Search results

1 – 10 of 20
Article
Publication date: 23 August 2013

Keiji Houjou, Koji Takahashi and Kotoji Ando

The purpose of this study was to investigate the effect of overload (bending moment with plastic deformation: Mp) on three point bending specimen at the fatigue limit of…

Abstract

Purpose

The purpose of this study was to investigate the effect of overload (bending moment with plastic deformation: Mp) on three point bending specimen at the fatigue limit of high-tensile-strength steel containing a crack in the stress concentration zone.

Design/methodology/approach

An artificial semi-circular slit was introduced and Mp was applied after which bending fatigue tests were carried out.

Findings

The relationship between the level of Mp and the fatigue limit (σw) was proportional; the fatigue limits of specimens containing 0.2- and 0.3-mm-deep slits are improved by the Mp process as much as twice the original values; the slit size that can be rendered harmless by the Mp process is a=0.05 mm in depth; and all non-propagating cracks appeared around the artificial slit.

Originality/value

Very few studies have been conducted on the fatigue limit of materials containing crack-like surface defects after overload in the stress concentration zone. This study elucidated the effect of Mp on the fatigue limit.

Details

International Journal of Structural Integrity, vol. 4 no. 3
Type: Research Article
ISSN: 1757-9864

Keywords

Article
Publication date: 5 March 2010

M.M.I. Hammouda and I.G. El‐Batanony

The purpose of this paper is to estimate the number of cycles for fatigue crack initiation in notched plates.

1534

Abstract

Purpose

The purpose of this paper is to estimate the number of cycles for fatigue crack initiation in notched plates.

Design/methodology/approach

Previously published experimental results for tests with initially uncracked U‐shaped notches of different sizes and geometries are utilized. The present work defines the fatigue initiation period, Ni, as number of loading cycles required for the formation of a through‐thickness Mode I crack at the notch root macroscopically propagating along the plate width. Thus, backward extrapolation of the observed early decreasing fatigue growth rates of the initiated crack at the notch root on the specimen surface to zero surface crack size enables the estimation of Ni.

Findings

A parameter based on the normal strain range and the maximum normal stress acting at the notch root best fitted Ni.

Research limitations/implications

This paper provides an estimation of Ni in 3 mm thick mild steel plates subjected to constant amplitude uniaxial cyclic stresses. Initiated‐but‐non‐propagating cracks possibly found at the notch surface and at the notch root along the plate width are distinguished.

Originality/value

Based on the present analysis, a threshold stress is devised to represent the minimum stress level required for the appearance of a through‐thickness crack at the notch root running along the specimen width. Notched plates simulate many engineering applications particularly in aerospace industry.

Details

International Journal of Structural Integrity, vol. 1 no. 1
Type: Research Article
ISSN: 1757-9864

Keywords

Article
Publication date: 11 March 2014

Jun Yasuda, Koji Takahashi and Hideki Okada

The purpose of this study is to clarify the influence of stress ratio (R) on the effects of shot peening (SP) on the fatigue limit of high-strength steel containing an artificial…

Abstract

Purpose

The purpose of this study is to clarify the influence of stress ratio (R) on the effects of shot peening (SP) on the fatigue limit of high-strength steel containing an artificial small defect.

Design/methodology/approach

SP was subjected on the specimens with a semi-circular slit with a depth of a=0.1, 0.2 and 0.3 mm. Then, bending fatigue tests were carried out under R=0.4.

Findings

The fatigue limits of specimens with a semi-circular slit were improved by SP under R=0.4. The fatigue limits of the SP specimens with a semi-circular slit under a=0.2 mm fractured outside the slit, and they had considerably high fatigue limits equal to specimens without a slit. Therefore, a semi-circular slit with a depth of under a=0.2 mm could be rendered harmless by SP under R=0.4. Compared to the results of R=0, the increasing ratios of fatigue limits under R=0.4 were lower than those under R=0. However, the size of semi-circular slit that could be rendered harmless by SP was same. In addition, it was found that whether the semi-circular slit is rendered harmless or not is decided by the relationship between the stress intensity factor range of semi-circular cracks and the threshold stress intensity factor regardless of stress ratio.

Practical implications

The proposed method can be applied to mechanical parts used in vehicles, aircraft and trains.

Originality/value

This is the first paper to investigate the fatigue limits after SP in materials containing a surface defect under positive stress ratio. In this study, the authors investigated the influence of stress ratio on the effects of SP on the fatigue limit containing a surface defects.

Details

International Journal of Structural Integrity, vol. 5 no. 1
Type: Research Article
ISSN: 1757-9864

Keywords

Article
Publication date: 16 November 2012

R.A. Cláudio, J.M. Silva and J. Byrne

This paper aims to present a methodology, based on traditional approaches, to predict the fatigue life and non‐propagating cracks of shot peened components and the damaging effect…

Abstract

Purpose

This paper aims to present a methodology, based on traditional approaches, to predict the fatigue life and non‐propagating cracks of shot peened components and the damaging effect of a scratch created over the treated surface.

Design/methodology/approach

The finite element method is used to determine the actual strain at surface and fracture mechanics parameters calculated from cracks at the surface. The model considers residual stress (in order to introduce the effect of shot peening) and the scratch geometry. The total fatigue life is obtained by adding initiation life, to early and long crack propagation life using appropriate criteria.

Findings

Numerical predictions were compared with previous experimental tests, showing that this method is quite reliable for predicting both fatigue life and non‐propagating cracks of shot peened components, including the effect of damage due to a scratch.

Research limitations/implications

The proposed method provides good results and a clear understanding of the fatigue process, however it requires a considerable amount of both material and shot peening parameters.

Practical implications

The methodology presented in this paper allows the determination of fatigue life and the prediction of non‐propagating cracks for components, including the effects of shot peening and scratch damage. These results can be used to quantify the scratch damage limits of components improved by shot peening.

Originality/value

This paper provides a useful tool for prediction of the effects of shot peening and scratch damage on fatigue life, using traditional approaches.

Details

International Journal of Structural Integrity, vol. 3 no. 4
Type: Research Article
ISSN: 1757-9864

Keywords

Article
Publication date: 13 June 2016

Athanasios Bouboulas and Nikolaos Anifantis

– The purpose of this paper is to investigate the effect of crack surfaces contact on the post-buckling behavior of a slender column with a non-propagating crack.

Abstract

Purpose

The purpose of this paper is to investigate the effect of crack surfaces contact on the post-buckling behavior of a slender column with a non-propagating crack.

Design/methodology/approach

In this paper a 3D finite element model has been implemented to study the post-buckling behavior of a slender column with a non-propagating crack. According to this model, the column is discretized into three-dimensional solid elements. Contact conditions are considered between the crack surfaces. The non-linear equations for this model are solved using an incremental-iterative procedure, and the equilibrium path of the cracked column is extracted.

Findings

Load-displacement curves are presented for a cantilever column with a transverse surface crack of either uniform or non-uniform depth across the column cross-section. For both crack shapes, the load-displacement curves are presented for various values of crack depth and position. The results of this study are in good agreement with the results available in the literature. Comparisons with the results of the always-open crack were performed. The post-buckling behavior of a column with a uniform depth crack is more sensitive to variations in crack depth and position than the post-buckling behavior of a column with a non-uniform depth crack.

Originality/value

A 3D finite element approach for the post-buckling behavior of a transversely cracked column including contact between crack surfaces.

Details

International Journal of Structural Integrity, vol. 7 no. 3
Type: Research Article
ISSN: 1757-9864

Keywords

Article
Publication date: 24 May 2013

Keiji Houjou, Koji Takahashi and Kotoji Ando

The purpose of this paper is to investigate the effect of shot peening (SP) on the fatigue limit of high‐tensile‐strength steel containing a crack in the stress concentration zone.

Abstract

Purpose

The purpose of this paper is to investigate the effect of shot peening (SP) on the fatigue limit of high‐tensile‐strength steel containing a crack in the stress concentration zone.

Design/methodology/approach

An artificial semi‐circular slit was introduced into the bottom of notch, and SP was performed. Bending fatigue tests were then carried out.

Findings

First, the fatigue limits of specimens containing a slit of 0.2 or 0.3 mm in depth were improved up to approximately twice their original values. Second, in the case of shot‐peened specimens with a crack of 0.2 mm in depth, the fractures occurred from outside the slit. Moreover, the specimens recovered to fatigue limits up to those of non‐slit specimens. Finally, the effect of stress concentration (Kt=1.9) on the slit size could be rendered harmless by SP was not found in the fatigue test.

Originality/value

There are very few examples of evaluations of the fatigue limit of materials containing crack‐like surface defects after SP has been performed in the stress concentration zone. The study elucidated the effect of SP on the fatigue limit in such materials, compared with that of a smooth zone.

Details

International Journal of Structural Integrity, vol. 4 no. 2
Type: Research Article
ISSN: 1757-9864

Keywords

Article
Publication date: 30 August 2011

Koji Takahashi, Toshihiko Amano, Kotoji Ando and Fumio Takahashi

The paper's aim is to investigate the effects of shot peening (SP) on the bending fatigue limit of high‐strength steel containing an artificial semi‐circular slit.

Abstract

Purpose

The paper's aim is to investigate the effects of shot peening (SP) on the bending fatigue limit of high‐strength steel containing an artificial semi‐circular slit.

Design/methodology/approach

SP and stress SP (SSP) were conducted on the specimens containing an artificial semi‐circular slit with a depth of a=0.1, 0.2 and 0.3 mm. Then, bending fatigue tests were conducted on the specimens.

Findings

The fatigue limit was improved by SP and SSP. In the case of SP and SSP specimens, the specimens with a semi‐circular slit under a=0.2 mm fractured outside the slit, and they had considerably high fatigue limits. Therefore, a semi‐circular slit with a depth of under a=0.2 mm could be rendered harmless by SP or SSP. It was found that the fatigue limit of specimens with a semi‐circular slit that received SP or SSP was determined by the threshold condition for non‐propagation of fatigue cracks that emanated from outside the slit. Whether the semi‐circular slit is rendered harmless or not is decided by the relationship between the stress intensity factor range of semi‐circular cracks and the threshold stress intensity factor range.

Practical implications

The proposed method can be applied to mechanical parts used in vehicles, aircraft and trains.

Originality/value

There are very few examples of evaluations of fatigue limits after SP in materials containing crack‐like surface defects. This study calcifies the effect of SP on the fatigue limit having crack‐like surface defects.

Details

International Journal of Structural Integrity, vol. 2 no. 3
Type: Research Article
ISSN: 1757-9864

Keywords

Article
Publication date: 14 October 2019

Jakub Šedek, Roman Růžek and Vladislav Oliva

The purpose of this paper is to deal with the FE analysis of strain constraint around the crack tip under cyclic loading and its utilization using crack growth prediction strip…

Abstract

Purpose

The purpose of this paper is to deal with the FE analysis of strain constraint around the crack tip under cyclic loading and its utilization using crack growth prediction strip yield model (SYM). During cycling, the constraint develops based on the load history. The monotonic loading is analyzed mostly, but during cyclic loading the conditions are different. The constraint is analyzed after several loading cycles applied in upwards part of the cycle and the formula for its development is proposed.

Design/methodology/approach

The study is based on the 3D FE analysis of middle-cracked tension specimen M(T). The strain constraint is described by Newman’s factor α. The variability of constraint factor α was analyzed for several load levels and specimen thicknesses. The crack is considered as non-propagating with straight crack front. The material is modelled as elastic-perfectly plastic. The SYM is modified by implementing variable constraint and the experimental results are compared with the simulation.

Findings

In major part of the loading cycle, it was found by FE analysis, that the constraint factor αg is lower after overloads than when creating monotonic plastic deformation on the same load level. The value of αg is governed by the ratio of thickness B over the plastic zone size rp. By implementing the variable constraint factor into the SYM, the improvement of the predicted specimens lives under variable amplitude loading was shown.

Originality/value

The new phenomenon on the variability of strain constraint during cyclic loading is presented. The development of constraint factor αg during cyclic loading is different from the monotonic loading and should be accordingly implemented into prediction models.

Details

International Journal of Structural Integrity, vol. 11 no. 5
Type: Research Article
ISSN: 1757-9864

Keywords

Article
Publication date: 2 March 2012

Keiji Houjou, Koji Takahashi and Kotoji Ando

The purpose of this paper is to describe the effects of stress ratio (R) on the threshold stress intensity factor range (ΔKth) by applied overload and to conduct an analytical…

Abstract

Purpose

The purpose of this paper is to describe the effects of stress ratio (R) on the threshold stress intensity factor range (ΔKth) by applied overload and to conduct an analytical investigation of the effect of the stress ratio.

Design/methodology/approach

Tensile overload was applied to a compact tension specimen, and fatigue tests were performed at R=0.1 or 0.5.

Findings

The value of ΔKth increased as the tensile overload was increased, and the nominal threshold values were given by the equation ΔNKth,R = C+ DKov, where C represents ΔKth, and D is a proportional constant. Experimental results showed that the value of D showed good agreement with theoretical value.

Originality/value

The paper proposes a new model that arrests crack growth or makes cracks harmless by utilizing the overload effect.

Details

International Journal of Structural Integrity, vol. 3 no. 1
Type: Research Article
ISSN: 1757-9864

Keywords

Article
Publication date: 5 February 2018

Ryutaro Fueki and Koji Takahashi

The purpose of this paper is to estimate the acceptable defect size amax after needle peening (NP) and predict the fatigue limit improvement through the use of NP for an…

Abstract

Purpose

The purpose of this paper is to estimate the acceptable defect size amax after needle peening (NP) and predict the fatigue limit improvement through the use of NP for an austenitic stainless steel welded joint containing an artificial semi-circular slit on a weld toe.

Design/methodology/approach

Residual stress and hardness distribution were measured. Microstructures around the weld toe were observed to clarify the cause for the change in hardness after NP. Finite element method analysis was used to analyze the change in the stress concentration following NP. Fracture mechanics was used to evaluate amax after NP. The fatigue limits before and after NP were predicted by determining amax for several levels of stress amplitude.

Findings

The tensile residual stress induced at the surface of the weld toe prior to NP changed to a compressive residual stress after NP. The residual stress near the surface layer after NP exceeded the yield stress prior to NP due to the increase in yield stress as a result of work hardening as well as the generation of a deformation-induced martensitic structure. The stress concentration was reduced due to the shape improvement caused by NP. The estimation value of amax after NP and the prediction results of fatigue limits were in good agreement with the fatigue test results.

Practical implications

The proposed method is useful in improving the reliability of welded joints used in large steel structures, transportation equipments and industrial machines.

Originality/value

From an engineering perspective, it is essential to estimate amax and the fatigue limit of welded joints with crack-like defects. However, it is unclear as to whether it is possible to predict amax and the effects of NP on the fatigue limit for stainless steel welded joints.

Details

International Journal of Structural Integrity, vol. 9 no. 1
Type: Research Article
ISSN: 1757-9864

Keywords

1 – 10 of 20