scholarly journals Evaluation of SSY boundary using DIC results

2021 ◽  
Author(s):  
Antunes FV ◽  
Jose Vasco-Olmo ◽  
Francisco Diaz ◽  
Diogo Neto ◽  
Sérgio ERA ◽  
...  
Keyword(s):  
Aluminium Alloys ◽  
Large Scale ◽  
Pure Titanium ◽  
Image Correlation ◽  
Small Scale ◽  
Commercially Pure Titanium ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement ◽  
Numerical Work ◽  
Scale Yielding

In this work the boundaries of small-scale yielding (SSY) and large-scale yielding (LSY) have been experimentally evaluated from the analysis of crack tip opening displacement (CTOD) measured by Digital Image Correlation (DIC). The approach published in a previous numerical work [18] has been used to define the boundaries of SSY and LSY. According to this approach, CTOD must be resolved into its elastic and plastic components, analysing the ratio between the elastic CTOD range and the total CTOD range ( Δδ/ Δδ) to define the boundary where SSY conditions can be established. Three materials have been studied, commercially pure titanium and 2024-T3 and 7050-T6 aluminium alloys, tested at different stress ratio values (0.1 and 0.6 for titanium, and 0.1, 0.3 and 0.5 for the aluminium alloys). SSY conditions are shown to dominate when Δδ/ Δδ≥79% and ≥78% for titanium and the two aluminium alloys, respectively. In addition, LSY can be established when Δδ/ Δδ≤66.3% and ≤67.2% for titanium and for 2024-T3 and 7050-T6 aluminum alloys, respectively. Transition or LSY conditions are more probable in fatigue tests conducted at low R-ratio than in tests at high R-ratio. In addition, crack lengths above 40% with respect to the width of the specimen promote transition or LSY conditions. The results obtained in this work can assist to a better understanding of the mechanisms driving fatigue crack growth.

Plastic relaxation at a crack tip by asymmetric slip

1988 ◽  
Vol 418 (1854) ◽  
pp. 261-280 ◽  
Keyword(s):  
Slip Band ◽  
Crack Opening ◽  
Crack Tip ◽  
Friction Stress ◽  
Small Scale ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement ◽  
Sharp Crack ◽  
Scale Yielding ◽  
Crack Tip Opening

Relaxation at a sharp crack tip by a single slip band is considered. It is shown that for mixed-mode loading of a plane crack in an isotropic medium there is a unique angle between the slip band and the crack for which the energy release rate (or stress intensity factor) of the crack can be reduced to zero. For such a slip-band calculations are made of the slipband length and the crack-opening displacement as a function of the loading, crack length and friction stress acting on dislocations in the slip band. For small-scale yielding, a simple model is discussed that gives a good approximation to the crack-tip opening displacement and slip-band angle.

Review of Tensile Strain Capacity Prediction Models for Strain-Based Design of Pipelines

2019 ◽  
Author(s):  
Dong-Yeob Park ◽  
James A. Gianetto
Keyword(s):  
Fracture Toughness ◽  
Large Scale ◽  
Prediction Models ◽  
Failure Criteria ◽  
Small Scale ◽  
Aging Effects ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement ◽  
Strain Capacity ◽  
Critical Issues

Abstract In this paper, three tenile strain capacity (TSC) prediction models developed for strain-based design (SBD) of girth-welded pipelines were reviewed, together with a brief introduction of technical backgrounds of their development. Most TSC models rely on small-scale mechanical and fracture toughness measurements to estimate the TSC of pipelines. Hence, we surveyed published experimental and computational data to examine the transferability of small-scale fracture toughness measurements to large-scale pipe fractures. Lastly, some gaps and issues that were found from the review are proposed for improvement of TSC models for SBD. The critical issues found with current TSC models and SBD are (a) differences in strain measurement for full-scale pipe tests/simulations, (b) multiple crack tip opening displacement (CTOD) definitions, (c) no application of J-integral as a toughness parameter, (d) no consensus on failure criteria, and (e) inconsideration of thermal and natural strain aging effects.

A Closure Model to Crack Growth Under Large-Scale Yielding and Through Residual Stress Fields

2003 ◽  
Vol 125 (2) ◽  
pp. 183-190 ◽  
Author(s):  
C. H. Wang ◽  
S. A. Barter ◽  
Q. Liu
Keyword(s):  
Residual Stress ◽  
Crack Growth ◽  
Crack Closure ◽  
Large Scale ◽  
Equivalent Stress ◽  
Future Research ◽  
Closure Model ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement ◽  
Scale Yielding

This paper presents a closure model for predicting the growth behavior of short cracks in the presence of large-scale yielding and residual compressive stresses, representative of structures that have been shot-peened. The plasticity-induced crack closure model developed by Newman is first extended by using the cyclic crack-tip opening displacement as the correlating parameter for fatigue crack growth rates. This new approach also enables a better characterization of the effect of large-scale yielding on short crack growth. The effect of residual stress on crack closure is then analyzed by adding to the loading spectrum an equivalent stress, which varies with the applied load level and the crack size. It is shown that predictions of the extended closure model are within a factor of two of the experimental results of etched specimens tested under spectrum loading, highlighting the capability of the predictive model along with some important issues for future research in this area.

A Fracture Mechanics Based Approach to the Assessment of Seismic Resisting Steel Structures

2006 ◽  
Vol 312 ◽  
pp. 89-94 ◽  
Author(s):  
Clark Hyland ◽  
W. George Ferguson
Keyword(s):  
Stress Intensity ◽  
Fracture Mechanics ◽  
Crack Initiation ◽  
Large Scale ◽  
Crack Tip ◽  
Steel Structures ◽  
Constructional Steel ◽  
Small Scale ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement

A method for assessing likelihood of brittle fracture in cyclically loaded steel assemblies subjected to inelastic strains is proposed. The method proposed is based upon relationships between monotonic and cyclic endurance of steel specimens proposed by Kuwamura and Takagi, and analysis of crack tip opening displacement (CTOD), Charpy V-Notch (CVN) and tensile results of pre-strained, fatigue pre-cracked and side-grooved specimens of constructional steel. The proposed method allows the influence of displacement ductility classification (as used in seismic design of structures), notch geometry, and cyclic strain amplitude history on crack initiation to be incorporated into a single design analysis approach. Small scale CTOD testing of steel materials with various levels of pre-strain may be used to identify stress intensity and crack tip displacement at crack initiation for use in the analysis. The integration of a fracture mechanics based approach to analysing stress intensity in conjunction with assembly plastic deformation characteristics derived from finite element modeling offers the promise of an improved approach to steel assembly design for cyclic plastic endurance and should result in more reliable structures and reduced need for large scale testing. This has particular relevance to the structural design of seismic resisting steelwork assemblies which are expected to develop dependable ductile behaviour under high strain variable amplitude cyclic actions.

Experimental Evaluation of the M-Integral in an Elastic-Plastic Material Containing Multiple Defects

2012 ◽  
Vol 80 (1) ◽  
Author(s):  
N. Y. Yu ◽  
Q. Li ◽  
Y. H. Chen
Keyword(s):  
Path Dependence ◽  
Large Scale ◽  
Plastic Material ◽  
Image Correlation ◽  
Small Scale ◽  
Elastic Plastic ◽  
Multiple Defects ◽  
Scale Yielding ◽  
Elastic Plastic Material ◽  
M Integral

An experimental technique for evaluation of the M-integral in an elastic-plastic material containing multiple defects is proposed by using digital image correlation (DIC). This technique makes direct use of the definition of M by experimentally evaluating the integrand of M at various points along a square contour and determining the integral by numerical integration. The nonlinear Ramberg–Osgood model is used to capture the elastic-plastic behavior such as the elastic-plastic stress and the total strain energy density in terms of the measured displacements by DIC used in an ARAMIS 4M instrument. Compared with the previous experimental method proposed by King and Herrmann (King and Herrmann, 1981, “Nondestructive Evaluation of the J and M Integrals,” ASME J. Appl. Mech., 48, pp. 83–87), the present technique could be suitable to measure the M-integral for the various complicated damages, specimen geometries, loading conditions, and material behaviors. The path-independence or path-dependence of the M-integral is investigated under small-scale and large-scale yielding conditions, respectively. It is found that the values of M are path independent when the contours entirely enclose the nonlinear plastic region near the multiple defects. In contrast, the path-dependence is concluded for an elastic-plastic solid under large-scale yielding condition when the contours have to pass through the plastic zone. This interesting path-dependence of the M-integral is consistent with numerical prediction via the finite element method and theoretical analysis developed in this paper.

Fully Plastic Solutions and Large Scale Yielding Estimates for Plane Stress Crack Problems

1976 ◽  
Vol 98 (4) ◽  
pp. 289-295 ◽  
Author(s):  
C. F. Shih ◽  
J. W. Hutchinson
Keyword(s):  
Plane Stress ◽  
Large Scale ◽  
Crack Opening ◽  
Opening Displacement ◽  
Stress Strain ◽  
Linear Elastic ◽  
Strain Relation ◽  
Stress Strain Relation ◽  
Crack Problems ◽  
Scale Yielding

Fully plastic plane stress solutions are given for a center-cracked strip in tension and an edge-cracked strip in pure bending. In the fully plastic formulation the material is characterized by a pure power hardening stress-strain relation which reduces at one limit to linear elasticity and at the other to rigid/perfect plasticity. Simple formulas are given for estimating the J-integral, the load-point displacement and the crack opening displacement in terms of the applied load for strain hardening materials characterized by the Ramberg-Osgood stress-strain relation in tension. The formulas make use of the linear elastic solution and the fully plastic solution to interpolate over the entire range of small and large scale yielding. The accuracy of the formulas is assessed using finite element calculations for some specific configurations.

Recent Developments in Japanese Flaw Assessment Methods of WES 2805

2008 ◽  
Author(s):  
Yukito Hagihara ◽  
Masayoshi Kurihara ◽  
Hitoshi Yoshinari ◽  
Takashi Miyata
Keyword(s):  
Welded Joints ◽  
Large Scale ◽  
Welded Joint ◽  
Estimation Method ◽  
Assessment Methods ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement ◽  
Design Curve ◽  
Load Carrying ◽  
Recent Developments

The standard for the method of assessment for flaws in the welded joints of WES 2805 was first published in 1976 and was revised in 1980 and 1997. A further revision has been carried out by the technical committee of FTS in the Japan Welding Engineering Society and the revision was completed in 2007. The standard of WES 2805 is based on a CTOD (crack tip opening displacement) design curve approach for brittle fracture, and is used for the assessment of the significance of flaws in a stress concentrated region, where large scale yielding takes place. Main topics for the recent developments for flaw assessment methods are described in this paper. These are the interaction criterion of multiple flaws, fatigue crack growth laws, determination of equivalent crack length and strain due to stress concentration, estimation method of the critical CTOD from Charpy energy and proposal of partial safety factors. In order to examine the effectiveness of the standard, extensive 2-D and 3-D FE analyses are performed for various welded joints such as a load-carrying fillet welded joint, a non-load-carrying fillet welded joint and a box welded joint. Some of them are introduced in this paper. Their analytical results indicate that the present CTOD design curve method gives a reasonable evaluation.

Experimental Study of Crack Propagation at the PCB/Underfill Interface due to Thermal Aging

2020 ◽  
Author(s):  
Pradeep Lall ◽  
Padmanava Choudhury ◽  
Jaimal Williamson
Keyword(s):  
Fracture Toughness ◽  
High Temperature ◽  
Flip Chip ◽  
Operating Time ◽  
Image Correlation ◽  
Beam Specimen ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement ◽  
Substrate Interface ◽  
2D Digital Image Correlation

Abstract Flip-Chip Ball Grid Arrays (FCBGAs) are finding applications in automotive underhood electronics for enablement of safety-critical functions. Underfills needed to reinforce flip-chip interconnects in FCBGAs need to operate reliably under sustained high temperature operation. Underfill-to-substrate interface is one of the primary failure locations under wide thermal excursions and usually a precursor to flip-chip joint failure. In order to assess the reliability in the end application, there is need for understanding the damage progression of the underfill-to-substrate interface as a function of operating time and operating temperature. In this study, the Substrate-UF interface was exposed to high temperature and the interfacial fracture toughness quantified. A three-point composite beam specimen of PCB/Underfill was fabricated to study the interface and thermally aged for periods of 10 days, 30 days, 60 days at temperatures ranging from 100°C to 150°C. Quasi-static bending was used to observe and determine interfacial delamination of the sample specimen. A 2D-Digital Image Correlation (DIC) method was also employed to understand the Crack tip opening displacement (CTOD), crack initiation and the fracture toughness, CTOD were compared with the aging schedule and temperature.

Two Parameter J-A Estimation for Weld Centerline Cracks in Welded Single-Edge Cracked Plate Under Tensile Loading

2019 ◽  
Author(s):  
Chuanjie Duan ◽  
Shuhua Zhang
Keyword(s):  
Large Scale ◽  
Tensile Loading ◽  
Small Scale ◽  
Material Strength ◽  
Single Edge ◽  
Weld Width ◽  
Elastic Plastic ◽  
Cracked Plate ◽  
Scale Yielding ◽  
Two Parameter

Abstract This work examines the J–A two-parameter characterization of elastic–plastic crack front fields for weld centerline cracks under tensile loading. Extensive finite element analyses (FEA) have been conducted to obtain solutions of constraint parameter A, which is the second parameter in a three-term elastic-plastic asymptotic expansion for the stress field near the tip of mode-I crack, for modified boundary layer (MBL) model and welded single-edge cracked plate (SECP). Solutions of the constraint parameter A were obtained for the material following the Ramberg-Osgood power law. The crack geometries analyzed include shallow and deep cracks, and remote tension loading levels cover from small-scale to large-scale yielding conditions. The effects of weld material mismatch and weld width on crack tip constraint were considered in the FEA. A constraint parameter AM, only caused by material strength mismatch, is defined and its parametric equation was obtained. The total constraint in the bi-material weldment can be predicted by adding together AM and A in the homogeneous material. Good agreements were achieved for welded SECP specimen with different crack size and weld width from small-scale to large-scale yielding conditions. This methodology would be useful for performing constraint-based elastic-plastic fracture analyses of other welded test specimens.

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