Fracture mechanics in design and service: ‘living with defects’ - Assessment of defects: the c.o.d. approach

1981 ◽  
Vol 299 (1446) ◽  
pp. 155-167 ◽  
Keyword(s):  
Fracture Toughness ◽  
Fracture Mechanics ◽  
Crack Opening ◽  
Local Stress ◽  
Concentration Effects ◽  
Opening Displacement ◽  
Widespread Application ◽  
Linear Elastic ◽  
Applied Loading ◽  
Displacement Approach

In welded construction particular problems arise with the application of fracture mechanics for the assessment of the effect of defects on structural performance. In many practical cases the use of plane strain linear elastic fracture mechanics methods is invalidated by the actual material thicknesses of interest, by residual stresses or by local stress concentration effects, and by local yielding. The crack opening displacement approach was originally devised as a means of extending linear elastic methods to more widespread application to welded structures. This required the development of a means of assessing fracture toughness, and a means of relating this fracture toughness to the applied loading conditions, and to sizes and types of defects which might be present. The success of this method of assessing defects over a period of some 10-12 years will be illustrated, together with a discussion of the inherent limitations of the approach and possible improvements resulting from recent research into slow tearing and design curve relationships.

The crack opening displacement approach to fracture mechanics in yielding materials

1966 ◽  
Vol 1 (2) ◽  
pp. 145-153 ◽  
Author(s):  
F. M. Burdekin ◽  
D. E. W. Stone
Keyword(s):  
Fracture Mechanics ◽  
Crack Opening Displacement ◽  
Crack Opening ◽  
Opening Displacement ◽  
Critical Crack ◽  
Absolute Size ◽  
Linear Elastic ◽  
Elastic Fracture ◽  
Critical Crack Opening ◽  
Displacement Approach

An introduction is given to the fracture mechanics approach employing the concept of crack opening displacement for application to situations in which linear elastic fracture mechanics is invalidated by yielding. The hypothesis of a critical crack opening displacement to fracture has been examined experimentally using mild steel specimens of vastly differing dimensions. Subsidiary experiments have been carried out to define the factors responsible for the apparent effect of absolute size on the results. A theoretical analysis simulates elastic-plastic conditions to give a relationship between applied stresses and strains, crack length, and crack opening displacement.

Linear translaminar fracture characterization of additive manufactured continuous carbon fiber reinforced thermoplastic

2021 ◽  
pp. 089270572110214
Author(s):  
Weiller M Lamin ◽  
Flávio LS Bussamra ◽  
Rafael TL Ferreira ◽  
Rita CM Sales ◽  
José E Baldo
Keyword(s):  
Fracture Toughness ◽  
Carbon Fiber ◽  
Fracture Mechanics ◽  
Image Correlation ◽  
Fiber Reinforced ◽  
Fused Filament Fabrication ◽  
Critical Energy Release Rate ◽  
Linear Elastic ◽  
Continuous Carbon Fiber ◽  
Carbon Fiber Reinforced

This work presents the experimental determination of fracture mechanics parameters of composite specimens manufactured by fused filament fabrication (FFF) with continuous carbon fiber reinforced thermoplastic filaments, based on Linear Elastic Fracture Mechanics (LEFM). The critical mode I translaminar fracture toughness (KIc) and the critical energy release rate (GIc) are found for unidirectional and cross-ply laminates. The specimens were submitted to quasi-static tensile testing. Digital Image Correlation (DIC) is used to find the stress field. The stress fields around the crack tip are compared to linear elastic finite element simulations. The results demonstrate the magnitude of fracture toughness is in the same range as for polymers and some metals, depending on lay-up configuration. Besides, fractographic analyses show some typical features as river lines, fiber impression, fiber pulls-out and porosity aspects.

The Fracture Toughness of Hardened Tool Steels

1987 ◽  
Vol 109 (4) ◽  
pp. 314-318 ◽  
Author(s):  
D. F. Watt ◽  
Pamela Nadin ◽  
S. B. Biner
Keyword(s):  
Fracture Toughness ◽  
Crack Growth ◽  
Slow Crack Growth ◽  
Crack Opening ◽  
Compact Tension ◽  
Testing Procedure ◽  
Tool Steels ◽  
Opening Displacement ◽  
Tempering Temperature ◽  
Toughness Testing

This report details the development of a three-stage fracture toughness testing procedure used to study the effect of tempering temperature on toughness in 01 tool steel. Modified compact tension specimens were used in which the fatigue precracking stage in the ASTM E-399 Procedure was replaced by stable precracking, followed by a slow crack growth. The specimen geometry has been designed to provide a region where slow crack growth can be achieved in brittle materials. Three parameters, load, crack opening displacement, and time have been monitored during the testing procedure and a combination of heat tinting and a compliance equation have been used to identify the position of the crack front. Significant KIC results have been obtained using a modified ASTM fracture toughness equation. An inverse relationship between KIC and hardness has been measured.

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.

Influence of Sulfur Content on the Fracture Toughness Properties of 2 1/4 Percent Cr-1 Percent Mo Steel

1976 ◽  
Vol 98 (2) ◽  
pp. 135-142 ◽  
Author(s):  
J. F. Copeland
Keyword(s):  
Fracture Toughness ◽  
Sulfur Content ◽  
Detrimental Effect ◽  
Crack Opening ◽  
Analytical Techniques ◽  
Compact Tension ◽  
Compact Tension Specimen ◽  
Tension Specimen ◽  
Microvoid Coalescence ◽  
Opening Displacement

The effects of sulfur content on the fracture toughness properties of 2 1/4Cr-1 Mo steel were evaluated at test temperatures above, at, and below the nil ductility transition temperature (NDTT) of −23°C (−10°F). Small, 12.7-mm (0.5-in.) thick compact tension specimen results were combined with J-integral, Equivalent Energy, and Crack Opening Displacement analytical techniques to provide KIc results up to 22°C (72°F). It was found that the sulfur content of this steel has a large detrimental effect on KIc at the NDTT and above, where microvoid coalescence is the fracture mode. Sulfur has no significant effect at −73°C (−100°F) where cleavage occurs. These results also indicate that the higher Charpy V-notch energy at NDTT, shown by lower sulfur steels, is translatable into increased fracture resistance.

Validation of Linear Elastic Fracture Mechanics in Predicting the Fracture Toughness of Polyethylene Pipe Materials

2015 ◽  
Author(s):  
Tarek M. A. A. El-Bagory ◽  
Hossam E. M. Sallam ◽  
Maher Y. A. Younan
Keyword(s):  
Fracture Toughness ◽  
Fracture Mechanics ◽  
Linear Elastic Fracture Mechanics ◽  
Operating Conditions ◽  
Specimen Thickness ◽  
Crosshead Speed ◽  
Linear Elastic ◽  
Piping Systems ◽  
Elastic Fracture ◽  
Point Bend

The main purpose of the present paper is to compare between the fracture toughness based on linear elastic fracture mechanics (GIC), and that based on nonlinear fracture mechanics (JIC). The material of the investigated pipe is a high-density polyethylene (HDPE), which is commonly used in natural gas piping systems. The welds at the pipe junction are produced by butt-fusion (BF), welding. Curved three-point bend (CTPB), fracture specimens are used. The crosshead speed ranged from 5 to 500 mm/min and specimen thickness ranged from 9 to 45mm for both welded and unwelded specimens at room temperature Ta, equal 23°C. The study reveals that the crosshead speed has a significant effect on the fracture toughness of both welded and unwelded specimens. The results of GIC for different specimen thickness and crosshead speed found previously by the authors [1] have been compared with JIC under the same operating conditions [2]. The comparison between welded and unwelded specimens revealed that in the welded specimens there is a marginal difference between fracture toughness measured using linear elastic fracture mechanics LEFM and elastic plastic fracture mechanics EPFM, for both crosshead speeds.

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