### Abstract

In this study the reliability of yield strength (YS) and total elongation (TE) of friction stir process (FSP) 7075-T6 Al alloy were studied Three different rotation speeds in the FSP were applied namely 1230 1450 and 1670 rpm Transverse tensile test (TTT) and longitudinal tensile test (LTT) were performed both YS and TE used as a raw data for reliability analysis using Weibull statistics Tensile test result revealed both YS and TE have a tendency to decrease with increasing rotation speed The cause of this event is simply due to voids inside the SZ area In order to verify the establishment of void scaning electron microscope (SEM) was used The result showed that the size of the voids increases from 2 4?m to 9 2?m respectively from low to high rotation speed Using Weibull the three-parameter Weibull of YS and TE were analyzed From low to high rotation speed YS (TTT) failure rate found that at low rotation speed such as 1230 rpm the typical graph was increasing failure rate however at 1450 and 1670 rpm the typical graph were decreasing failure rate YS (TTT) reliability found that both m and x_o value affect the graph alteration and lead to 1230 rpm provide better performance than other rotation speed TE (TTT) failure rate found that for TE value <19% 1230 rpm have lower failure rate value than 1450 rpm However if TE value > 19% or about 22% the 1450 rpm lower failure rate values than 1230 rpm TE (TTT) reliability found that m value affect the graph alteration At this parameter we also found that at 1450 and 1230 rpm the graph line is overlap at 22% elongation which lead the reliabity into two section of TE value such as TE <22% and TE > 22% For TE value <22% low rotation speed such as 1230 rpm has better reliability However for TE >22% rotation speed such as 1450 provide better reliability YS (LTT) failure rate found that all rotation speed had the same tendency that is increasing failure YS (LTT) reliability found that both m and x_o value affect the graph alteration and lead to 1230 rpm perform better than other rotation speed in terms of reliability TE (LTT) failure rate found that all rotation speed had the same tendency that is increasing failure rate TE (LTT) reliability found that m value affect the graph alteration that lead to low rotation speed such as 1230 rpm give a better value of reliabilty that other rotation speed The data showed that through the Weibull statistical analysis a failure model in this research revealed low rotation speed like 1230 rpm is reliable enough for further engineering applicationDate of Award | 2014 Aug 13 |
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Original language | English |

Supervisor | Truan-Sheng Lui (Supervisor) |