Fracture Assessment Methods Research Articles

The study on fracture response of cracked pipeline considering the Lüders effect

Since pipeline steel typically exhibits yield discontinuities, some pipelines may experience high local strains during service that exceed the strain limits required by existing fracture assessment methods, thereby posing a significant threat to pipeline integrity. By establishing a finite element fracture model of a cracked pipeline with the Lüders effect and incorporating a developed constitutive model with a trilinear stress-strain relationship, the mechanical and fracture responses of the cracked pipeline with the Lüders effect under uniaxial tensile loading are analyzed in this study. The effects of crack configurations and material parameters on the crack driving force are discussed in detail. The results indicate that an increase in crack length and strain hardening exponent lowers the crack driving force plateau and shortens its length. Conversely, increases in crack depth, softening modulus, and Lüders strain raise the crack driving force plateau. Specifically, as crack depth increases, the plateau length of the crack driving force shortens, while an increase in the softening modulus and Lüders strain extends the plateau length. These conclusions provide guidance for the fracture analysis and assessment of pipelines with cracks affected by the Lüders effect.

Chest CT-based automated vertebral fracture assessment using artificial intelligence and morphologic features.

Spinal degeneration and vertebral compression fractures are common among the elderly that adversely affect their mobility, quality of life, lung function, and mortality. Assessment of vertebral fractures in chronic obstructive pulmonary disease (COPD) is important due to the high prevalence of osteoporosis and associated vertebral fractures in COPD. We present new automated methods for (1) segmentation and labelling of individual vertebrae in chest computed tomography (CT) images using deep learning (DL), multi-parametric freeze-and-grow (FG) algorithm, and separation of apparently fused vertebrae using intensity autocorrelation and (2) vertebral deformity fracture detection using computed vertebral height features and parametric computational modelling of an established protocol outlined for trained human experts. A chest CT-based automated method was developed for quantitative deformity fracture assessment following the protocol by Genant etal. The computational method was accomplished in the following steps: (1) computation of a voxel-level vertebral body likelihood map from chest CT using a trained DL network; (2) delineation and labelling of individual vertebrae on the likelihood map using an iterative multi-parametric FG algorithm; (3) separation of apparently fused vertebrae in CT using intensity autocorrelation; (4) computation of vertebral heights using contour analysis on the central anterior-posterior (AP) plane of a vertebral body; (5) assessment of vertebral fracture status using ratio functions of vertebral heights and optimized thresholds. The method was applied to inspiratory or total lung capacity (TLC) chest scans from the multi-site Genetic Epidemiology of COPD (COPDGene) (ClinicalTrials.gov: NCT00608764) study, and the performance was examined (n=3231). One hundred and twenty scans randomly selected from this dataset were partitioned into training (n=80) and validation (n=40) datasets for the DL-based vertebral body classifier. Also, generalizability of the method to low dose CT imaging (n=236) was evaluated. The vertebral segmentation module achieved a Dice score of.984 as compared to manual outlining results as reference (n=100); the segmentation performance was consistent across images with the minimum and maximum of Dice scores among images being.980 and.989, respectively. The vertebral labelling module achieved 100% accuracy (n=100). For low dose CT, the segmentation module produced image-level minimum and maximum Dice scores of.995 and.999, respectively, as compared to standard dose CT as the reference; vertebral labelling at low dose CT was fully consistent with standard dose CT (n=236). The fracture assessment method achieved overall accuracy, sensitivity, and specificity of 98.3%, 94.8%, and 98.5%, respectively, for 40,050 vertebrae from 3231 COPDGene participants. For generalizability experiments, fracture assessment from low dose CT was consistent with the reference standard dose CT results across all participants. Our CT-based automated method for vertebral fracture assessment is accurate, and it offers a feasible alternative to manual expert reading, especially for large population-based studies, where automation is important for high efficiency. Generalizability of the method to low dose CT imaging further extends the scope of application of the method, particularly since the usage of low dose CT imaging in large population-based studies has increased to reduce cumulative radiation exposure.

Improvement of fracture assessment method for pipe girth weld based on failure assessment diagram

The increasing demand for oil and gas resources in China has promoted the rapid construction and development of oil and gas pipeline networks. With an increase in the mileage of high-grade pipeline, the intrinsic safety of pipeline girth weld faces serious challenges, and the existing fracture assessment methods have many shortcomings. The failure assessment diagram of the commonly used fracture assessment method in engineering is taken as the research object. Aiming at deficiency that it cannot accurately consider the strength matching characteristics of girth welds. Based on the failure assessment diagram theory and the equivalent stress-strain relationship method, the influence of crack size, pipeline diameter-thickness ratio, and material parameters on the fracture assessment accuracy of the girth weld is studied. The calculation method of optimized limit load and reference stress is established. Moreover, the improved fracture assessment process of pipeline girth weld is proposed, which makes up for the lack of conservative assessment results in traditional methods and improves the accuracy of fracture assessment girth weld under high-stress conditions.

Effects of material properties and mismatch on unified constraint parameter

In order to develop unified constraint-based fracture assessment method, it needs to investigate the effects of material properties and mismatches on the unified constraint parameter and develop the parameter solutions for cracked structures. In this work, the effects of material properties (yield strength and hardening exponent) and strength mismatch on the in-plane and out-of-plane unified constraint parameter Ad* of semi-elliptical surface cracks in homogeneous and welded plates have been investigated. The results show that the parameter Ad* does not essentially change with yield strength and hardening exponent of materials for cracks in homogeneous plates under bending and tension loads. The parameter Ad* of weld centerline cracks in welded plates under bending and tension loads is essentially independent on the strength mismatch. These advantages of Ad* are conducive to the development of its solutions for homogeneous and welded structures containing cracks. The effect of weld width on Ad* is related to loading mode, mismatch (undermatch or overmatch) and crack size. The mechanism of the influence of material properties, strength mismatch and weld width on Ad* has been explained by its definition and the crack-tip plastic strain distribution. The development and application of Ad* solutions for homogeneous and welded structures also have been discussed.

Fracture toughness assessment of axial partially through cracks in X65 and X70 steel pipes

This paper presents analysis of fracture assessment methods of axial partially-through crack in X65 and X70 steel pipes with internal pressure. Two analytical methods Folin–Ciocalteu method (FC method) and Gauss–Seidel method (GS method)) are used to make assessment for two steel pipes (steel X65 and X70). Finite Element model of X65 and X70 steel full-scale pipes with axial part-through crack was established. In this work, a comparison is made between results obtained from FC and GS methods and finite element model with previous experimental results. The GS is more conservative assessment method as it provides smaller crack depth (a) corresponding to (Jcr). Finite Element model in case of steel X70 is more conservative than the analytical methods and its results close to the experimental values.

Fracture Risks Related to Parity and Breastfeeding Effect in Post-Menopausal Women Aged Sixty and Over: Results from the “Quality of Bone in Lorraine” Register

Introduction: The long term effect of accumulation of genital events as repeated pregnancy and longer breastfeeding in bone heath later in women’s life is still disputed. The objective was to assess the impact of parity and cumulated duration of breastfeeding on fracture risk in post-menopausal women aged sixty an over. Patients and Methods: It was a leading study from the register “Quality of Bone in Lorraine (QBL)” achieved in the department of endocrinology and osteoporotic disease of Nancy (France). This register included all patients sent for an assessment of the bone mass density from January 1, 2006 to December 31, 2014 (9 years). It was about post-menopausal women aged sixty an over suffering or not from osteoporosis fracture or bone fragility just after the age of 45. The genital events of patients to their age (from puberty to menopause) as well as the existence of hormone replacement therapy use, parity, and breastfeeding duration were taken into account. The assessment of bone fracture was clinical, radiological or by using the vertebral fracture assessment method. Results: 861 post-menopausal women were included. In comparison to the control group, the fractured population had a mean age of (74.3 ± 9 vs. 72 ± 8 years), a family history of fracture (32.1% vs. 26%), and an average input of calcium (2.4 ± 1 vs. 2.3 ± 0 portions per day). The age at menarche was of 12.8 ± 1 years in each group, a mean genital activity duration of (36.8 ± 3 vs. 37.2 ± 3 years), a parity of (2.1 ± 1 vs. 1.8 ± 1 children), a cumulated breastfeeding duration (4.2 ± 16 vs. 3.1 ± 5 months) and an age of menopause of (48.6 ± 4 vs. 48.6 ± 4 years) were respectively found in fractured and witness population. Overall, an osteoporotic fracture has been rediscovered in 50.9%. In multivariate analysis, only a cumulative duration of breastfeeding of 6 months and over was associated with a higher fracture risk (OR = 1.5 [1.1 - 2.2]). The impact of parity was not significant (OR = 1.1 [0.7 - 1.8]). Association with obesity was quasi significant (OR = 1.3 [0.9 - 1.9]). There was no correlation between the fracture risk and the genital activity duration (OR = 0.7 [0.5 - 1.0]), hormone replacement therapy use (OR = 1.0 [0.8 - 1.4]), daily calcium input (OR = 0.8 [0.6 - 1.3]), and age of menarche (OR = 1.0 [0.9 - 1.1]). Conclusion: This work confirms a negative impact from 6 months of cumulative breastfeeding. The modest effects observed may be related to the selection of Caucasian patients who live in an economically developed country with a limited number of pregnancies and limited duration of breastfeeding.

A new acute scaphoid fracture assessment method: a reliability study of the \u2018long axis\u2019 measurement

BackgroundThe aim of this study was to assess the inter observer and intra observer reliability of acute scaphoid fracture classification methods including a novel ‘long axis’ measurement, a simple method which we have developed with the aim of improving agreement when describing acute fractures.MethodsWe identified sixty patients with acute scaphoid fractures at two centres who had been investigated with both plain radiographs and a CT (Computed Tomography) scan within 4 weeks of injury. The fractures were assessed by three observers at each centre using three commonly used classification systems and the ‘long axis’ method.ResultsInter observer reliability: based on X-rays the ‘long axis’ measurement demonstrated substantial agreement (Intraclass Correlation Coefficient (ICC) =0.76) and was significantly more reliable than the Mayo (p < 0.01), the most reliable of the established classification systems with moderate levels of agreement (kappa = 0.56). Intra observer reliability: the long axis measurement demonstrated almost perfect agreement whether based on X-ray (ICC = 0.905) or CT (ICC = 0.900).ConclusionsThis study describes a novel pragmatic ‘long axis’ method for the assessment of acute scaphoid fractures which demonstrates substantial inter and intra observer reliability. The ‘long axis’ measurement has clear potential benefits over traditional classification systems which should be explored in future clinical research.

A modified fracture assessment method for pipelines under combined inner pressure and large-scale axial plastic strain

Owing to ground movement, in-service pipelines may be subjected to large scale axial plastic strain. Therefore, determining the fracture capacity of pipelines with crack-like defects is a key issue that needs to be addressed. In this study, to conduct an engineering critical assessment (ECA) for in-service pipelines, the limit load solution of Kastner for pipelines with circumferential surface cracks under tension was modified based on the von Mises yield criterion. Then, the limit load solution of Kastner was adapted to the situation under combined inner pressure and axial plastic strain. Furthermore, the optimised reference stress method was applied to improve the accuracy of the ECA for in-service pipelines. Finally, the formula for the non-dimensional parameter, γ, was developed.

WES 2808 for Brittle Fracture Assessment of Steel Components under Seismic Conditions – Part VI: Application of WES 2808 to Beam-to-column Connections

This paper describes application of revised fracture assessment method specified in WES 2808 to full-scale models of beam-to-column connections subjected to cyclic and dynamic loading. Fracture tests of full-scale models of beam-to-column connections were carried out (Morita, 1999, and Yoshimura, 2006). Cyclic loading tests were conducted, which included dynamic loading tests. Brittle fracture occurred from weld defects (lack of fusion or weld crack) or artificial defects in beam-to-column connections. In accordance with WES 2808, the fracture strain at the beam end in the connection was evaluated. Fracture toughness of a local area including fracture initiation site was replaced by the static fracture toughness at reference temperature defined by WES 2808. The equivalent CTOD ratio β was employed to correct the constraint loss in structural components on the basis of the Weibull stress criterion. The fracture performance of full-scale models of beam-to-column connections evaluated by the procedure specified in WES 2808 was almost consistent with the experimental results.

Engineering fracture assessment of FV520B steel impeller subjected to dynamic loading

The dynamic fracture assessment method applied to a cracked centrifugal impeller subjected to dynamic loading is the focus of this study. J-integral histories and loading rates at crack tips were evaluated by numerical simulation through ABAQUS and Zencrack software. True stress–strain relations, fracture mechanism and fracture toughness of the impeller material FV520B steel were investigated over a wide range of loading rates by experimental and theoretical methods. Fracture assessment with consideration to rate effects was then conducted based on the CEGB R6 procedure. The present method demonstrated advantages over existing methods evaluated by an equivalent static load.

Fracture behavior evaluations for ferritic steel piping with circumferential double flaws on the inner surface

Methods for assessing the structural integrity of nuclear components having some flaws are provided in the Rules on Fitness-for-Service for Nuclear Power Plants of the JSME code (JSME FFS code). Although the JSME FFS code provides such methods for piping with a single flaw, it does not describe any method for fracture assessment of piping with multiple flaws including flaw coalescence criteria. Some investigations on the fracture behavior of mainly austenitic stainless steel piping with multiple flaws, whose fracture mode is plastic collapse, have recently been reported and fracture assessment methods have been proposed. In the present study, fracture tests and analyses of carbon steel piping with a single and two circumferential flaw(s) on the inner surface were conducted to investigate a method for fracture assessment of ferritic steel piping with multiple flaws. It was found that fracture assessment based on the twice elastic slope method and the plastic collapse mechanism gave inadequate results for a large single flaw. Including this case, two kinds of elastic–plastic fracture assessment method, one using the Z-factor in the JSME FFS code and the other by ductile instability analysis, gave conservative estimates of fracture strength even when the structural factor SF was not considered (i.e. SF = 1).

Vertebral Compression Fractures: Towards a Standard Scoring Methodology in Paleopathology

AbstractVertebral compression fractures are the most common osteoporotic fractures in postmenopausal women. Notwithstanding, its clinical diagnosis remains ambiguous. In paleopathological studies, vertebral fractures and/or deformations are frequently disregarded. When observed, vertebral compression fractures are usually recorded without the support of quantifiable and comparable protocols. As such, Genant's semi‐quantitative method for vertebral compression fracture assessment was applied to a large sample (N = 196) from the Coimbra Identified Skeletal Collection, Portugal, and the reliability of the method was tested. Vertebral fracture scoring agreement was evaluated with the kappa statistic and the per cent of agreement. Intra‐observer agreement was almost perfect, whereas inter‐observer agreement was substantial to almost perfect. The Genant's semi‐quantitative scoring methodology is easy to apply and highly reproducible; as such, it should be adopted as the standard method to score vertebral fractures in any paleopathological investigation. Copyright © 2014 John Wiley &amp; Sons, Ltd.

Reconsideration of the relevance of mild wedge or short vertebral height deformities across a broad age distribution.

Based on an evaluation of vertebral fracture prevalence on lateral radiographs across all age groups in a large cohort, mild or wedge-shaped vertebral body changes identified among adults should be managed as osteoporosis or at least considered as a risk factor for osteoporotic fracture, since they are rare among young subjects. Radiographic assessment of vertebral fractures is limited by the inability to distinguish mild fractures from congenital mild wedge deformities or vertebrae of short vertebral height. We attempted to quantify the expected background prevalence of these deformities by measuring vertebral fracture prevalence across all age groups in a large hospital-based retrospective Chinese cohort. We reviewed eligible lateral chest radiographs from patients admitted to Peking Union Medical College Hospital during 2011 using the Genant semiquantitative method for vertebral fracture assessment (T4-L2). We evaluated fracture prevalence among subjects by sex, 10-year age group, and fracture severity grades subjectively. We further analyzed characteristics of subjects with mild (grade I) fractures to estimate the relative contribution of congenital mild wedge deformities. A total of 10,720 subjects (5,396 men and 5,324 women) with lateral chest radiographs were evaluated. Subjects ranged in age from 0.5 to 97 years with a mean of 51.8 ± 17.4 years (men 52.8 ± 17.6 years; women 50.8 ± 17.2 years). When stratified by 10-year age groups, the prevalence of vertebral fractures was relatively low until about 40 years of age, after which prevalence increased for both genders. Fractures (13 fractures for 9 males and 6 fractures for 5 females) seen in subjects younger than 40 years of age were almost exclusively mild grade fractures. No fractures were identified in subjects younger than 20 years of age. Mild or wedge-shaped vertebral body changes on lateral radiographs are rare among young subjects, indicating that when mild vertebral deformities are found among adults, they are likely to be the product of aging and not congenital variation. Clinically, therefore, mild vertebral body changes should be managed as osteoporosis or at least considered as a risk factor for osteoporotic fracture.

Vertebral fractures and self-perceived health in elderly women and men in a population-based cross-sectional study: the Tromsø Study 2007–08

BackgroundHealth-related quality of life (HRQL) may be associated with increased mortality in the elderly. The effect of prevalent vertebral fractures on HRQL in elderly women and men is not well described. The purpose of this study was to examine the association between prevalent vertebral fractures and back pain, neck pain, and HRQL in elderly women and men, and to study possible gender differences in the reported pain and HRQL.MethodsInformation on prevalent vertebral fractures was ascertained by a vertebral fracture assessment (VFA) method (dual-energy X-ray absorptiometry (DXA), GE Lunar Prodigy) in 2887 women and men, mean age 65.4 (SD 9.4) who participated in the population-based Tromsø Study which was conducted in 2007–08. Bone mineral density (BMD; g/cm2) was measured by DXA at the femoral sites. Self-reported HRQL was assessed using the standardized measures EQ-5D-3 L and EQ VAS from the EuroQol Group. Lifestyle information was collected by questionnaires. The association between vertebral fractures and pain was analyzed using logistic regression, between vertebral fractures and EQ-5D-3 L and EQ VAS scores by multiple regression analyses.ResultsIn women, presence of vertebral fractures was associated with an increased risk of back pain with an OR of 1.76 (95% CI: 1.24 – 2.50) after adjustments for age, height, weight, and BMD. Women with vertebral fractures had lower EQ-5D-3 L scores (p < 0.001) than women without vertebral fractures, also after adjustments. These associations were not present in men. Type of fracture was not associated with EQ-5D-3 L scores, but increasing numbers (p < 0.001) and severity of fractures (p < 0.002) were associated with decreasing EQ-5D-3 L score in women.ConclusionPrevalent vertebral fractures are associated with increased risk of back pain and reduced HRQL in postmenopausal women, but not in men.

Equivalent CTOD Concept for Correction of CTOD Toughness for Constraint Loss in Steel Weld Components

This paper presents a new fracture assessment method, IST method developed as ISO 27306. The IST method implements an equivalent CTOD ratio, β, for the CTOD toughness correction for constraint loss in structural components. Using β, the standard fracture toughness specimen and structural components are linked at the same level of the Weibull stress. This paper extends the equivalent CTOD concept to weld components. Effects of the weld strength mismatch and residual stress on β are discussed. It is shown on the failure assessment diagram (FAD) that the CTOD toughness correction with β leads to accurate fracture assessments of weld panels, whereas the conventional procedure gives much conservative results.

Fracture assessment for a dissimilar metal weld of low alloy steel and Ni-base alloy

Recently, instances of SCC in Ni-base alloy weld metal of light water reactor components have been reported. Despite the possibility of propagation of SCC crack to the fusion line between low alloy steel (LAS) of pressure vessel and Ni-base alloy of internal structure, a fracture assessment method of dissimilar metal welded joint has not been established. The objective of this study is to investigate a fracture mode of dissimilar metal weld of LAS and Ni-base alloy for development of a fracture assessment method for dissimilar metal weld. Fracture tests were conducted using two types of dissimilar metal weld test plates with semi-elliptical surface crack. In one of the test plates, the fusion line lies around the surface points of the surface crack and the crack tips at the surface points have intruded into LAS. Material ahead of the crack tip at the deepest point is Ni-base alloy. In the other, the fusion line lies around the deepest point of the surface crack and the crack tip at the deepest point has intruded into LAS. Material ahead of the crack tip at the deepest point is LAS. The results of fracture tests using the former type of test plate reveal that the collapse load considering the proportion of ligament area of each material gives a good estimation for fracture load. That is, fracture assessment based on plastic collapse mode is applicable to the former type of test plate. It is also understood that a fracture assessment method based on the elastic-plastic fracture mode is suitable for the latter type of test plate.

Fracture assessment method for steel structures under seismic conditions: idea of fracture assessment and assessment flow

Fracture assessment method for steel structures under seismic conditions: idea of fracture assessment and assessment flow

高強度鋼における延性き裂の進展とその後の脆性破壊限界条件に関する検討

Fracture behavior showing ductile-to-brittle transition in steel is quite important for the assessment of structures against catastrophic failure. Recently various fracture assessment methods have been established. In such methods, all toughness data of target steel including ductile-to-brittle behavior must be collected before evaluation. Also consideration about ductile crack is not sufficient. This report picks up high strength steel and designs to clarify ductile-to-brittle behavior from standpoint of mechanics in two stages: i,e, 1)ductile crack initiation and extension 2)subsequent brittle fracture . Consequently it became clear that both of two stages could be evaluated by criteria obtained from simple small testing. This can indicate suggestions for more detailed fracture assessment in various structures and more rational material designing.

ワイブル応力を用いた破壊評価手法 - Part I

ワイブル応力を用いた破壊評価手法 - Part I

Application of ductile fracture assessment methods for the assessment of pressure vessels from high strength steels (HSS)

The economical and safe design of pressure vessels requires, besides others, also a detailed knowledge of the vessel failure behaviour in the case of existing imperfections or cracks. The behaviour of a cracked component under a given loading situation depends on material toughness. For ferritic steels, the material toughness is varying with temperature. At low temperature dominantly brittle fracture behaviour is observed, at high temperature the failure mode is dominantly ductile fracture. The transition between these two extremes is floating. In the case of existing or postulated cracks, the safety analysis has to be performed using fracture mechanics methods. In the lower shelf of toughness, K Ic as of ASTM E 399 is the characterising value for crack initiation and immediate unstable crack extension (cleavage). In the upper shelf level the characterising value is the ‘actual crack initiation toughness’ J i acc. to ISO 12135, characterising the onset of slow stable crack extension. For the transition regime in ASTM E 1921 the instability values K Jc are defined, characterising cleavage failure after more or less extended ductile crack growth. The safety analysis of a component operated in the upper shelf of the material toughness, has to consider initiation as well as stable crack extension following initiation. The inclusion of any crack extension into this consideration needs to consider the influence of the constraint in front of a crack tip, leading to multiaxial stress conditions and decreasing the material crack resistance significantly. Thus, the exclusion of crack initiation needs to be proven in a first step of each safety analysis. Assessing the component in a uniform way over the relevant temperature range is possible by using initiation characteristics, which also have the advantage of transferability. A change of criterion considering initiation at the lower shelf, instability in the transition range and again initiation in the upper shelf can be avoided. Depending on the aim of the analysis, the fracture mechanics safety analysis procedures can be used to determine the critical load, the critical crack size or the required material characteristic.