Crack Paths 2012

Effect of Initial Geometric Misalignments of the Circular

Notched Bar Specimen on the Fatigue Crack Growth

Behavior

I. Kim1,Y.J. Zhao2, B.-H. Choi3* and J. M.Lee4

1 School of Mechanical Engineering, Korea University, 1 5-ga Anam-dong, Sungbuk-gu,

Seoul 136-701, Republic of Korea - ikim@korea.ac.kr

2 School of Mechanical Engineering, Korea University, 1 5-ga Anam-dong, Sungbuk-gu,

Seoul 136-701, Republic of Korea - yongjian@korea.ac.kr

3 School of Mechanical Engineering, Korea University, 1 5-ga Anam-dong, Sungbuk-gu,

Seoul 136-701, Republic of Korea - bhchoi@korea.ac.kr

4 School of Mechanical Engineering, Korea University, 1 5-ga Anam-dong, Sungbuk-gu,

Seoul 136-701, Republic of Korea - mlkjp10803@korea.ac.kr

ABSTRACTI.n this study, the effect of various misalignments of the circular notched

bar(CNB) specimens on the fatigue crack propagation behavior of pipe grade

polyethylene is investigated by three dimensional numerical analyses. The effect of the

asymmetric crack growth of the misaligned C N Bspecimens on the lifetime to failure is

also addressed. Combined misalignments (concentric misalignments + angular

misalignments) of the C N Bspecimen are considered using finite element analysis. In

general, as the misalignments increase, the asymmetric crack growth is accelerated so

that the time to reach the critical SIF decreases. Therefore, it can be understood that

the lifetime to failure of C N Bspecimens can vary noticeably once the C N Bspecimen is

misaligned initially. Considering results from this study, the fatigue crack growth

behavior including the estimation of the lifetime of C N Bspecimens should be addressed

by considering the misalignment effects.

I N T R O D U C T I O N

Plastic pipes have become popular in pipe industry due to their distinct characteristics

such as low cost, lightweight, good impact resistance, flexibility, chemical resistance

and so on. However, it is knownthat plastic gas pipes such as polyethylene pipe do not

have enough the crack growth resistance for both of ductile and brittle fracture

compared to metal gas pipe in the past. To solve those critical problems, plastics

industry have dedicated a lot of efforts to improve the crack growth resistance of pipe

grade polyethylene for both of ductile and brittle fracture continuously. As a result, the

PE100/PE125 grade polyethylene gas pipe resin has been developed by several

polyethylene resin manufacturers. However, current test standards to characterize the

crack growth resistance of polyethylene are not adequate due to unique crack growth

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