• Transactions of the Korean Society of Mechanical Engineers
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• v.9 no.1
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• pp.40-46
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• 1985

Some problems such as toughness decrement and stess relief cracking (SRC), many occur when post weld heat treatment (PWHT) is applied to remove residual stress adn hydrogen. In this paper PWHT was carried out under the stress of 0, 98, 196 and 294 MPa (0, 10, 20 and 30kgf/mm$^{2}$ each) to simulate residual stress in HAZ of Cr-Mo steel. The effect of applied stress during PWHT on fracture toughness was evaluated by COD fracture toughness test, micro-hardnes test and observation of SEM. The experimental results are as follows; (1) Fracture toughness of weld HAZ was improved by PWHT, but it decreased as heat treated under the stress. (2)Hardness ratio under the stress of 294MPa (30kg/mm$^{2}$) was lower and fracture toughness was decreased than that of the no stress. (3) Applied stress in weld HAZ during PWHT assisted precipitation of over saturated alloying elements in the structure, so fracture surface at the stress of 294MPa (30kg/mm$_{2}$) appeared the grain boundary failure possibly one of the reasons for PWHT embrittlenment.

• Journal of the Korean Society of Safety
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• v.12 no.4
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• pp.230-240
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• 1997

An experimental research investigation of the fracture properties of polypropylene fiber reinforced concrete is reported. Fibers used in this experiment were two types, monofilament and fibrillated polypropylene fibers. Fiber length was 19 mm, and volume fractions were 0, 1, 2, and 3%. Also, as initial notch depths influence the fracture properties of fiber reinforced concrete, the notch depth ratios by specimen height were 0.15, 0.30 and 0.45. The main objective of this experimental program is to obtain the load-deflection and the load-CMOD curves, to investigate the fracture properties of the polypropylene fiber reinforced concretes. Therefore, the flexural specimen testings on the four-point bending were conducted. Then, the load-load point displacement and the load-crack mouth opening displacement curves were measured. The effects of different volume fractions of the monofilament and the fibrillated polypropylene fiber reinforced concrete on the compressive strength, flexural strength and toughness, stress intensity factor, and fracture energy were investigated through the experimental results.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2009.11a
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• pp.417-420
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• 2009

The purpose of the present study is to evaluate high temperature fracture toughness through the experimental and analytical method. The analysis method is proposed to simulate the fracture toughness of high temperatures. Load-COD curves of compact test specimen acquired by finite element method analysis using hypo elastic model are simulated to determine the crack initiation load on high temperatures. The results of experimental work are in accord with analysis in thermal shock test.

• Journal of Welding and Joining
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• v.2 no.2
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• pp.54-61
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• 1984

Construction of welding structure is greatly dependent upon welding heat cycle. Fracture toughness is decreased remarkablely due to coarse grained HAZ and inequal residual stress of three dimensions to originate in welding. Post weld heat treatment(PWHT) is carried out to increase the fracture toughness of HAZ and to remove the residual stress. There occur some problem such as toughness decrement and stress relief cracking(SRC) in the coarse grained HAZ subject to the effect of tempering treatment. Therefore, in this paper, the effect of heat inputs affecting cooling rate and PWHT under the no stress on fracture toughness were evaluated by crack opening displacement (COD), SEM and micro-hardness test. Experimental results are as follows; 1. Fracture toughness of weld HAZ is dependent upon weld heat cycle and it is decreased with increment of heat input, but the degree of improvement of fracture toughness after PWHT was linearly increased with heat input. 2. Hardness of the parent metal is not changed, but the softening of coarse grained HAZ is remarkable due to PWHT. 3. Fracture surface of as-weld show the perfect brittle fracture with the cleavage fracture, but after PWHT they appear the ductile fracture surface with dimple.