Date of Award

Spring 2001

Document Type


Degree Name

Doctor of Philosophy in Mechanical Engineering - (Ph.D.)


Mechanical Engineering

First Advisor

R. S. Sodhi

Second Advisor

Reggie J. Caudill

Third Advisor

Sanchoy K. Das

Fourth Advisor

E. S. Geskin

Fifth Advisor

Zhiming Ji


Fastening is the process of connecting one or more parts together with the aid of fastening elements. Unfastening, the reverse of fastening, is the process of separating components from each other by removing or detaching fastening elements. So far, the unfastening process is not well understood, and the analysis about it is not very extensive.

However, the need for disassembly is currently increasing. First, parts have to be taken apart for service and repair, and secondly, for the recycling process. Therefore, there is a need to consider unfastening during the design process in order to enable efficient disassemblies.

The purpose of this dissertation is to develop an analytical model, which enables unfastening analysis during the design of new products. Specifically, (i) a standard nomenclature for defining unfastening related parameters and variables is introduced, (ii) the U-Effort model for deriving the unfastening effort for a variety of commonly used fasteners is developed, (iii) the U-Effort model to model unfastening motion and hence estimate disassembly complexity is extended, and (iv) the U-Force model for estimating the required unfastening force in the case of cantilever and cylindrical snap fits is developed.

The U-Effort model is a detailed study about the unfastening effort and the design attributes of commonly used fasteners. There is a difference between unfastening effort and unfastening force. Unfastening effort depends on several influencing factors, whereas the unfastening force is a more direct calculated value. The influencing attributes for the unfastening effort include the geometry and shape of the fastener and the condition at the end-of-life of the product.

In the U-Force model, unfastening considerations are included in the design phase, mainly through the calculation of unfastening forces. The U-Force model is applied to the cantilever and cylindrical snap fit integral attachments.

The U-Effort and the U-Force models can be used by designers to evaluate the unfastening suitability of new and existing product designs. Fastening elements can be selected based on functionality and the least unfastening effort. The developed models can assist industrial companies engaged in demanufacturing plan their recycling and reuse activities.