A generic approach for a linear elastic fracture mechanics analysis of components containing residual stress

Lee, Hyeong Y.,Nikbin, Kamran M.,O'Dowd, Noel P. Elsevier 2005 The International journal of pressure vessels and Vol.82 No.10

<P><B>Abstract</B></P><P>A review of through thickness transverse residual stress distribution measurements in a number of components, manufactured from a range of steels, has been carried out. Residual stresses introduced by welding and mechanical deformation have been considered. The geometries consisted of welded T-plate joints, pipe butt joints, tube-on-plate joints, tubular Y-joints and tubular T-joints as well as cold bent tubes and repair welds. In addition, the collected data cover a range of engineering steels including ferritic, austenitic, C–Mn and Cr–Mo steels. The methods used to measure the residual stresses also varied. These included neutron diffraction, X-ray diffraction and deep hole drilling techniques. Measured residual stress data, normalised by their respective yield stress have shown an inverse linear correlation versus the normalised depth of the region containing the residual stress (up to 0.5 of the component thickness). A simplified generic residual stress profile based on a linear fit to the data is proposed for the case of a transverse residual tensile stress field. Whereas the profiles in assessment procedures are case specific the proposed linear profile can be varied to produce a combination of membrane and bending stress distributions to give lower or higher levels of conservatism on stress intensity factors, depending on the amount of case specific data available or the degree of safety required.</P>

The influence of nano-silica on the wear and mechanical performance of vinyl-ester/glass fiber nanocomposites

Sokhandani, Navid,Setoodeh, AliReza,Zebarjad, Seyed Mojtaba,Nikbin, Kamran,Wheatley, Greg Techno-Press 2022 Advances in nano research Vol.13 No.1

In the present article, silica nanoparticles (SNPs) were exploited to improve the tribological and mechanical properties of vinyl ester/glass fiber composites. To the best of our knowledge, there hasn't been any prior study on the wear properties of glass fiber reinforced vinyl ester SiO₂ nanocomposites. The wear resistance is a critical concern in many industries which needs to be managed effectively to reduce high costs. To examine the influence of SNPs on the mechanical properties, seven different weight percentages of vinyl ester/nano-silica composites were initially fabricated. Afterward, based on the tensile testing results of the silica nanocomposites, four wt% of SNPs were selected to fabricate a ternary composite composed of vinyl ester/glass fiber/nano-silica using vacuum-assisted resin transfer molding. At the next stage, the tensile, three-point flexural, Charpy impact, and pin-on-disk wear tests were performed on the ternary composites. The fractured surfaces were analyzed by scanning electron microscopy (SEM) images after conducting previous tests. The most important and interesting result of this study was the development of a nanocomposite that exhibited a 52.2% decrease in the mean coefficient of friction (COF) by augmenting the SNPs, which is beneficial for the fabrication/repair of composite/steel energy pipelines as well as hydraulic and pneumatic pipe systems conveying abrasive materials. Moreover, the weight loss due to wearing the ternary composite containing one wt% of SNPs was significantly reduced by 70%. Such enhanced property of the fabricated nanocomposite may also be an important design factor for marine structures, bridges, and transportation of wind turbine blades.

A numerical model to simulate ductile tearing-creep crack growth interaction

Oh, Young-Ryun,Kim, Seung-Jae,Kim, Yun-Jae,Ainsworth, Robert A.,Nikbin, Kamran Elsevier 2019 The International journal of pressure vessels and Vol.175 No.-

<P><B>Abstract</B></P> <P>Ductile tearing and creep crack growth are generally treated independently but there are situations in which they can occur simultaneously. First, creep crack growth calculations in components are often continued to large defect sizes in order to determine when limiting conditions for short-term fracture are reached. Secondly, in order to obtain data in reasonable timescales, experimental creep crack growth tests are often performed at high loads such that plasticity occurs in the tests, particularly as the crack grows to larger sizes. This paper presents a numerical model to simulate the interaction of ductile tearing and creep crack growth to address such cases. A strain-based damage model is introduced with total damage assumed to be the linear summation of creep and plastic damage. The model is applied to Type 316H stainless steel at 550 °C with the parameters in the damage model determined from tensile, creep and fracture toughness test data. Predictions using the proposed model are then compared with notched creep tensile and creep crack growth test results and shown to be in good agreement with experimental measurements of creep deformation and crack growth.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A numerical model to simulate creep crack growth is proposed. </LI> <LI> A strain-based damage model assuming linear summation of creep and plastic damage is introduced. </LI> <LI> Simulated results are compared with notched creep tensile and creep crack growth test results of Type 316H stainless steel at 550 °C </LI> <LI> Comparison of simulated results with experimental data showed good agreement. </LI> </UL> </P>

Comprehensive Residual Stress Distributions in a Range of Plate and Pipe Components

Hyeong-Yeon Lee,Jong-Bum Kim,Jae-Han Lee,Kamran M. Nikbin 대한기계학회 2006 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.20 No.3

A comprehensive review of through thickness transverse residual stress distributions in a range of as-welded and mechanically bent components made up of a range of steels has been carried out, and simplified generic transverse residual stress profiles for a plate and pipe components have been proposed. The geometries consisted of welded pipe butt joints, T-plate joints, tubular T-joints, tubular Y-joints and a pipe on plate joints as well as cold bent tubes and pipes. The collected data covered a range of engineering steels including ferritic, austenitic, C-Mn and Cr-Mo steels. Measured residual stress data, normalised with respect to the parent material yield stress, has shown a good linear correlation versus the normalised depth of the region containing the residual stress resulting from the welding or cold-bending process. The proposed simplified generic residual stress profiles based on the mean statistical linear fit of all the data provides a reasonably conservative prediction of the stress intensity factors, Whereas the profiles for the assessment procedures are fixed and case specific, the simple bilinear profiles for the residual stresses obtained by shifting the mean and bending stress form the mean regression line have been proposed and validated.

Comprehensive Residual Stress Distributions in a Range of Plate and Pipe Components

Lee Hyeong-Yeon,Kim Jong-Bum,Lee Jae-Han,Nikbin Kamran M. The Korean Society of Mechanical Engineers 2006 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.20 No.3

A comprehensive review of through thickness transverse residual stress distributions in a range of as-welded and mechanically bent components made up of a range of steels has been carried out, and simplified generic transverse residual stress profiles for a plate and pipe components have been proposed. The geometries consisted of welded pipe butt joints, T-plate joints, tubular T-joints, tubular Y-joints and a pipe on plate joints as well as cold bent tubes and pipes. The collected data covered a range of engineering steels including ferritic, austenitic, C-Mn and Cr-Mo steels. Measured residual stress data, normalised with respect to the parent material yield stress, has shown a good linear correlation versus the normalised depth of the region containing the residual stress resulting from the welding or cold-bending process. The proposed simplified generic residual stress profiles based on the mean statistical linear fit of all the data provides a reasonably conservative prediction of the stress intensity factors. Whereas the profiles for the assessment procedures are fixed and case specific, the simple bilinear profiles for the residual stresses obtained by shifting the mean and bending stress from the mean regression line have been proposed and validated.

Treatment of residual stress in failure assessment procedure

Lee, Hyeong-Yeon,Biglari, Farid R.,Wimpory, Robert,Nikbin, Kamran M. Pergamon Press 2006 Engineering fracture mechanics Vol.73 No.13

<P><B>Abstract</B></P><P>The effect of residual stress on component failure has been investigated using the distributions from current failure assessment procedures, and a residual stress profile simple to apply with less conservatism has been proposed for the weld geometries of T-plate and tubular T-joint. The stress intensity factors (SIFs) in the two weld geometries under various types of loads have been calculated using the Green’s function method. The Green’s functions were determined not only for the T-plate but also for the tubular T-joint with the built-in ends. The use of a linear (bending) stress profile, derived from an analysis of measured residual stress distributions in T-plate and tubular T-joints, has been examined. The profile was validated with experimentally measured residual stress distributions in two materials, a high strength and medium strength ferritic steel and two geometries, a T-plate joint and a tubular T-joint for crack lengths up to half the plate or pipe thickness. Whereas the recommended residual stress distributions are geometry and material specific, it is shown that a simplified linear bending profile provides a possible guideline, applicable to a range of materials and geometries, where detailed information on weld procedures or residual stress profiles are unavailable.</P>

The relationship between <i>C_t</i> and contour integrals under small-scale transient creep

Oh, Chang-Sik,Kim, Yun-Jae,Yoon, Kee-Bong,Ainsworth, Robert A.,Nikbin, Kamran Elsevier 2010 Engineering fracture mechanics Vol.77 No.3

<P><B>Abstract</B></P><P>In this paper, the relationship between the <I>C<SUB>t</SUB></I> and contour integrals for small-scale transient creep conditions is established, via elastic-creep finite element analysis. It is found that the <I>C<SUB>t</SUB></I> integral is similar to the contour integral value evaluated roughly at the creep zone size defined as the boundaries where time-dependent effective creep strains equal the instantaneous effective elastic strains and measured normal to the crack plane at the crack tip.</P>

분기관 용접부의 크리프 특성 불균일이 응력 재분배에 미치는 영향

이국희(Kuk-Hee Lee),김윤재(Yun-Jae Kim),윤기봉(Kee-Bong Yoo),Kamran Nikbin,Dave Dean 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.11

This paper attempts to quantify the effect of mismatch in creep properties on steady-state stress distributions for a welded branch vessel. A particular geometry for the branch vessel is chosen. The vessel is modeled by only two materials, the base and weld metal. Idealized power law creep laws with the same creep exponents are assumed for base and weld metals. A mismatch factor is introduced, as a function of the creep constant and exponent. Steady-state stress distributions within the weld metal, resulting from threedimensional, elastic-creep finite element (FE) analyses, are then characterized by the mismatch factor. We can find that average stresses in the weld can be characterized by the mis-match factor. And there is an analogy between elastic-creep and elastic-perfectly plastic.

크리프 불균일 지수를 이용한 분기관 용접부의 크리프 수명 평가법 제시 및 검증

한재준(Jae-Jun Han),김상현(Sang-Hyun Kim),정진택(Jin-Taek Chung),김윤재(Yun-Jae Kim),Kamran Nikbin,David Dean 대한기계학회 2013 대한기계학회 춘추학술대회 Vol.2013 No.3