Strip yield modelling of fatigue crack under variable amplitude loading

The results from 'strip yield' approach of the FASTRAN type models of plasticity induced crack closure effects of fatigue cracks subjected to variable amplitude loadings are presented. The strip yield results are compared with authors' finite element (FE) and experimental results. It has been observed that the strip yield model is seen to be fundamentally limited by choice of alpha (constraint factor) and corresponding to treat baseline closure effects. Double overload closure behavior is functionally similar for both strip yield and FE models. Under multiple overloads, an important functional difference is seen between FE and strip yield models. This has been linked to the absence of in-plane constraint in the strip yield model, which is seen to have a distinct decreasing influence on on-going closure effects.Peer reviewedFinal Accepted Versio

Modelling of combined roughness and plasticity induced closure effects in high strength Al-alloys

An investigation of plasticity induced crack closure (PICC) and roughness induced crack closure (RIC C) behaviour using finite element (FE) methods is presented for cracks subjected to small scale yielding (SSY) conditions. For constant amplitude (CA) undeflected cracks have been examined under both plane strain and plane stress conditions, whilst plane strain analyses have been particularly considered for deflected cracks. A previous two dimensional analytical treatment of RICC (2D CA RICC) [Parry, 2000] has been extended to produce a 'continuous' closure model matching the FE findings. The model is further modified to address three dimensional effects and compared to detailed experimental findings. Results shows the increase in closure levels with increasing twist angle (rjJ) are less significant compared to that with increasing tilt angle (8). Further FE modelling of PICC and RICC for cracks subjected to single overloads is presented. A single overload analytical model of PICC proposed by Parry has been modified following similar arguments to the CA-RICC model. The analytical model has further been modified to address RICC effects during single overloads. Effects of Llrp ratios on deflected cracks during overloads are seen to be functionally similar to RICC under constant amplitude loading (particularly in the 'saturation' of RICC influence for Llrp(OL) &gt; 1), where L, rp and rp(OL) are deflected crack length, baseline plastic zone size and overload plastic zone size respectively. Competitive influences of PICC and RICC effects during single overloads are identified in both the FE and simplified analytical models. A modified 'strip yield' analytical model of the 'FASTRAN'-type [Xu, 2001] has also been used to study PICe effects during single overloads. Comparisons of models and experimental closure and growth rate studies are presented. Investigations have then been extended to consider both double and multiple overload conditions. In particular, attempts are made to study the effects of overload spacing on closure levels and growth rates. It appears to exist a maximum overload interaction zone for double overloads which severity of overload closure effect is at its greatest. Overall it is found that key functional aspects of the various FE models are reproducible in simple analytical representations of RICC and PICC efforts. Whilst some fitting is involved, good correlation of the present analytical models and experimental data is shown, opening a potential route to improve, computationally efficient, multimechanistic fatigue lifing methods involving crack closure.</p

Modelling of combined roughness and plasticity induced closure effects in high strength Al-alloys

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Finite Element modelling of &apos;Rang Ghar&apos; monument, Assam

Abstract: This paper presents the results of static and dynamic analyses of the masonry monumental structure &apos;Rang Ghar&apos; constructed during the Ahom dynasty (1744-1751 AD) in Sibsagar district of Assam, India, using the commercial finite element (FE) software, Abaqus (2010). Rang Ghar is a two storied masonry monumental structure of 12 meter height, with a dome type roof, thick masonry walls and a series of arch openings at both floors. The static analysis shows that, in general, the structural configuration of the masonry complex is adequate to withstand gravity loads (self weight and live load). Most stressed region is the entrance arch walls at the ground level with a maximum value of compressive stress of about 0.45 MPa. Also, displacement resultant distribution suggests that a maximum displacement of around 0.94 mm at top arch roof. Based on the dynamic analysis, first three mode shapes of the Rang Ghar have been presented

Stress intensity factors based fracture criteria for kinking and branching of interface crack: application to dams

In this paper, the application of contour integral method (J. Elast. 8 (1978) 21; On the marriage of fracture mechanics and mixed finite elements methods: an applications to concrete dams, Ph.D. Thesis, University of Colorado, 1993) for determination of bimaterial stress intensity factors in the case of crack lying between rock/concrete interface of gravity dam is shown using the concepts of linear elastic fracture mechanics. The kinking angle of the interface crack is computed based on the maximum circumferential stress criteria. Criteria for branching are proposed [Appendix]

Some issues on finite element modelling of plasticity induced crack closure due to constant amplitude loading

An investigation of plasticity induced crack closure (PICC) behaviour using finite element (FE) method is presented for cracks subjected to constant amplitude loading and small scale yielding (SSY) conditions. Undeflected cracks have been examined under both plane strain and plane stress conditions. Anomalous near-tip closure in FE models has been identified to occur under both plane stress and plane strain conditions and is seen to vary with baseline load levels and crack propagation algorithms. In the case of plane strain models, propagation algorithms are seen to influence pre-crack closure. In general terms it may be said that none of the plane strain models showed crack closure that could be related to ongoing/steady-state crack growth: crack closure in all cases was dominated by pre-crack contact, and/or anomalous near-tip contact, even for the relatively long crack propagation used in the low loading range models

Roughness- and plasticity-induced fatigue crack closure under single overloads: analytical modelling

A simple micromechanical model for the competitive influences of roughness-induced crack closure (RICC) and plasticity-induced crack closure (PICC) on fatigue during single peak overloads has been developed following the approach of Kamp et al. [Kamp N, Parry MR, Singh KD, Sinclair I. Acta Mater 2004;52:343]. This is seen to be functionally comparable to the finite element results of the accompanying paper [Singh KD, Khor KH, Sinclair I. Acta Mater 2006;54:4393], and consistent with a range of experimental data. Competitive influences of PICC and RICC effects during overload transients are particularly identified here

Roughness-and plasticity-induced fatigue crack closure under single overloads: finite element modelling

Results from finite element modelling of plasticity-induced crack closure (PICC) and roughness-induced crack closure (RICC) of fatigue cracks subjected to single overloads are presented. Effects of L/r(p) ratios on RICC, where L and r(p) represent crack asperity length and plastic zone size, respectively, are seen to be functionally similar to results presented previously for constant amplitude fatigue loading [Kamp N.. Parry MR, Singh KD, Sinclair I. Acta Mater 2004;52:343-53], particularly in the saturation of the influence of RICC for L/r(p(OL)) &gt;= I, where r(p(OL)) is the overload plastic zone size. The present work is seen to map out overload regimes where RICC and PICC effects may be expected to influence crack growth transients. Comparisons of modelled and experimental closure levels, and growth rate studies are presented, with the accompanying paper [Singh KD, Khor KH, Sinclair I. Acta Mater (in press)] considering a simplified analytical representation of the effects presented here