Date of Award

Spring 1997

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Mechanical & Aerospace Engineering

Program/Concentration

Engineering Mechanics

Committee Director

Ram Prabhakaran

Committee Member

Stephen G. Cupschalk

Committee Member

Keith M. Williamson

Call Number for Print

Special Collections; LD4331.E57 R39

Abstract

Mechanically fastened joints in pultruded composites are necessary for reasons of maintenance, repair, and assembly. Pultruded composites utilize polymers as matrices and therefore are susceptible to time-dependent effects. The positive effects of increasing the clamping force in bolted joints are well known. To maintain a safe operation of the assembly a minimum clamping force must be guaranteed. But since these materials show time-dependent effects, the bolt-preload relaxes over a period of time. The present study is aimed at investigating the bolt preload relaxation. In this study 1/2 in. thick pultruded sheets were first tested under compression in the thickness direction. Then instrumented steel bolts were used singly to apply preloads to composite specimens. Tests were conducted at three torque levels, at both room temperature and high temperatures. In both cases changes in load and specimen strains were monitored as a function of time and used to develop empirical relations. Relationship between bolt preload and the tightening torque was investigated. The torque coefficient 'K' was determined for both lubricated and unlubricated conditions. Finally the effect of repeated torquing on the strength of the composite and the effect of static load on the bolt preload was studied. This study is aimed at supporting the development of design guidelines related to bolted joints in pultruded composites.

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DOI

10.25777/z71k-de15

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