Glynn Rothwell

Reference stress intensity factors with application to weight functions for internal circumferential cracks in cylinders

Abstract Stress intensity factors from finite element analysis, are presented for internal circumferential cracks in cylindrical components subjected to a range of through wall stress distributions. Cylinders with ratios of internal to external radii in the range 0.1 to 0.9 have been considered for a full range of dimensionless crack depths from 0.02 to 0.95. A set of weight functions for each of the cylindrical geometries has been developed and the accuracy of these has been examined using the finite element results. General conclusions have been drawn concerning the merits of the various types of weight function.

A comparison between the finite element and frequency response methods in the assessment of thermal striping damage

Abstract When incompletely mixed, hot and cold fluid streams pass adjacent to the surface of a component or structure, and cause thermal striping on the surface. The existing methods of assessment of the consequent thermal fatigue damage have been implemented in the computer codes CLOUDBURST, TBL and STRIPE, and these have been shown to be in good agreement. Analysis of temporally random striping is possible in two of the methods, whereas use of the finite element method in such a fatigue analysis may lead to impractically long run times. However, for the special case of sinusoidal patterns of striping, comparison is made in this paper between TBL and the finite element method for the assessment of thermal striping damage. A fully restrained, single edge cracked plate and a circumferentially cracked cylinder, axially restrained and unrestrained, have been subjected to sinusoidal surface striping for various representative temporal frequencies. The resulting stress intensity factor fluctuations have been determined for various crack depths using the finite element computer code ABAQUS and the analytical code TBL. Good comparisons have been obtained in all cases.

Finite Element Study into the effect of footwear temperature on the Forces transmitted to the foot during quasi- static compression loading

The determination of plantar stresses using computational footwear models which include temperature effects are crucial to predict foam performance in service and to aid material development and product design. Finite Element Method (FEM) provides an efficient computational framework to investigate the foot-footwear interaction. The aim of this research is to use FEM to investigate the effect of varying footwear temperature on plantar stresses. The results obtained will provide data which can be used to help optimise shoe design in terms of minimising damaging stresses in the foot particularly for individuals with diabetes who are susceptible to lower extremity complications. The FE simulation results showed significant reductions in foot stresses with the modifications from FE model (1) without footwear to model (2) with midsole only and to model (3) with midsole and insole. In summary, insole and midsole layers made from various foam materials aim to reduce the Ground Reaction Forces (GRFs) and foot stresses considerably and temperature variation can affect their cushioning and consequently the shock attenuation properties. The loss of footwear cushioning effect can have important clinical implications for those individuals with a history of lower limb overuse injuries or diabetes.

Effects of Temperature on the Performance of Footwear Foams Subjected to Quasi-Static Compression Loading

Diabetic ulcers are the most common foot injuries leading to lower extremity amputation [1]. Early detection and appropriate treatment of these ulcers may prevent the majority of amputations [2]. One of the most important factors in causing such injuries is the friction of the foot on the ground which produces heat and induces a non-homogeneous elevation of temperature in the foot. This elevation varies according to the kind of quasi – static and dynamic movements and to the ability of the footwear materials to evacuate the heat.

Effective stress factors for reinforced butt-welded branch outlets subjected to internal pressure or external moment loads

This paper presents finite element data for 92 reinforced butt-welded branch outlet piping junctions designed according to the ASME B31.3 process piping code, for the purpose of investigating their effectiveness in the light of data for un-reinforced fabricated tee junctions. The data suggest that the reinforcement provided under the ASME B31.3 design is effective for the internal pressure load case and all external bending moment loads with the exception of branch out-of-plane bending for thin-walled assemblies.

Filtering and analysis of accelerations and strains measured on a tie down system of a heavy nuclear transport package during a routine rail journey

Abstract The design and development of nuclear packages is critical for the safe transportation of new fuel and irradiated waste. The renaissance of the nuclear industry in recent years has increased motivation for the development of optimised transport and storage solutions. The design of mechanisms to safely constrain nuclear packages, commonly referred to as tie down systems, has become more challenging as package masses have increased. This paper focuses on characterising the loading environment that a tie down system is subjected to using signal processing techniques on previously measured acceleration and strain time histories. The measurements were taken on a tie down system for a nuclear package, weighing 99·7 tonnes, during a routine rail journey. Similar previous studies on tie downs have omitted frequency analysis of the measured signals on tie down systems. A frequency analysis has been used to determine the nature of the loading experienced by a tie down system and also the extent of vibration transmission into the package. A means for obtaining a suitable filter cutoff frequency is also presented by comparing frequency spectra from different measurement points. To extract quasi-static accelerations from the raw data, several digital filters have been designed to study their effects on the resulting signals. By comparing the low pass and band pass filtered time histories, some insightful trends in the accelerations peaks have been found. To demonstrate what constitutes a good or bad filter design, sensitivity studies have been conducted to show how the distributions of peaks and their statistics are altered significantly with poorer filter choices.

An experimental procedure for measuring accelerations and strains from a tie down system of a heavy nuclear transport package during a rail journey

Abstract The transportation of nuclear waste and new nuclear fuel is an important aspect in sustaining the generation of electricity by nuclear power. The design of packages that satisfy regulatory requirements for normal operating and accident conditions is a complex engineering challenge. The ancillary equipment used to constrain the packages to their conveyance, a tie down system, is part of a multicomponent system used to transport packages. Traditionally, the individual components of the transport system have been designed in isolation. This approach does not account for the interaction between components of the system such as the conveyance, tie down system and package. The current design process for tie down systems is well established but, due to its heuristic development, suffers from uncertainties over which loading conditions should be applied. This paper presents a method for collecting measured acceleration and strain data that can be used to derive customised load cases for the design of tie down systems during rail transportation. The data was collected from a tie down system that restrained an empty TN81 package, weighing 99·7 tonnes during a routine rail journey from Barrow-in-Furness to Sellafield. Furthermore, the data can be used to validate modern computer models, allowing for the development of the previously described holistic approach to tie down system design. The results are unique because an ensemble of acceleration and strain time histories from a transport system laden with a nuclear package is unprecedented. A visual examination indicates that the loading a tie down system incurs during a rail journey consists of low magnitude accelerations. The measurement points also show that the general trend of acceleration levels is highest nearest the track and is attenuated by the package. The implications for the design of tie down systems are that two potential failure modes, fatigue and static strength, have been identified. The data provides scope for customising accurate static strength and fatigue calculations using modern computational techniques. This allows for the safety margins inherent in new designs to be determined and optimised design solutions made possible. INS makes no representations or warranties or any kind concerning this article, express or implied, statutory or otherwise, including without limitation, warranties of accuracy or the absence of errors.

Numerical Study of the Effect of Welding Parameters on the Strength of Spot-Welded Joints

Resistance spot welding (RSW) is widely employed in sheet metal fabrication, in particular in automotive bodies and structures. Manufacturers are increasingly demanding reduced design periods with improved safety requirements, which could potentially be achieved through computational simulations. This paper presents an integrated approach combining simulation of the welding process, materials characterisation and mechanical modelling to study the effect of welding parameters on the strength of spot-welded joints. The welding process was simulated and the dimensional attributes were used to build the mechanical models for strength analysis. The constitutive material properties of the base, nugget and the heat-affected-zone (HAZ) were determined by an inverse FE modelling approach using indentation test data. The predicted deformation of spot-welded joints of a typical automotive steel under tensile-shear load showed a good agreement with experimental results. The validated models were further used to predict effects of welding parameters on the strength and failure behaviour of weld joints. Potential uses of the approach in optimising welding parameters for strength were also discussed.

Effects of Temperature on the Performance of Footwear Foams: Review of Developments

The human foot is a multifunctional system that serves as the primary physical interaction between the body and the environment during gait. Footwear foam components maintain efficient foot function which is essential for daily living and provide cushioning by acting as a protective layer between the foot and the ground that attenuates the shock of impact. Footwear foam materials have high temperature dependency mechanical characteristics. The lower the temperature, the less elastic the material becomes. Consequently, it would seem reasonable to expect different mechanical and cushioning characteristics for the same shoe under different temperature conditions. Although the footwear foam materials great temperature sensitivity and the clinical implications of excessive temperature rise in the footwear during activities on lower extremity injuries and ultimate amputation are well recognized, but very few studies have demonstrated this dependency. This study reviews the developments made on the temperature effect on the performance of footwear foams and assesses its consequent clinical complications.

How well does a linear static finite element analysis predict measured strains from a nuclear package tie-down system during rail transportation?:

Freight rail is often the preferred method for transportation of dangerous goods. One particular application is the use of rail to convey radioactive material in purpose-built packages. During transit, packages are secured to a rail wagon bed with a tie-down system. The design of tie-down systems varies considerably depending on the package type and rail vehicle; for example, shackles, turnbuckles, tie rods, gravity wells or transport frames are all commonly used. There are also a large number of different packages in existence that all vary in size and mass, typically 1–7 m in length and 100 kg–100 t in mass. Despite the uniqueness of many transport configurations, the design of tie-down systems is always carried out using a limited set of design load cases as defined in the appropriate Codes of Practice and Standards. Many authors have suggested that the load cases within the standards need revision or question which load cases should apply to which scenario. In a previous experiment, accelerations and strains have been measured on a freight wagon and transport frame of a heavy package during a routine rail journey. From these data, a new insight into the magnitude and nature of loading has been gained. In the present study, the measured accelerations have been used as input to a finite element model of the transport frame, and a method based on correlation between predicted and measured strains has been developed to determine an appropriate low-pass filter cut-off frequency, fc, which separates quasi-static loading from raw dynamic data. The residual dynamic measurements have been assessed using signal processing techniques to understand their significance. The finite element model has also been used to assess the presence of contact and boundary nonlinearities and how they affect the agreement between measured and predicted strains.