Weili Cheng

Measurement of Residual Hoop Stresses in Cylinders Using the Compliance Method

A method is proposed for measurement of the hoop stress in an axisymmetric residual stress field in cylinders in which the axial stress is independent of the axial coordinate. The method involves measuring strains at the outside surface while an axial crack is cut progressively from the outside. Experimental results are presented for two short cylindrical rings cut from a long quenched cylinder. Good general agreement is obtained with X-ray and hole drilling measurements of residual stresses.

KII solutions for an edge-cracked strip

Abstract Mode II stress intensity factors for very shallow and very deep edge cracks in a strip are discussed. Based on the treatment of the two limiting cases, an expression is proposed for any ratio of crack size to strip width. Very good agreement with results available in the literature is obtained. The solution for the displacement due to mode II loading is also presented.

Measurement of residual stress distributions near the toe of an attachment welded on a plate using the crack compliance method

Abstract Using solutions based on fracture mechanics, the authors have developed a technique referred to as the “crack-compliance method” to measure residual stresses. In the present paper the method is applied to the measurement of residual stresses either at the toe of a weld joining a bracket to a plate or at the toe of a fillet weld between two plates. It is shown that the crack compliance functions for a wide range of configurations may be obtained by combining the solutions for an edged-cracked plate with a simple finite element computation. Experimental results are presented for a specimen which simulates the attachment of a bracket to the wall of a nuclear reactor pressure vessel.

Deformation of an edge-cracked strip subjected to normal surface traction on the crack faces

Abstract New solutions for stresses due to a pair of horizontal or vertical forces acting symmetrically on the surface of a strip are obtained and shown to be easier to evaluate than those that are available in the literature. The displacements and strains on the surface due to a normal stress distribution on the faces of a crack in the strip are then obtained by using Castiglianos theorem. It is shown that the displacement at a distance larger than the thickness of the strip from the crack is essentially a rigid body movement. The solutions obtained provide a basis for residual stress measurement from measurement of displacements or strains.

Deformation of an edge-cracked strip subjected to an arbitrary shear surface traction on the crack faces

Abstract The displacements and strains due to a shear surface traction acting on the faces of an edge crack in a strip are obtained by using Castiglianos theorem. It is shown that the displacement at a distance larger than the thickness of the strip from the crack becomes essentially a rigid body movement. The solutions obtained provide a basis for measurement of residual shear stress from observations of displacements or strains.

A mechanism for sub-surface median crack initiation in glass during indenting and scribing

The initiation of sub-surface median cracks in glass during indenting and scribing is studied. It is shown that the zone of intense deformation under the tool introduces a weak singularity which may have a strong influence on crack initiation. When combined with a crack nucleus, which need only be of the order of the dimensions of the glass network, the weak singularity allows the threshold load for median cracking to be estimated. This estimate is shown to be in good agreement with experimental observations. The analysis explains the sudden transition from brittle to ductile behaviour in glass and also provides a possible explanation for the origin of the elusive “Griffith flaws”.

Determination of Stress Intensity Factors for Partial Penetration Axial Cracks in Thin-Walled Cylinders

An approach based on the use of rotation and displacement solutions for a cracked element in plane strain is used to obtain the stress intensity factor for a long axial crack in a thin-walled cylinder. The hoop stress distribution in the cylinder prior to introduction of the crack is arbitrary. Results obtained with this approach are in good agreement with numerical solutions for several hoop stress distributions.

A Summary of Past Contributions on Residual Stresses

In past one and half decades we have presented our work in 24 specialized papers for a variety of configurations of residual stress measurements. A technique, often referred to as the crack compliance method, was first developed using the solutions of linear fracture mechanics, which uses a thin cut of increasing depth to release residual stress incrementally on the plane of measurement. Later developments have greatly expanded its application to near surface measurement and through-thickness measurement in many complex geometries. Another technique, which we refer to as the single slice method, is recently developed for measurement of the residual axial stress in plane strain. An important feature of the technique is that it allows the original stresses to be measured from a fractured part. This summary will cover the basic concepts and applications of the techniques.

Analysis of the fluid-elastic vibration of a U-bend tube bundle induced by cross-flow in PWR steam generators

Cross-flow-induced vibration in a U-bend tube bundle causes wear and fretting fatigue in PWR steam generators and has received considerable attention in the past decade. However, all the previous studies were based on the equation of motion for straight tubes. In this paper the equations of motion for U-bend tubes subjected to cross-flow are derived. Analytical solutions for responses to fluid dynamic forces are then obtained.

Computation of stress intensity factors for a 2-D body from displacements at an arbitrary location

An approach to stress intensity factor computation is presented which allows accurate estimation using a simple finite element program and a coarse mesh of elements. The stress intensity factor is obtained from what we term the Crack-Displacement (C-D) Factor. This involves the rate of change of displacements with crack length at the same location remote from the crack due to two loading conditions. One loading condition is merely that applied to the cracked body. The other loading condition is a virtual line force applied at the location at which the displacement rates are computed. The accuracy of the procedure is demonstrated for uniform tensile stresses applied to a center-cracked panel and an edge-cracked strip.