Determination of KIC fracture toughness by crack initiation of a compact tension steel specimen

Lim , Eng Har (2008) Determination of KIC fracture toughness by crack initiation of a compact tension steel specimen. Masters thesis, Universiti Malaysia Sabah.

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Abstract

Fracture toughness parameter has been a critical concept in Fracture Mechanics (FM) analysis. In theory, the toughness parameter can generally be defined as the energy release rate, G, and the stress intensity factor, K. The latter fracture toughness parameter approach is applied in this research in which the plane-strain fracture toughness, KIc, of a medium Carbon-steel is determined as to characterize the applicability of Linear Elastic Fracture Mechanics (LEFM) concepts. The experimental implementation of the KIc fracture toughness evaluation is through the crack initiation approach by Crack Opening Displacement (COD) of highly constrained Compact Tension (CT) geometry-fabricated specimens, based on the ASTM Standard Test Method for Plane Strain Fracture Toughness of Metallic Materials, coded E-399, using the Instron Universal Testing Machine. Such geometry has been designed to constrain crack-tip sharpness and minimize negligible local crack-tip plastic zone for LEFM-concepts to be applicable, which is verified via the crack initiation zone measurement and the cleavage trademarks (river pattern and feather mark) identification using the Infinite Focus Microscope (IFM) and the Scanning Electron Microscope (SEM) alongside with the COD toughness characterization. In addition, a numerical analysis is carried out to provide comparative study to the experimental results using ANSYS version 9.0. This research found that the analyzed medium Carbon-steel with 0.33%C, 43% pearlite structure, hardness 183HB and Yield strength 360.40MPa achieves the plane-strain fracture toughness of 33MPa.m½ 1 beyond a critical thickness of 22mm. Through the microscopic works, the bandwidth of crack initiation zone has been identified at 10µm and the fracture surfaces within the zone possess cleavage microstructure deformation. This has further proven the applicability of LEFM-concepts can be achieved through the determination of KIc fracture toughness, the measurement of crack initiation zone and the identification of cleavage trademarks at the zone.

Item Type:Thesis (Masters)
Uncontrolled Keywords:fracture toughness parameter, energy release rate, stress intensity factor, Linear Elastic Fracture Mechanics (LEFM) concept, crack initiation, compact tension, identification of cleavage trademark, steel specimen
Subjects:T Technology > TA Engineering (General). Civil engineering (General)
Divisions:SCHOOL > School of Engineering and Information Technology
ID Code:6427
Deposited By:IR Admin
Deposited On:27 Jun 2013 11:54
Last Modified:27 Jun 2013 11:54

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