bluuebunny/crossref_metadata_2025 huggingface dataset:
Stress analysis of some nut-bolt connections with modifications to the nut thread form
Authors: Kenny B , Patterson E A
Published: July 2007

Six photoelastic frozen stress models of ISO nut-bolt connections loaded in pure tension were studied. Four of these models had modifications to the threads at the load bearing end of the nut. These modifications included tapered truncation of the thread crests and taper of the whole thread form for a portion of the nut length.

The maximum stress in the bolt always occurred within one pitch of the load bearing face of the nut. Truncating threads increased the maximum bolt stresses. Tapering the whole thread form reduced the maximum stress and produced a more uniform load distribution in the bolt.

The conditions at the load bearing face of the nut were found to influence the load distribution in the bolt threads more than the stress concentrations in the bolt.
Strain energy release rate for a circular-arc edge crack in a bar under tension or bending
Authors: Daoud O E K , Cartwright D J
Published: July 2007

A bar of circular cross-section is modelled with two-dimensional plane-stress finite elements. The bar has a crack at its edge, the front of which is a circular arc. The ends of the bar remote from the crack are subjected to either an axial load or a bending moment in the plane of symmetry of the cracked section. The strain energy release rate of the crack is determined from a finite element model as the rate of change of elastic energy in the bar for successive positions of the circular arc crack front. The values of strain energy release rate so determined are found to be comparable with existing results obtained from three-dimensional finite element analyses. The effect of curvature is found to cause a reduction in the strain energy release rate compared to that for a straight fronted crack of the same maximum depth in a bar under the same loading conditions. The results obtained are superimposed to obtain strain energy release rates for the circular are crack edge subjected to a combined tensile load and a bending moment.
Quantitative stress analysis by means of the thermoelastic effect
Authors: Stanley P , Chan W K
Published: July 2007

A new non-contact, full-field, stress analysis technique based on the measurement of the intensity of infra-red radiation emitted from the surface of a cyclically loaded body is applied to series of metallic specimens (including beams in bending, the ‘Brazilian’ disc, and a simple pure-shear testpiece) and critically appraised.
Fracture stresses for ± 75 degree filament wound grp tubes under biaxial loads
Authors: Highton J , Adeoye A B , Soden P D
Published: July 2007

Fifty, 100 mm diameter ± 75 degree filament wound E glass fibre/epoxy resin tubes have been tested to destruction under various combinations of internal pressure and axial tension or compression. The test equipment and procedures are described. The method of reinforcing and gripping the ends of the specimens avoided end failures. The effects of possible stress concentration at the ends are considered. Experimental fracture stresses are presented and compared with theoretical results for a variety of biaxial loading conditions.
Stress concentration factors of grooved shafts in torsion
Authors: Kato A , Mizuno T
Published: July 2007

The stress concentration factors at circumferential grooves in round shafts under torsion have been investigated by experiment. The copper electroplating method has been used to measure the stresses at groove roots. The experimental results are compared with Neuber's solution and the numerical values reported previously.
Creep of regain—rheologically simple hydrophillic polymers
Authors: Pecht M
Published: July 2007

For a class of materials called regain-rheologically simple, creep curves at various regain states can be shifted along the time axis in such a manner as to generate a single (master) curve. A constitutive model which exploits the unique time and regain-coupled creep response of these materials is presented. The model is then used to predict the creep response as a function of regain using experimental data obtained from a few simple tests on cellulosic handsheets.
Ratchetting tests of a stepped beam under steady tension and cycling bending
Authors: Fessler H , Hyde T H
Published: July 2007

Seven identical stepped beams, made of a lead alloy, were loaded by steady tension and cyclic bending. Three bending moments superimposing equal hogging and sagging were used in the tests. Six different tensions were also used. After test of 15 cycles, most beams were re-loaded with a greater mean tension and the same cyclic bending moment. Strains were measured in the (circular arc) fillets at the step and in the shank.

Ratchetting strains per cycle decreased during each test; steady values were estimated and related to the load magnitudes. The common use of the 0.2 per cent proof stress as the yield stress for an equivalent elastic-perfectly-plastic materials has been shown to be extremely conservative.
An experimental investigation of slow stable crack growth using hy130 steel
Authors: Etemad M R , Turner C E
Published: July 2007

Fracture toughness in terms of J and COD at or beyond initiation to ductile tearing were investigated using mainly three point bend pieces of HY130 steel in a variety of proportions. J values are adjusted for crack growth to obtain the resistance curve ( R-curve).

The R-curve was observed to become shallower with increasing width and thickness of test piece, and for longitudinal (TL) rather than short transverse (TS) crack propagation, but steeper with scaling to smaller absolute sizes, and decreasing thickness and width. For full thickness plates, the R-curve for tension was much steeper than bending. Discussion is given on the size requirements for a geometry independent R-curve, according to the present test data.
A study of the stress distribution in a lug loaded by a free fitting pin
Authors: Wearing J L , Arnell P P , Patterson C
Published: July 2007

The stresses in the lug of a pin-lug assembly can be easily calculated using a finite element model of the lug, provided the load distribution is known. Described in this paper is a technique which utilizes the finite element mesh of the lug to model the loading on the lug at the pin-lug interface. The technique has been incorporated into a finite element program which was then used to calculate the stresses in the lug. These calculated results, assuming a rigid pin and negligible friction between the pin and the lug, were compared with those obtained from a photoelastic study and agreement was found to be good.
An experimental study of simplified methods for the prediction of the deformation of structures subject to severe cyclic thermal loading
Authors: Ponter A R S , Jakeman R R , Morrison C J
Published: July 2007

The paper describes a set of thermal shock experiments on copper plates between room temperature and 250°C. The experimentally observed creep rates are compared with the predictions of two alternative simplified methods of analysis. The first involves rapid and slow cycle solutions which are computed using finite elements for two constitutive equations derived from the same constant stress data. The second involves upper bounds derived from shakedown solutions. It is shown that conservative results can be computed provided an appropriate relationship between average strain rate and cyclic stress history is known. The experimental data shows a sharp transition from a rapid cycle to a slow cycle condition as the load is increased above the high temperature shakedown limit.
Ratchetting rates for a bree cylinder subjected to in-phase and out-of-phase loading
Authors: Ng H W , Moreton D N
Published: July 2007

The work of Bree (1)† led to an understanding of the behaviour of a thin cylinder when subjected to an alternating through-wall thermal gradient together with a continuous internal pressure. Other physical situations require the same understanding when such a cylinder is subjected to these loads, but when both are cyclical in nature. We consider here the circumstance of the loads changing in-phase and out-of-phase. Bree type diagrams depicting zones of elastic, shakedown, plasticity, and ratchetting regimes are presented. A full analysis leading to ratchetting rates is given. It is found that for both in-phase and out-of-phase loading the ratchet rates are less than those given by Bree.
A modification to the theory for the load distribution in conventional nuts and bolts
Authors: Patterson E A , Kenny B
Published: July 2007

A discrepancy between experimental results and the generally accepted theory for the load distribution occurring in the threads of a nut-bolt connection is highlighted. This occurs at the loaded end of the bolt and is caused by the changing geometry of the thread form of the nut as the thread emerges from the loaded face of the nut. The result is a thread form which is not complete and which is progressively more flexible as the loaded face of the nut is approached. This results in a reduction of the load carried by these incomplete threads. Sopwith's analytical theory has been modified to allow for this effect by using finite element analysis to determine the varying stiffness of the threads. The results of this modified theory compare well with those from three-dimensional photoelastic analyses of the loads in the threads of two bolts fitted with conventional nuts.
Design-development of a variable load tension—compression creep testing machine
Authors: Morrison C J , Hayhurst D R
Published: July 2007

The design and development is described of a variable load tension-compression creep machine (±50 kN) which overcomes the disadvantages of servo-hydraulic and recirculating ball screw testing machines. The use of dead weight levers to apply specimen loads ensures the achievement of low running costs. Screwed end specimens are used with a 25.40 mm parallel sided gauge length and a diameter of 12.70 mm. It is shown that, provided modest rates of loading (0.4 kN/s) are used, high accuracy ‘through zero’ loadings can be achieved. The machine has been shown to operate satisfactorily for long periods under tension-compression high temperature creep.
Microcomputer design analysis of plate post-buckling behaviour
Authors: Rhodes J
Published: July 2007

Explicit formulae are presented for the examination of plate post-buckling behaviour. Plates with simply supported loaded ends and having simply supported, fixed, or some intermediate, elastic restraint on edge rotation are considered, and it is assumed that the unloaded edges are free to wave in their own plane. The coefficients used in the equations were derived on the basis of curve fitting to a large number of computer solutions and are applicable to any buckle half wavelength or rotational restraint condition normally found in engineering structures. These equations are sufficiently simple to provide extremely rapid predictions of plate behaviour on any small microcomputer.

Comparisons are made with some existing published results and the effects of imperfections, degree of edge rotational restraint, and buckle half wavelength are illustrated. The behaviour predicted for plates in the far post-buckling range is examined and shown in comparison with the design formula of von Karman. It is suggested that, for accurate plate design, strength and stiffness should be considered separately, and that the effects of rotational edge restraint should be taken into account in both buckling and post-buckling analysis.
The optimisation of the design of nuts with partly tapered threads
Authors: Patterson E A , Kenny B
Published: July 2007

The angle of taper and the number of tapered threads in a nut necessary to give the lowest maximum stress concentration in the bolt were determined for an ISO nut—bolt connection subject to axial loading. Thirty-eight frozen stress models were analysed and it was found that a two degree taper for 5.5 threads from the loaded face of the nut reduced the maximum normalised tensile stress in the bolt by 41 per cent from 5.17 to 3.07.

It was observed that if the angle of taper was too large the stress concentration produced at the junction of the parallel and tapered threads could negate the beneficial effects of the taper geometry.
A computerised design aid for drive shafts with some fatigue considerations
Authors: Walton D , Prayoonrat S
Published: July 2007

A method of designing power transmission drive shafts is described based on two interactive computer programs. The first program can model shafts of any configuration and under any system of loads and supports. The program is based on the finite element method. Reducing the size of the stiffness matrix by storing only the parameters in the matrix bandwidth and by overlaying the stiffness matrices, the problem of using finite element analysis on small memory microcomputers can be solved. A menu allows the designer to specify machine elements, such as spur or bevel gears or pulleys, to be positioned at any point along the shaft. The user can give information of the power transmitted, speed, and details of the physical dimensions of the machine elements which then enables the program to determine the force vectors and apply these to the shaft nodes.

The second program determines the design factors of safety on the basis of both static and cyclic loads. For cyclic loads the factors of safety are based on infinite-life design, using Soderberg and Goodman criteria. The program contains extensive built-in data on endurance strengths, factors influencing the endurance limit, and stress concentration factors.
Finite-Width correction factors for sen testing of orthotropic materials in opening mode
Authors: Sweeney J
Published: July 2007

Calculations of finite-width correction factors, Y, for mode I SEN tension testing of orthotropic materials have been made using a J integral implemented on results from finite element analyses. Y depends on the ratio of principal normal compliances S11/ S22 and another dimensionless quantity involving the material compliances. Aspect ratio is fixed at 1 and normalized crack depth varies between 0.3 and 0.6. S11/ S22 is fixed at four values; 20, 10, 1/10, and 1/20. Ranges of the other dimensionless material parameter relevant to existing materials are chosen. The use of linear interpolation for Y at intermediate values of S11/ S22, and the relevance of the results to specimens with aspect ratios in excess of 1, are discussed. Y is presented at each value of S11/ S22 in the form of a Chebyshev series in two variables. The results show that, if Y factors already established for isotropic materials are used to calculate stress intensity values for orthotropic specimens, errors in the stress intensity factor can be as high as 50 per cent.
Use of the reference stress concept to assess the effect of crack growth increment size on the accuracy of creep crack grow predictions
Authors: Hyde T H , Low K C
Published: July 2007

An approximate method, based on the reference stress concept, for carrying out ‘moving-crack’ calculations, under creep conditions, is presented. Creep crack growth is assumed to be related to the C∗ parameter. The predictions obtained correlate well with detailed, ‘moving-crack’, finite element calculations.

Preliminary calculations, to assess the adequacy of finite element meshes and the effect of variations in material properties on the accuracy of predictions, can be carried out quickly and relatively cheaply. The usefulness of the technique is illustrated by using it to show the effect of the magnitude of the crack growth increment assumed and of the value of critical crack tip opening displacement (the initiation parameter assumed) used.
Probability of failure calculations and confidence band estimates for an annular brittle disc fractured under centrifugal loading
Authors: Cooper N R , Margetson J , Humble S
Published: July 2007

Monte Carlo simulation techniques are used in conjunction with the pivotal quantities of the two parameter Weibull distribution (or three parameter Weibull distribution with prescribed threshold stress) to calculate confidence bands for the probability of failure of thin annular discs subjected to centrifugal loading. The theoretical predictions, assuming either volume or surface defects govern failure, are compared with experimental fracture data.
Nomographic design procedures for fibre-reinforced metallic rocket motor cases
Authors: Groves A , Margetson J , Stanley P
Published: July 2007

Nomographic design procedures are developed for a metallic cylinder (e.g., a rocket motor case) circumferentially reinforced with a pre-strained elastic fibre overwind. Techniques for calculating the pressure for first yield in the metallic case and the optimum winding conditions are presented, together with a technique for determining the maximum fibre stress.

Design examples are presented with each nomogram in turn and the graphical results are compared with exact numerical values.
Optimization of stiffened panels under compression
Authors: Weiji Li
Published: July 2007

The optimization of the angle-stiffened panel under compression using the feasible direction method is studied in this paper. We could only take the most critical constraint into account for each iteration when using the feasible direction method, with the result that the process of calculation is greatly simplified. It is beneficial for stability and convergence of the design process that the design variables in each iteration are modified once by some experience formulae, if necessary. The illustrative examples and the comparison of the numerical results of this paper with those of another paper indicate the effectiveness and efficiency of the method presented here.
Stress redistributions in thick-walled cylinders due to the introduction of a cross-bore after autofrettage
Authors: Tan C L
Published: July 2007

The numerical boundary integral equation method for three-dimensional elastostatics is employed for the stress analysis of a thick-walled cylinder with a radial cross-bore. The geometries considered are for cylinders with radius ratio k = 2.0 and 2.25, and with the cross-bore radius one-quarter that of the cylinder bore. Results showing the elastic stress distributions in an internally pressurized un-autofrettaged cylinder with the radial hole are presented. Using the classical superposition principle, the stress redistributions in partially autofrettaged tubes, due to the introduction of a cross-bore after autofrettage, are also obtained. The maximum percentage overstrain that can be induced in the cylinder with k = 2.0 without re-yielding occurring when the radial hole is introduced, is found to be only 35 per cent. The corresponding percentage overstrain for the cylinder with k = 2.25 is 27.5 per cent. From the computational results, it is also found that the variations of the resultant residual hoop stresses across the cylinder wall near the cross-bore and in the radial plane containing its axis, may be represented by a bi-linear form. Further, the limiting internal pressure that the vessel can sustain without re-yielding occurring, is not increased if the process of autofrettage is applied prior to the introduction of the cross-bore.
Loads, Stresses, and deflections in Bicycle Frames
Authors: Soden P D , Millar M A , Adeyefa B A , Wong Y S
Published: July 2007

A bicycle frame has been analysed as a three-dimensional framework and stresses and deflections predicted using a finite element computer program. Theoretical results for simple loading case were compared with strain gauge measurements in laboratory tests.

More complex loading cases representing common cycle racing situations were analysed. The largest stresses in the frame were bending stresses. Stresses in the region of 300—400 MN/m2 were predicted in the down tube and right chain stay during starting and stresses of about 250 MN/m2 at the front of the top tube and down tube during severe braking.
Non-linear finite-element analyis on microcomputers for metal forging
Authors: Hussin A A M , Hartley P , Sturgess C E N , Rowe G W
Published: July 2007

In recent years microcomputers have become more powerful and for some purposes are now able to compete with minis and mainframe computers. It is now possible to implement a wide variety of CAD packages and linear finite-element stress analysis programmes on microcomputers, but the solution of non-linear problems - for example, forging - is more complex.

This paper shows that a microcomputer can, nevertheless, be used for the analysis of a bulk metal forming process where there are both geometric and material non-linearities. The programs give reliable estimates of metal flow, grid distortions, stress, and strain distributions in the workpiece, as well as the forming force. An elastic-plastic finite-element method is used, with SSS-Fortran as the computing language. The results of such simulations can be used in-house to form the basis of improved forging die design, and, hence, a better final product, without the need for much of the expensive and time-consuming experimental trials currently practiced in industry.
Design formula for grooved shafts under torsion
Authors: Kato A
Published: July 2007

A design formula has been derived to estimate stress concentration factors of grooved shafts with several kinds of groove shapes. This formula was based on the analytical result for infinitesimal grooves and for finite grooves the experimental values found by the author and others, with the numerical values found by other investigators. Over a wide range of groove sizes, the formula agrees fairly well with the numerical values of Nishitani et al. Comparison with Neuber's formula shows that his formula gives much lower values than the present one, especially for deep grooves.
An assessment of the effects of prestrain on upper shelf fracture toughness
Authors: Ainsworth R A
Published: July 2007

The effects of prestrain on the fracture toughness of steels are examined by using a simple cumulative damage model of microvoid growth and coalescence. First the effects of a shear prestrain on the mode III toughness at a single temperature are calculated in order to obtain guidance on how best to approximate the stress—strain curve after pre-strain. Then the models are used to examine the influence of a uniaxial pre-strain on the values of mode I toughness on the upper shelf. The mode I analyses require crack tip blunting solutions, and it is demonstrated that an approximate blunting solution enables the models to be applied readily. Numerical results for various amounts of pre-strain are calculated by taking material properties typical of an A533B steel. It is found that the effects are generally small for the material properties considered.
Stresses in swivel ring flanges due to pressure loading
Authors: Hyde T H , Marsden B J
Published: July 2007

Finite element and photoelastic methods of stress analysis have been used to study the effects of pressure loading on the behaviour of swivel ring flanges. The use of recesses on the back faces of flanges, to control the load position, were investigated. The effect of the friction conditions between the flange and ring were also considered. It was found that the inclusion of a recess can significantly reduce the highest stresses, which occur in the flange/hub fillet radius. The friction conditions between the flange and ring were also found to have a significant effect on the stresses.
C∗ correlations for creep crack growth in weld metals
Authors: Gooch D J , Kimmins S T
Published: July 2007

Creep crack growth tests have been performed on compact tension specimens of 2 1/4CrlMo, C—Mn, and AISI 316 weld metals at 565°C, at 360 and 390°C, and at 600°C, respectively. The data have been analysed in terms of the C∗ creep parameter obtained directly from experimental measurements and by use of estimation formulae which depend on uniaxial creep data and evaluation of a reference stress. When expressed in the form d a/d t = D C∗ q the two approaches result in correlations which differ both in the constant, D, and in the exponent, q.

The differences in the constant may be largely rationalized in terms of the constraint on deformation appropriate to the test conditions and the effects of this on the reference stress.

The exponent, q, was generally lower when the estimation formulae were used than when C∗ was calculated from measured displacement rates. This was attributed to the lower stress dependence of the load-line displacement rates of the compact tension specimens compared with that of the uniaxial minimum creep rate at similar stress levels. This arises because primary creep strains may dominate the overall deformation behaviour of a compact tension specimen for many practical circumstances.
An experimental technique for determining the flexibility of tubular joints in offshore structures
Authors: Fessler H , Mockford P B , Webster J J
Published: July 2007

A test procedure has been developed and used for determining the flexibility of tubular joints. The manufacture of Araldite model joints, the method of testing these joints, and the analysis of the test results to obtain flexibility matrices are described.
Evaluation of stiffened shell characteristics from imperfection measurements
Authors: Abramovich H , Yaffe R , Singer J
Published: July 2007

The measurement of initial geometric imperfections of stringer-stiffened cylindrical shells on a laboratory scale is reviewed and recent results are presented. Buckling loads are predicted by the multimode analysis and are compared with experimental results. The concept and purpose of an international imperfection data bank is outlined and the activity of the Technion branch is described. An evaluation of the characteristics of shells from their measured imperfection record is attempted.
A micropolariscope for automatic stress analysis
Authors: Fessler H , Marston R E , Ollerton E
Published: July 2007

A micropolariscope has been developed for the automatic analysis of photoelastic data. It will position frozen stress slices mounted on its stage to within ±0.002 mm, and takes readings of isoclinic angles and fractional fringe orders, repeatable to within ±0.08 degrees and ±0.001 fringes. A rectangular grid of up to 3 × 50 points can be read automatically, taking about 1¼ minutes per point; the readings are stored on a floppy disc and printed out.

The original slice is itself sliced, and the subslice is viewed again in the orthogonal direction to produce a second set of readings. Software has been devised to analyse the two sets of readings. It makes use of Tesar's modification of Frocht's Shear Difference method to calculate five cartesian stresses, which may be plotted and printed in tabular form. Flexible facilities are provided for editing, correcting, plotting, and printing intermediate stages in the analysis, and for storing results in data files
Design of an end face seal assembly for lubricated rotary joints
Authors: Dragoni E , Strozzi A
Published: July 2007

A novel end face seal assembly composed of a rubber load ring, a metal stiffening ring, and a rubber seal ring serially connected together is presented. The design procedures adopted to achieve good operational effectiveness and long wear life are discussed in detail. Particular attention is focused on obtaining a load ring exhibiting a linear load-deflection relationship, and a seal ring capable of producing a semi-elliptical pressure profile at the sealing lip. These requirements are met by acting on the cross sectional shape of the rings. A comparison between well-correlating theoretical, numerical, and experimental results is given for both the elastomeric components.
A failure model for corded composite plates with edge fractures
Authors: Harrison A
Published: July 2007

The tensile strength of composite plates with unidirectional cords depends on the way the load is distributed within the matrix by the cords. Of particular interest is the effect of a broken edge cord or a number of in-line fractured edge cords on the breaking strength of the plate when it is subjected to axial loading. This paper describes a model for estimating the maximum allowable number of broken tensile members in a bonded composite plate before catastrophic failure occurs. The model has application to the analysis of steel-cord and Kevlar-cord elastomer belts containing broken edge cords as the result of impact damage.
Elastic stress concentrations in a square plate with a large hole under uniaxial loading
Authors: Shilkrut D , Uziel A , Gruntman S
Published: July 2007

The elastic stress concentrations in an infinite plate with a circular central hole which is loaded uniaxially, is a classical problem in the theory of elasticity. The aim of this work is to investigate the stress concentration phenomena in a uniaxially loaded square plate with a large central circular hole. Various load distributions on the external boundary are discussed. As a result of the numerical method and the experimental work, carried out on photelastic models, interesting stress distributions were found. (1) Both compressive and tensile stresses were found in the minimal section perpendicular to the direction of the acting load in the cases of either tensile or compressive loading. (2) In the case of a nearly concentrated load, the maximal stress appears at the intersection of the hole with the loading axis. The numerical method used here can easily be generalised for the study of other problems of plane elasticity and thermoelasticity of either isotropic or anisotropic bodies.
Enhancing finite element surface stress predictions: A semi-analytic technique for axisymmetric solids
Authors: Richards T H , Daniels M J
Published: July 2007

This paper describes the formulation and implementation of a semi-analytical procedure for enhancing finite element surface stress predictions. The efficacy of the process is demonstrated by application to a variety of test cases.
Stress analysis of some nut-bolt connections with modifications to the external shape of the nut
Authors: Patterson E A , Kenny B
Published: July 2007

The effect on the stress levels in an axially loaded bolt has been investigated for the case where a nut which incorporated a circumferential groove in its outer surface was used. It was found from a three-dimensional photoelastic frozen stress study that the modified nut reduced the maximum stress in the bolt by 5 per cent. The addition of a bevel to the load bearing face of this nut further reduced the maximum stress to 74 per cent of its value in a standard connection. It has been established that these modifications reduce the maximum shear stress in the roots of the nut threads, and that the stress concentration associated with the groove was smaller than the maximum stress concentration in both the nut and bolt thread roots. The increase indicated by photoelastic analyses in the strength of the connection produced by these modifications, has also been substantiated by fatigue tests of steel connections, but these results are not reported in this paper.
Elastostatic analysis of problems involving complex toroidal geometries
Authors: Colle A R , Redekop D , Tan C L
Published: July 2007

The three-dimensional boundary integral equation (BIE) method is used to solve two elastostatic problems involving complex toroidal geometries. The first problem concerns a thick-walled 180 degree pipe bend connected to tangent pipes, subjected to in-plane bending and internal pressure. Results are presented for stresses and are compared with results from previous numerical and experimental work. The second problem concerns a thick-walled pressurized torus, with cross bores situated in the toroidal plane. Separate solutions are given for cross bores located at the intrados and extrados of the torus. Results are presented for the stress concentration factor, and are compared with numerical work for thick-walled cylindrical pipes.
An improved boundary element formulation for calculating stress intensity factors: Application to aerospace structures
Authors: Aliabadi M H , Rooke D P , Cartwright D J
Published: July 2007

In order to compute stress intensity factors accurately, the standard boundary element method is modified to take explicit account of the singularity in the stresses at a crack-tip. The known expansion terms of the crack tip displacement and stress fields are subtracted to remove the numerical difficulties associated with the representation of a singular stress field at the crack-tip. Hence the accuracy of calculation is much improved, without appreciably increasing the amount of computation involved. Furthermore, the stress intensity factor is directly obtained as a part of a solution and no extrapolations are required. The improved formulation is applied to a configuration, which is representative of a part of the wing in a civil transport aeroplane. This configuration consists of a pair of circular cut-outs (supply ports) near to which smaller holes exist; these small holes are particularly susceptible to cracking.
Limit pressures for spherical vessels with radial branches of differing protrusion lengths
Authors: Robinson M , Kitching R , Lim C S
Published: July 2007

The effectiveness of the length by which a radial branch pipe extends within a spherical pressure vessel is discussed with reference to the plastic limit pressure of the vessel and the design rules of BS 5500. Lower bound limit pressures are calculated using a non-linear programming method, the stress resultants being expressed in polynomial form. The material was assumed to be rigid-plastic and to obey the von Mises yield criterion.
The analysis of elastic stress distribution in threaded tether connections
Authors: Newport A , Topp D A , Glinka G
Published: July 2007

A technique is presented for predicting the load distribution and local stress distribution in threaded tether connections. The load distribution is derived by modelling the connection as a system of springs and beams. This distribution is then used in conjunction with the appropriate stress concentration factors derived by the finite element method to obtain the local stress distribution.

A comparison is made between the theoretical predictions of local stress and published experimental results obtained from a photoelastic model.
On the numerical solution of line contact problems involving bonded and unbonded strips
Authors: Jaffar M J , Savage M D
Published: July 2007

This paper investigates the contact problem in which an elastic strip is indented by a rigid body (punch) of arbitrary shape. Both bonded and unbonded strips are considered.

A numerical method due to Gladwell (1)† is shown to be a direct and effective technique for analysing the effect of any punch whose profile is a polynomial of degree n, over a range of a/t (semi-contact width to a depth ratio) which is of practical interest 0 ≤ a/t ≤ 10 for Poisson's ratio 0 ≤ v ≤ 0.5.

For the cylindrical punch results are presented and compared with Meijers' asymptotic analytic solutions (2). For small a/t agreement is very good as expected. For a/t large, however, there are some large discrepancies which can be traced to an error in Meijers— expression for pressure distribution when v ≠ 0.5. Results are also presented for both the flat and the linear punch.
Axial–Torsional interactions and wire deformation in 19-wire spiral strand
Authors: Utting W S , Jones N
Published: July 2007

Tensile tests were performed on a straight steel strand of three layer (12/6/1) construction, having a core wire diameter of 3.66 mm and 3.33 mm diameter helical wires, under conditions of full end-fixity, partial restraint, and ends free from torsional restraint. The torque generated under tensile load was recorded as well as the strand extension and rotation over a 600 mm gauge length. Wire tensions and bending moments in the outer layer of helical wires were determined at the mid-strand position from the outputs of strain gauges in groups of three with parallel grids and mounted parallel to the wire axis on the crown of each wire.

The rate of strand extension under tensile load was found to be greater in tests with reduced torsional restraint, the greatest rate occurring in the free-end test. The strand rotation rate was also found to be greatest in the free-end test. The greatest difference from the theoretically predicted rates occurred in a free-end test with increasing load; predicted values of extension and rotation underestimated the test results by 12 and 23 per cent, respectively. Displacement of the load-torque plots occurred in the direction of reducing torque as testing proceeded. This appears to indicate the redistribution of the strand load between the layers of wires.

Wire tensions showed a more even sharing of load in the fixed-end condition than in the free-end condition. The increase in rate of tension with strand load was less for most wires in tests with reduced torsional restraint, with the lowest tension rates developing in the free-end condition.

For most wires, the rate of bending moment change with strand load was greater (in the sense tending to decrease tensile stress on wire crowns) in tests with reduced torsional restraint. However, the bending moment rates varied greatly between wires, the variation being greater in tests with reduced torsional restraint than in fixed-end tests.
Fracture mechanics characterisation of crack growth under creep conditions
Authors: Hollstein T , Kienzler R
Published: July 2007

Creep crack growth rates in the 32%−Ni−20%−Cr alloy Incoloy 800 H at 800°C are correlated with the fracture mechanics parameter C∗ integral. This was done by experimental and numerical investigations of different specimen sizes and geometries under constant load, constant rate of crack opening displacement or crosshead displacement, or slow cyclic loading. In the numerical simulations plane and three-dimensional finite element calculations have been performed without consideration of creep crack growth.
Contributions of rider-induced loads to bicycle frame stress
Authors: Hull M L , Bolourchi F
Published: July 2007

Presented in this paper is a new method for design analysis of bicycle frames. The new method relies on measurements of rider induced loading to perform a stress analysis of a bicycle frame. The vehicle for the stress analysis is ANSYS, a commercially available finite element code. Through application of individual measured loads, the method examines the corresponding nodes of maximum stress. Polar plots are developed to illustrate the variation of stress as a function of crank arm angle. Polar plots are also developed for the nodes experiencing the maximum total stress. Such a procedure enables the contribution of individual measured loads to the maximum stress to be ascertained. With this information, not only are the important loads for design analysis identified, but also the structural members of relative high and low stress are determined. Accordingly, these results have application to the detailed design of individual structural members.

To illustrate the new method, stress analysis of an aluminum frame is undertaken. The loading data are derived from an earlier study by the authors where significant seat, handlebar, and pedal loads were measured together with absolute pedal position. The loading data simulate that of steady-state cycling over flat terrain at about 9 m/s (20 mile/hr). The node of maximum total stress under steady-state loading is found to be the intersection of the top and seat tubes. Inasmuch as frames typically fail in the area of the bottom bracket (i.e., intersection of down and seat tubes), this result contradicts experience. This contradiction is explained by observing that the alternating stress/mean stress ratio is significantly greater for the bottom bracket area.
An approximate analysis of infinitesimal deformations of bonded elastic mounts
Authors: Shariff M H B M
Published: July 2007

An approximate simple theoretical solution is developed for infinitesimal plane and axisymmetric strain deformations for blocks of elastic material with Poisson's ratio between 0 and 0.5 bonded to rigid end plates. The explicit form of solution, developed for shape factor, S, between 0 and ∞, is easy to use and compares well with published experimental results. It is also comparable with previous theoretical investigations and expected behaviour.
Angular dependence of dynamic load transfer due to explosive loading in granular aggregate chains
Authors: Shukla A , Zhu C Y , Sadd M
Published: July 2007

An experimental investigation was conducted to study the dependence of packing geometry on the dynamic load transfer in two dimensional granular aggregate chains. The granular media was simulated by circular discs made of photoelastic material. The experimental method utilizes the combination of high speed photography and photoelasticity to visualize the dynamic load transfer phenomenon in two dimensional model chains subjected to explosive loading. The photographs thus obtained were analysed to get the normal and tangential loads at the contact points as a function of time. The results indicate that the load transfer is strongly dependent on the angle between the vectors drawn from the mass centres of the contacting granules.
The application of thermoelastic stress analysis techniques to composite materials
Authors: Stanley P , Chan W K
Published: July 2007

The application of the thermoelastic technique (SPATE) to two different composite material specimens is described and the results are critically discussed. The relevant theory, which permits a quantitative interpretation of the thermoelastic response from orthotropic materials, is outlined.
A photoelastic study of tool stresses caused by unsteady, shear localised chip formations during machining
Authors: Brown C J , Hinds B K
Published: July 2007

In the high speed machining of metals it has been established that the shearing process is frequently non-uniform resulting in a serrated chip with highly localised shearing. This type of chip formation is promoted solely by the properties of the material being machined and is not initiated by vibrations or resonances of the machine structure. It has been found that this type of unsteady, shear localised chip form can be duplicated when polyethylene is machined at low speeds with araldite cutting tools. By means of a photoelastic technique the variations in tool stress associated with these non-uniform chip forms has been revealed during the machining process. The photoelastic results clearly show that the tool stresses oscillate in a regular manner during the formation of each chip segment. The results obtained have lead to a better understanding of the chip formation process and provide a more complete description of the stress conditions experienced by the cutting tool.
Theoretical fringe analysis for a coherent optics method of residual stress measurement
Authors: Nicoletto G
Published: July 2007

In this paper, the theoretical relationships between relieved in-plane displacements and residual stresses, which are needed for data reduction in a moiré interferometric version of hole drilling method, are obtained. The analysis includes the case of linearly varying biaxial stresses. The theoretical relationships are then used for generating on a computer the corresponding moiré interferometric fringe patterns thus simulating the experimental response under known loading conditions. Various effects due to the degree of residual stress biaxiality, the strength of the linear stress term, the direction of sensitivity of the moiré grid, and the value of the Poisson's ratio are illustrated.
A strain-based tensor polynomial failure criterion for anisotropic materials
Authors: Zhang W , Evans K E
Published: July 2007

A strain-based tensor polynomial failure criterion for anisotropic materials is proposed with explicit derivations given in both strain and stress space. The physical distinction between this strain-based criterion and the current stress-based tensorial criterion of Tsai and Wu, is clarified. The viability of the proposed criterion is shown by its application to a graphite—epoxy resin lamina under plane stress. The allowed loadings and failure envelope of this lamina are predicted. Comparison is made with existing failure criteria (both stress-based and strain-based), in particular the maximum stress, maximum strain, and Tsai-Wu criteria.
GRP pipe bends subjected to out-of-plane flexure with and without pressure
Authors: Kitching R , Myler P , Tan A L
Published: July 2007

Out-of-plane bending tests were carried out on eight E-glass reinforced polytester resin, 90 degree pipe bends of 250 mm diameter and 250 mm bend radius. Each bend specimen tested had 1175 mm long tangent pipes attached, and construction was by hand lay-up, the glass being in the form of chopped strand mat (either 2.4 kg/m2 or 3.6 kg/m2). In all cases low loads were applied so that deformations were sensibly linear. Strains and displacements were measured and distributions were compared with estimates calculated from pipe bend theory for isotropic materials under plane stress, but modified for composites by using separate moduli for direct and bending stress conditions. Further measurements were taken for internal pressure (only) loadings on five of the specimens, and finally for out-of-plane flexure loading combined with constant pressure. Again measured values were compared with theory. Results are discussed in relation to a typical design procedure for such pipe components.
Effect of changes in elastic constants on the strength of composites
Authors: Zhang W , Evans K E
Published: July 2007

Tensor polynomial, maximum stress, and maximum strain criteria are considered in an investigation of the effect of varying elastic constants on the failure strength of composites. By expressing each criterion in the alternative stress or strain space they are made explicitly dependent on elastic constants as well as strength parameters. The significance of this result is highlighted by an example of the variation in failure envelope produced by altering the Poisson's ratio of the composite material. In particular the failure envelopes for a high strength graphite/epoxy resin (SP-286/T300) composite lamina are examined as a function of variations in the material's Poisson's ratio. The limits in the variation of the Poisson's ratio for this composite lamina are identified.
Stress concentrations at holes in thin rotating discs
Authors: Ang H E , Tan C L
Published: July 2007

The problem of a circular disc with a central hole and a symmetrical array of non-central holes subjected to rotation and to radial tension at its outer circumferential periphery is analysed using the boundary integral equation method. A relatively wide range of geometric configurations is considered. It is found that for this range treated, the peak stresses, which occur at the edge of the non-central holes, decrease in a linear manner with the number of holes, given the disc radius ratio and the radial position of these holes. These stresses are thus presented in terms of first order algebraic equations with the coefficients obtained using the least-squares-fit procedure.
Plastic-Elastic strains in two-dimensional sections of partial-penetration fillet welds
Authors: Fessler H , Pappalettere C
Published: July 2007

The photoelastic coating technique was used to study plastic strains at the orthogonal intersections of plates, formed by welding two side plates, without weld preparation, to a main plate. Models were cut from this weldment, perpendicularly to the planes of the plates. These models were loaded by tension and pure bending applied to the side plates. Although yielding starts at the weld toes, it remains constrained there due to the greater strength of the heat-affected zone. Plastic collapse occurs in the ‘parent’ plate. This phenomenon is due to the heat affected zone, not due to the notch formed by the weld.
Stress intensity calibrations for closed cracks
Authors: Hills D A , Nowell D
Published: July 2007

A powerful method is described for determining stress intensity factors for plane cracks intersecting a free edge and where the bulk stress field is such that the crack faces are pressed together along at least part of their length. This configuration occurs widely in problems where the crack is propelled by a contact stress field, but the simpler example given here for illustration purposes involves a cracked column undergoing compression and shear.