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The treatment of secondary strains within a strain-based failure assessment diagram
Ainsworth, R.A.,Budden, P.J.,Oh, C.Y.,Kim, Y.J. Applied Science Publishers ; Elsevier Science Ltd 2013 The International journal of pressure vessels and Vol.104 No.-
In a companion paper, proposals for the shape of a strain-based failure assessment diagram (FAD) have been made. The developments in that paper and in related works on strain-based fracture assessment have largely been for remotely applied strains, such as those produced by welding. This paper re-writes existing methods for treating secondary stresses within stress-based FADs in the framework of the proposed strain-based FAD. It is shown that residual strains must be included fully in the elastic regime but at large applied strains their contribution to fracture can be relaxed considerably. Practical methods for inclusion of secondary strains within the strain-based FAD are then developed and shown to be conservative relative to some detailed finite element calculations.
An, Joong-Hyok,Kim, Yun-Jae,Budden, Peter J Elsevier 2010 Engineering fracture mechanics Vol.77 No.14
<P><B>Abstract</B></P><P>This paper provides tabulated solutions of elastic stress intensity factors and crack opening displacements for circumferential through-wall cracked elbows under internal pressure and under in-plane bending, based on extensive three-dimensional elastic finite element analyses covering a wide range of crack lengths and elbow/pipe geometries. The effect of crack length and elbow/pipe geometry on the results is discussed, with particular emphasis on the crack closure behaviour under in-plane bending.</P>
Biaxial stress effects on estimating J under combined mechanical and thermal stresses
Oh, C.Y.,Kim, Y.J.,Budden, P.,Ainsworth, R.A. Applied Science Publishers ; Elsevier Science Ltd 2011 The International journal of pressure vessels and Vol.88 No.10
In this paper, the applicability to bi-axial stress states of a simple approximation proposed in our previous work for quantifying the elastic-plastic J under combined primary and secondary stresses is investigated.To produce the bi-axial stress states, circumferential cracked pipes under combined pressure, axial tension (or compression) and thermal stresses are considered. The results suggest that the proposed approximation can be applied to bi-axial stress states, and is slightly more conservative for bi-axial mechanical stresses than for uni-axial ones. The degree of conservatism decreases with increasing strain hardening exponent and with increasing relative magnitude of secondary stress.
Hong, S.P.,Kim, J.H.,Kim, Y.J.,Budden, P.J. Pergamon Press ; Elsevier Science Ltd 2010 Engineering fracture mechanics Vol.77 No.4
This paper quantifies the effect of internal pressure on plastic loads for elbows with circumferential through-wall and constant-depth part-through surface cracks under in-plane bending. Results are based on FE limit analyses using elastic-perfectly plastic materials and the non-linear geometry option. It is found that, for larger values of r/t, the pressure effect on plastic loads is more pronounced and plastic loads for combined loading cases could be much higher than those for pure bending cases. Full FE data of plastic loads are tabulated, and effects of crack geometries on interaction curves are discussed.
이국희(Kuk-Hee Lee),김윤재(Yun-Jae Kim),Peter J Budden,Karman Nikbin 대한기계학회 2009 대한기계학회 춘추학술대회 Vol.2009 No.5
This paper extends the validity of limit load solutions for thin-walled branch junctions, previously proposed by the authors, to thick-walled cases. It is achieved simply by re-normalizing the thin-wall expressions by the limit loads of thick-wall tubes instead of those of thin-wall tubes. Comparison with finite element results shows overall good agreement.
Oh, C.Y.,Nam, H.S.,Kim, Y.J.,Ainsworth, R.A.,Budden, P.J. Pergamon Press ; Elsevier Science Ltd 2014 Engineering fracture mechanics Vol.124 No.-
Objective: This paper provides validation of R6 elastic-plastic J-estimation methods, via elastic-plastic finite element analyses for circumferentially cracked pipes under combined mechanical and thermal loads. Materials method: In the FE analyses, the relative magnitudes of the mechanical and thermal loads, types of thermal loads, the crack sizes and material hardening are systematically varied. Loading sequence effects for the mechanical and thermal loads are also considered. The FE elastic-plastic J values are compared with those derived using R6 elastic-plastic J-estimation methods. Results: It is shown that there are significant load order effects on elastic-plastic J for large secondary stress cases, but these are conservatively estimated using newly proposed methods in R6.
Kim, C.G.,Bae, K.D.,Kim, Y.J.,Oh, Y.J.,Budden, P.J. Pergamon Press 2015 Engineering fracture mechanics Vol.142 No.-
This paper proposes J-integral and crack opening displacement (COD) estimation equations based on the reference stress method for circumferential through-wall cracked elbows under in-plane bending. For best estimates of J and COD, an optimized reference load, used to define the reference stress, is given. The proposed equations are compared with detailed finite element results. They are further validated against eight published full-scale pipe test data. Comparison of crack initiation and maximum loads shows good agreement.