Engineering procedures for design and integrity assessment of structural components containing crack-like defects are highly dependent on accurate fracture toughness and Fatigue Crack Growth (FCG) experimental data. Considering ductile and high toughness structural materials, crack growing curves (e.g. J-R curves) and FCG data (in terms of da/dN vs. ΔK or ΔJ) assumed paramount relevance. In common, these two types of mechanical properties severely depend on real-time and precise crack size estimations during laboratory testing. Optical measurement, electric potential drop or (most commonly) elastic unloading compliance (C) techniques can be employed. In the latter method, crack size estimation derives from C using a dimensionless parameter (μ) which incorporates specimen’s thickness (B), elasticity (E) and compliance itself. Plane stress and plane strain solutions for μ are available in several standards regarding C(T), SE(B) and M(T) specimens, among others. Current challenges include: i) real specimens are in neither plane stress nor plane strain-modulus vary between E (plane stress) and E/(1−ν2) (plane strain); ii) furthermore, side-grooves affect specimen’s stiffness, leading to an “effective thickness”. Results from Shen et al. and from current authors revealed deviations larger than 10% in crack size estimations following existing practices, especially for shallow cracks and side-grooved samples. In addition, compliance solutions for the emerging SE(T) specimens are not yet standardized. As a step in this direction, this work investigates 3-D and side-groove effects on compliance solutions applicable to C(T), SE(B) and clamped SE(T) specimens. Refined 3-D elastic FE-models provide Load-CMOD evolutions. The analysis matrix includes crack depths between a/W = 0.1 and a/W = 0.7 on 1/2T, 1T and 2T geometries. The 1T geometry is taken as the reference and presents width to thickness ratio W/B = 2. Side-grooves of 5%, 10% and 20% are considered. The results include compliance solutions incorporating 3D and side-groove effects to provide accurate crack size estimation during laboratory fracture and FCG testing. The proposals were verified against current standardized solutions and deviations were strongly reduced.

Experimental evaluation of geometry-dependent material’s fracture resistance using constraint-designed SE(T) specimens has proved to be an accurate option to assess the structural integrity of pipelines and pressure vessels reducing excessive conservatism. In this context, this work presents procedures for experimental J-integral and CTOD (δ) evaluation using the eta (η) method applied to tension clamped SE(T) specimens made of homogeneous materials and also containing mismatched joints. Initially, the conceptual background is presented, followed by the description of the refined non-linear finite element models developed, which provide the necessary evolution of load with increased load-line displacement and crack mouth opening displacement. As results, are presented a variety of η factors for J -integral and CTOD calculations, which are not available in current standardized procedures. The main objective is to allow fracture resistance experimental evaluation using specimens of different a/W-ratios, material flow properties, weld joint configurations and levels of weld strength mismatch. The main motivation is the possibility of enhancing accuracy of pressure vessels and piping integrity assessments, since these later present very close fracture conditions if compared to SE(T) specimens. The present results, when taken together with previous developments, extend the knowledge about the use of clamped SE(T) specimens. The reader should enhance the studies about the topic with the complimentary paper with the same title beginning but involving pin-loaded SE(T) specimens.

ResumoEste trabalho apresenta o desenvolvimento de critérios objetivos para a garantia de validade da mecânica da fratura elasto-plástica monoparamétrica, utilizando o parâmetro integral J como descritor dos campos de tensões, deformações e deslocamentos à frente de um defeito do tipo trinca. O mais importante na vertente monoparamétrica da mecânica da fratura é garantir que os campos de tensões no corpo de prova laboratorial sejam comparáveis com os existentes em uma estrutura real para cujo projeto as propriedades retiradas do corpo de prova serão utilizadas (conceito este denominado similitude). Para estabelecer critérios objetivos para a existência de similitude, esse trabalho comparou os campos de tensões obtidos de estruturas de referência sob alta triaxialidade de tensões (MBL) com aqueles obtidos de corpos de provas de mecânica da fratura em escala de laboratório. A matriz de análise permitiu a determinação dos limites de deformação M para geometrias C(T), SE(B) e SE(T) de diversas configurações e para uma faixa de propriedades de material característica de aços estruturais aplicáveis a vasos de pressão e dutos. Os resultados demonstram a baixa restrição à plasticidade de corpos de prova SE(B) e SE(T) com trincas rasas e os efeitos de profundidade de trinca e espessura nos resultados de M. Ainda, alguns comportamentos inesperados foram evidenciados, como no caso em que (para condições particulares de profundidade de trincas) corpos de prova mais finos apresentaram maior restrição a plasticidade do que amostras mais espessas. Sendo assim, o trabalho oferece uma base objetiva para que a similitude seja garantida nas avaliações de integridade estrutural baseadas na mecânica da fratura elasto-plástica suportada pela integral J, seja com seus valores críticos (Jc) ou curvas J-R. Palavras-chave: Limite de deformação; Modelo da camada limite; Integral J; Similitude. DEFORMATION LIMITS (M) FOR THE ONE-PARAMETER ELASTIC-PLASTIC FRACTURE MECHANICS (J INTEGRAL) VALIDITY ON SE(B), C(T) AND CLAMPED SE(T) SPECIMENS AbstractThis work presents the development of objective criteria to ensure the one-parameter elastic-plastic fracture mechanics validity using the J integral to describe the stress/strain/displacement-fields ahead of crack-like defects. The most important aspect of the one-parameter fracture mechanics framework is to ensure that the stress-fields in a reduced laboratory specimen are comparable to those found in real structures (this is the so-called similitude concept). To establish objective criteria for the similitude existence in the analysis, this work compared the stress-fields obtained from high constraint reference models (MBL) with those obtained from laboratory scale fracture mechanics specimens. The analysis matrix allowed the determination of the deformation limits M for C(T), SE(B) and clamped SE(T) geometries considering a wide range of geometrical features and material properties characteristic of structural steels applicable to pressure vessels and pipelines. The results confirmed the low con...

Fracture toughness and Fatigue Crack Growth (FCG) experimental data represent the basis for accurate designs and integrity assessments of components containing crack-like defects. Considering ductile and high toughness structural materials, crack growing curves (e.g. J-R curves) and FCG data (in terms of da/dN vs. ΔK or ΔJ) assumed paramount relevance since characterize, respectively, ductile fracture and cyclic crack growth conditions. In common, these two types of mechanical properties severely depend on real-time and precise crack size estimations during laboratory testing. Optical, electric potential drop or (most commonly) elastic unloading compliance (C) techniques can be employed. In the latter method, crack size estimation derives from C using a dimensionless parameter (μ) which incorporates specimen’s thickness (B), elasticity (E) and compliance itself. Plane stress and plane strain solutions for μ are available in several standards regarding C(T), SE(B) and M(T) specimens, among others. Current challenges include: i) real specimens are in neither plane stress nor plane strain - modulus vary between E (plane stress) and E/(1-ν2) (plane strain), revealing effects of thickness and 3-D configurations; ii) furthermore, side-grooves affect specimen’s stiffness, leading to an “effective thickness”. Previous results from current authors revealed deviations larger than 10% in crack size estimations following existing practices, especially for shallow cracks and side-grooved samples. In addition, compliance solutions for the emerging clamped SE(T) specimens are not yet standardized. As a step in this direction, this work investigates 3-D, thickness and side-groove effects on compliance solutions applicable to C(T), SE(B) and clamped SE(T) specimens. Refined 3-D elastic FE-models provide Load-CMOD evolutions. The analysis matrix includes crack depths between a/W=0.1 and a/W=0.7 and varying thicknesses (W/B = 4, W/B = 2 and W/B = 1). Side-grooves of 5%, 10% and 20% are also considered. The results include compliance solutions incorporating all aforementioned effects to provide accurate crack size estimation during laboratory fracture and FCG testing. All proposals revealed reduced deviations if compared to existing solutions.

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