand, the contact resistance increases as the contact area and pressure decreases. Therefore, finite element analysis was used to establish a set of model to predict the contact resistance whose measurements were conducted using the designed device for fastening quality evaluation. The results showed a positive correlation between the sizes of the aperture and the contact resistance, which indicated the feasibility of the designed method.esides evaluation of static riveting fastening quality, features of fasteners under dynamic loads should also be identified. Both finite element analysis and the designed displacement measuring device were used to examine the dynamic response of the riveted fasteners after controlled mechanical impact. It was confirmed that the sizes of the holes in the sheet metal were positively correlated with half cycles of the dynamic response of the fasteners after the impact, which illustrated the aperture sizes resulted from the fastening process could be detected by the designed method. n sum, this research has demonstrated the feasibility to apply the developed non-destructive testing systems to the evaluation of the fastening quality of self-clinching fasteners. However, others factors affecting the fastening quality should be further examined to strengthen the application of this method, which will contribute to the full inspection of self-clinching qualities in the future.
Subjects
Self-Clinching fastener
non-destructive testing
stress and strain analysis
contact resistance
vibration measurement
Type
thesis
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