bluuebunny/crossref_metadata_2025_split huggingface dataset:
Influence of a zero-load rest period in elevated-temperature fatigue
Authors: Miller K J , Plumbridge W J 
Published: July 2007

A preliminary investigation of the influence of rest periods on Stage I crack growth has been performed on a 2½ per cent Ni Cr Mo steel by testing cylindrical specimens under high-strain reversed torsion conditions at 20, 100, 200, 300 and 400°C. Increases in lifetime of up to 100 per cent are observed, and their magnitude is a function of temperature and the rest-period duration, with maximum lifetime occurring at 300°C and a total rest period of 20 hours. Strain ageing is cited as the dominant process, which explains the dependence of optimum lifetime conditions on both temperature and total rest period duration. Since components are frequently rested and/or subjected to variable strain-rate conditions over a range of temperatures, it is suggested that results obtained from uninterrupted laboratory tests may be conservative unless overageing occurs leading to cyclic softening.
Effects of residual stresses on the ductile strength of plane welded grillages and of ring stiffened cylinders
Authors: Faulkner D 
Published: July 2007

Structural engineers have for a long time accepted the importance of residual stresses when considering fracture modes of failure. It is only in the last quarter-century that attention has been focused on their adverse effect on ductile modes of failure and, in particular, on buckling collapse. The last decade has seen increased research activity, spurred on by recent failures in box-girder bridges. The nature and distributions of locked-in-stresses during hot and cold forming and during welding are outlined. The effect these have on inelastic buckling collapse of flat plated grillages and ring-stiffened cylinders is examined for all likely modes of failure. Experimental data are scarce, but they confirm that both forming and welding stresses can reduce the stiffness and strength of both types of structure very significantly. This is caused by a direct reduction in buckling stresses (as usually supposed), but equally important is the loss in stiffness due to early yield and other effects. In particular the cold-bending of ring-frames can have very serious adverse effects, as shown by recent finite-element programmes. Cold-cambering, and certain other corrective measures adopted by fabricators, seem more likely to weaken the structure than to improve it.
Shrinkage stresses in a thin plate with a central weld
Authors: Kamtekar A G , White J D , Dwight J B 
Published: July 2007

A study was made of the residual stresses caused by weld shrinkage in a plate containing a central longitudinal weld. A theoretical analysis was developed in which the weld was treated as a moving concentrated heat source, through-thickness variations in temperature and stress being ignored. The equations were solved in finite-difference form and the stresses were computed at discrete stages during welding and cooling. Allowance was made for the variation of yield stress with temperature. Computed results were obtained for the bead-on-plate and butt welded cases. Residual stresses were measured in 40 flat plate specimens containing a central butt weld, with thicknesses ranging from 6 to 16 mm. The results led to proposed values for the factors H and C in the simple Moxham formula, which are in reasonable agreement with theoretical predictions.
Allowance for imperfections in ship structural design
Authors: Goodman R A , Mowatt G A 
Published: July 2007

The development of quality standards in shipbuilding is reviewed, and the need for an analytical assessment of standards identified. The use of a probabilistic approach in the form of a reliability analysis is recommended, and a description of a system suitable for this task given. The various levels of complexity which may be involved are described, and the problems of implementation outlined. The method is illustrated by an application of the system developed at Lloyd's Register of Shipping to assess suitable quality standards for initial imperfections in ship plating. To correlate the mathematical simulation of reliability with actual experience, use is made of technical information on structural damages from Lloyd's Register of Shipping Technical Records database.
Radial loading of a cylindrical shell through plate brackets
Authors: Kitching R , Hughes J F , Saedi F 
Published: July 2007

The elastic behaviour of a cylindrical shell subjected to radial load applied through two circumferential plate bracket attachments positioned diametrically opposite each other at the mid length of the cylinder has been investigated experimentally. An existing theoretical analysis, based on the assumption of a uniform distribution of load across a bracket, was modified in the light of the experimental observations which indicated that the assumption was not valid for the size of bracket used. Experimental stress distributions and maximum values of stress in the cylinder are compared with those calculated from the modified analysis in the text, which showed an improvement on the existing analysis for the proportions of the shell and bracket considered.
High-Temperature cumulative damage for stage I crack growth
Authors: Miller K J , Gardiner T 
Published: July 2007

The effects of cyclic shear strain-range, shear strain-rate and temperature on the accumulation of damage during constant and variable shear strain range fatigue tests on a 1 per cent Cr-Mo-V steel are reported. The hypothesis of linear accumulation of damage and the summation of cyclic fractions to unity are shown to be incorrect for interactions of time, cyclic and environmental processes which are considered in detail. Stage I cracks may be accelerated, retarded or stopped and new cracks nucleated. Nevertheless only 8 per cent of the cumulative damage tests in the high strain fatigue regime gave unsafe linear summation factors less than 0.8. None fell below 0.7.
A three-parameter method for determining stress intensity factors from isochromatic fringe loops
Authors: Etheridge J M , Dally J W 
Published: July 2007

Methods for determining the stress intensity factor, K, from isochromatic fringe loops obtained from photoelastic models with sharp cracks are briefly reviewed. A new three-parameter method is introduced which follows the two-parameter approach developed previously by Irwin. In the three-parameter method, three different terms in an analytical solution are adjusted to obtain a suitable match between the theoretical and experimental isochromatic loops. The three parameters are: K/√2πz, which describes the crack-tip singularity, ( b) β K/√z, to account for variations in the stress field removed from the crack tip and ( c) σoa = α1 K/√2πa, which is added to the σ x component of the stres field to account for the biaxiality of the far-field stresses. A relationship is derived for the maximum shear stress, τm, in terms of the three fitting parameters ( K, α, and β) and the two geometric parameters ( rm and θm) associated with the isochromatic fringe loops. A method of solution based on measurements of rm and θm from any two independent fringe loops is given. The accuracy of the three-parameter method was determined by using exact results from the central crack problem for a standard. It was found that the error was within ± 1 per cent for 69° < θm < 145°. Comparison with the two-parameter method shows that the three-parameter method is more accurate and is applicable over a wider range of θm.
The influence of mean stress and thickness on the fatigue crack growth behaviour of the aluminium alloy BS2L71
Authors: Dover W D , Boutle N F 
Published: July 2007

A series of fatigue crack growth tests have been conducted on sheet specimens of thicknesses 3, 6, 16 and 22 mm. These tests have been under both random and constant amplitude loading for a number of different mean stress levels. The results from these tests have shown that the resistance to fatigue crack growth increases as the thickness increases at low growth rates. In contrast, at high growth rates this behaviour is reversed. Both random and constant amplitude data showed this feature. Crack-closure measurements have been used in an attempt to explain these differences in behaviour for high and low growth rates. The random and constant amplitude test results have been correlated successfully for square-mode growth, using a ‘weighted’ average range approach.
On the determination and application of cod to epoxy-bonded aluminium joints
Authors: Chow C L , Woo C W , Sykes J L 
Published: July 2007

A method of analysis is presented for the determination of crack-opening-displacements (COD) and their application to aluminium—Araldite joint systems. Use is made of a beam-on-elastic-foundation (BEF) model, which is extended to represent the physical system. It is seen that, in conjunction with this, the Dugdale ‘strip-yield’ model solution may be combined to characterize interfacial or cohesive fracture cases. Fracture toughness values, based on both load and displacement control testing conditions, are examined and show that the equation derived for the load-control model yields greater accuracy. Results of the proposed method are compared with those obtained by a two-dimensional, finite-element analysis and are found to be in good agreement. The validity of the proposed analysis is further verified by experimental observations employing conventional compliance methods for both interfacial and cohesive fracture modes.
Calculation of stresses in the wall-ironing of cups
Authors: Dood B 
Published: July 2007

The experimentally determined effects of die angle, friction and reduction on the ironing process are briefly described and the limitations of the slab method for the calculation of the ironing load are outlined. Hill's two-centred fan slip-line field for ironing is discussed and the static inadmissibility of some of the solutions is described. A further limitation on these fields is shown to occur when the hydrostatic pressure at the slip-line cusp at the punch surface is less than or equal to − k. Under these circumstances, it is predicted that thinning of the material at the punch will occur, which in practice would give a product with a reduced wall thickness and an increased internal diameter.
Nonlinear mechanical and thermal responses of a unidirectional carbon-fibre-reinforced plastic
Authors: Ditcher A K , Webber J P H 
Published: July 2007

Experimental results for unidirectional carbon-fibre-reinforced plastic (CFRP) are reported which show that the longitudinal stress-strain behaviour of this material is nonlinear elastic up to failure. The tangent modulus is found to reduce with increasing compressive strain, and to increase with increasing tensile strain. In addition, a small variation in Poisson's ratio with longitudinal strain is found. A specimen width of 5 mm (rather than the usually accepted 10 mm width) is used in order to reduce the likelihood of end effects being transmitted to the centre of the specimen. This is supported, to some extent, by a theoretical plane stress analysis using finite elements. A relatively simple method of measuring the thermal expansion of CFRP using suitably compensated strain gauges is described, and experimental results are given.
Rotating thin cylinder: Effect of small error in circularity
Authors: Holland M 
Published: July 2007

The error-modified, circular, mean-line form is represented by an elliptic profile and equations are developed for bending moment, tensile and shear forces resulting from inertia loading. It is shown that the maximum values of tensile force and bending moment both occur at the same location if the ratio of principal axes lengths is less than, or equal to, 1.09. For a cylinder having a mean-diameter-to-wall-thickness ratio of one hundred and with a difference in principal axes lengths of 0.1 per cent, the maximum stress is shown to be 1.33 times that in a perfectly circular cylinder. When the difference in the length of principal axes is increased to 0.4 per cent, this stress intensification factor increases to 1.75.
Method of fracture toughness evaluation of adhesive joints
Authors: Chow C L , Ngan K M 
Published: July 2007

This paper presents the development of a testing method for adhesive joints under Mode 1 fracture. The proposed testpiece consists of two slender beans with a ‘blister’ at the centre of each, which are bonded together and loaded in compression. The effect of buckling and the stability of crack propagation is analysed and found to be in satisfactory agreement with experimental observations. Equations for the evaluation of the fracture toughness based on the energy criteria are derived for the proposed test configuration. The results obtained using the method are checked with those from the DCB specimen and found to be satisfactory.
Least squares computation of the prestrain and work hardening parameters of sheet metal
Authors: Twizell E H , Adak I 
Published: July 2007

For most metals the load-extension and stress-strain graphs are too complicated for easy mathematical analysis, and empirical equations must be formed. One such equation, which is especially useful when large strains are experienced, is Swift's equation σ = A( B + ∊) n where ∊ and σ represent logarithmic strain and true stress, respectively. The prestrain and work hardening coefficient are represented by B and n respectively, and A is a constant for the metal being used. Non-linear least squares optimization methods are more accurate than elementary methods for computing A. B. and n from discrete data pairs (∊i,σi)i= 1,2,…, N (N≥3) determined experimentally, and a model is developed which adapts the Gauss-Newton and Levenberg-Marquardt algorithms for this purpose. Numerical results for a number of specimen sheets are reported, and comparisons of the reliability and efficiency of the two algorithms are made.
Variable-stiffness elastic base mechanism for model shear wall structures
Authors: Coull A , Adams N W 
Published: July 2007

A description is given of a simple mechanism which was developed to simulate a system of variable-stiffness elastic base supports for a coupled shear wall structure. A system of cantilevers was used to enable both vertical and rotational base flexibilities to be provided, the two being independently variable over the required range of relative stilesses. An example is given of the use of the system in a model investigation of a three-dimensional shear wall structure.
Anisotropic hardening theory and the Bauschinger effect
Authors: Rees D W A 
Published: July 2007

A review of anisotropic hardening theory is presented with particular reference to the Bauschinger effect in reversed torsion and anisotropic yield loci in σ, τ space associated with plastic shear strain history. The Bauschinger effect is obtained experimentally from a series of torsion tests on En3B steel tubes prestrained to a maximum of 10 per cent plastic shear strain. The effect, measured from the stress in reversed torsion at the proportionality limit, is analysed from the theory. It is shown to be consistent with experimental observations made on the translation and contraction of an initial yield locus, that are in marked contrast to the rigid translation of kinematic hardening rules. The degree of shear prestrain is shown to considerably influence the magnitude of the effect, an observation in full support of a theoretical Bauschinger parameter. The present test data together with existing published data for commercially pure aluminium 1100-F and the aluminium alloy Noral 19 S confirm that the controlling parameter is a scalar coefficient of plastic prestrain. The investigation supports a scalar function that is parabolic in the second invariant of plastic prestrain. The effect of yield point definition is examined and a comparison between theoretical and experimental yield loci is presented.
Stresses around large circular holes in uniform circular cylindrical shells
Authors: Bull J W 
Published: July 2007

An experimental and finite element analysis of a uniform cylindrical shell with a large circular cut-out is presented. In this analysis three hole sizes are considered, namely μ = 2.037, 4.084, and 6.344 (where μ = {[12(1 - y2)]1/4/2} × [ a/( Rt)1/2]), for loadings of axial compression, torsion and three point bending. The experimental results are the only ones available for cylindrical shells with large values of μ (except for one graph by Savin (1)†), while for three point bending there is no previously published theoretical or analytical results. Good agreement is found between the calculated and experimental stresses around the holes.
Steady-State stress distributions in circumferentially notched bars subjected to creep
Authors: Al-Faddagh K D , Fenner R T , Webster G A 
Published: July 2007

The paper describes a procedure, based on a finite element method, for calculating directly the steady-state stress distribution in circumferentially notched bars subjected to creep without the need for obtaining solutions at intermediate time intervals. Good agreement is obtained with relevant approximate plasticity solutions and with numerical calculations which approach the steady-state over a period of time from the initial elastic stress distribution. Also, the procedure is equally applicable to primary, secondary, and tertiary creep, provided the variables of stress and time are separable in the creep law. Results obtained for a range of notch geometries and values of the stress index, n, are reported. It is found for each profile that a region of approximately constant effective stress, σ, independent of n, is obtained which can be used to characterise the overall behaviour of the notch throat region when a steady-state is reached sufficiently early in life. An approximate method for estimating the maximum equivalent steady-state stress across the notch throat is also presented which does not require a computer solution.
Elastic stresses due to torque transmitted through the prismatic part of keyed connections part II: Effect of shape with usual fits and friction
Authors: Fessler H , Eissa M 
Published: July 2007

Models of 25 different shapes of keyed connections have been loaded by a large range of torques, using ordinary and frozen-stress photoelasticity. Empirical formulae have been derived for five contact points where the stresses are concentrated. These formulae give good predictions over the complete shape range of the metric and inch standards. The latter is consistently better than the former.
Experimental and theoretical correlations for elastic buckling of axially compressed ring stiffened cylinders
Authors: Ellinas C P , Croll J G A 
Published: July 2007

Re-examination of some 85 past experiments on the elastic buckling of axially loaded ring stiffened cylinders shows the existence of two distinctive behavioural regimes. Lightly stiffened cylinders, like isotropic cylinders, buckle into non-axisymmetric modes having long axial wavelengths at loads that are sensitive to the precise magnitudes of small initial imperfections. Heavily stiffened cylinders are characterised by snap buckling into axisymmetric modes which, for elastic behaviour at least, show only limited sensitivity to initial imperfections. Each of these characteristics is shown to be predicted by the recently developed ‘reduced stiffness analysis’ method, which, despite the relatively perfect nature of test specimens, predicts reliable lower bounds to the experimental scatter. Taken together with the previously demonstrated empirical validity of the reduced stiffness analysis for the prediction of buckling modes and lower bounds to buckling loads for both isotropic and stringer stiffened cylinders, the present comparisons provide further support to the recommendation that this method be considered as an alternative basis for future design.
Model studies on plate girders
Authors: Narayanan R , Adorisio D 
Published: July 2007

Tests on eighteen small scale models which simulate the elastic and post-buckling behaviour of plate girders when subjected to shear loading are reported and discussed. The models were fabricated of steel and Araldite; the major aim was to assess whether small scale models can be employed to study shear buckling problems. A secondary object was to examine whether araldite could be used for predicting the structural behaviour and ultimate loads of plate girders. The strength and post-buckling characteristics exhibited by steel models were found to be similar to those observed by earlier investigators on full scale girders. The test results of steel models have been compared with the theoretical predictions obtained by using some ten design methods developed in different countries. Most of these methods are shown to give conservative but satisfactory predictions of the ultimate shear capacity of the model steel girders. Tests on Araldite models demonstrated that post-buckling behaviour can be observed visually on account of the large elastic deformations which the material is capable of, before collapse. However, they were found to be unsuitable for the prediction of the ultimate shear capacity. As Araldite is brittle, collapse would occur prematurely by sudden fracture before the full development of the tension field.
The uniaxial and biaxial, monotonic and cyclic plasticity behaviour of a lead alloy model material
Authors: Hyde T H 
Published: July 2007

A chill-cast, antimony-arsenic-lead alloy model material has been used to investigate the monotonic and cyclic loading, uniaxial and biaxial plasticity behaviour of a metal at elevated temperature, i.e., T/ Tm ≈ 0.5. For the lead alloy used, a post-machining heat treatment of 96h at 100 C considerably reduced the scatter in the material behaviour. Uniaxial monotonic loading tests showed that the behaviour is relatively independent of temperature and strain-rate for strains less than about 1 per cent. Under cyclic loading conditions, between fixed strain limits, a stable hysteresis loop is obtained after the first cycle for both uniaxial and biaxial stress systems. By taking into account the biaxiality ratio and the increase in yield-range caused by cyclic hardening, the uniaxial and biaxial, cyclic plasticity behaviour was reasonably accurately predicted from the uniaxial, monotonic loading behaviour.
Reduction of stress concentration around a hole in a uniaxially loaded plate
Authors: Jindal U C 
Published: July 2007

The stress concentration around a circular hole in a plate can be reduced by up to 21 per cent by introducing auxiliary holes on either side of the original hole. But this approach of auxiliary holes creates two more regions of stress concentration in the plate. In the present study, the hole geometry has been modified to effect stress reductions as high as 22 per cent. The problem has been analysed numerically by the finite element method and experimentally by two-dimensional photoelasticity. It has been observed that by making the hole oblong in the direction of loading, a high order of reduction in stress concentration around the hole can be obtained.