Philip Sewell

The development of laminated composite plate theories: a review

This study investigates and reviews approaches to modelling laminated composite plates. It explores theories that have been proposed and developed and assesses their suitability and functionality. The particular focus in this study has been on normal stresses and the through-thickness distributions of transverse shear. These are important for composite plates as stress-induced failures can occur in three different ways. Therefore, it is essential to understand and calculate transverse shear and normal stress through the thickness of the plate accurately. In this study, previous laminated composite plate theories are categorised and reviewed in a general sense, i.e. not problem specific, and the advantages and disadvantages of each model are discussed. This research mainly focuses on how accurate and efficient the models can predict the transverse shear. It starts with displacement-based theories from very basic models such as Classical laminate plate theory to more complicated and higher-order shear deformation theory. Models are furthermore categorised by how the models consider the overall laminate. In this article, the theories are divided into two parts: Single layer theory, where the whole plate is considered as one layer; and Layerwise theory, where each layer is treated separately. The models based on zig-zag and Discrete Theories are then reviewed, and finally the mixed (hybrid) plate theories are studied.

Developments in the trans‐tibial prosthetic socket fitting process: A review of past and present research

A revolution in transtibial prosthetic design began at the end of World War II with the development of new materials and a dramatic improvement in the understanding of biomechanics. Early research was based mainly on the improvement of existing prosthetic design practice. Today, research has been focused on providing a better understanding of stump/socket interface biomechanics and improving socket fit by attempting to quantify the normal/direct stresses at the interface. The purpose of this review paper is to question whether research and prosthetic education/training to date has significantly improved our understanding of what makes a good socket. Although there is no doubt that advances in socket fitting techniques have been made what is not clear is the actual extent to which these advances have improved the quality of sockets fitted. It is suggested that a new approach is needed which can overcome some of the inherent problems of designing and manufacturing a comfortable high quality socket. It is also suggested that current research and education/training in the fields of pressure/interfacial interaction measurement and Finite Element Analysis techniques have limited potential to address many of these problems. There is also little evidence that current computer aided design systems offer any significant advantages over more conventional techniques.

The design of lower‐limb sports prostheses: fair inclusion in disability sport

Within lower‐limb disability running, the design of the prosthesis has shifted from being a tool for restoring function to one of enabling athletes to perform to near non‐disabled standards. This paper examines the background to this development. The authors argue that the impact of technology on the design of prostheses is likely to affect athletes’ abilities and unfairly advantage those who are able to access the most recent innovations. It is shown that historically in the case of lower‐limb sports prostheses, some variation in their performance is evident. The sports legislation does not allow for this difference. It is indicated that these observations are of concern to the sports stakeholders and therefore warrants further attention. It is suggested that the full understanding of the prostheses contribution may never be known. The authors propose a synthesis of quantitative performance data and a qualitatively obtained code of values to help police these concerns.

Performance enhancement of bi-lateral lower-limb amputees in the latter phases of running events: an initial investigation

Current methods of evaluating the performance of a runner using an energy return prosthesis often rely on a physiological methodology, making the differentiation between the contributions from the biological and the prosthetic elements of the below-knee amputee athlete difficult. In this paper a series of mass and composite foot systems were used to evaluate the effect that gravity, mass, stiffness and inertia have on the dynamic characteristics of a prosthesis. It is demonstrated that if the natural characteristics of a system are identified and synchronised with the physiological gait behaviour of a runner, performance enhancement can occur, resulting in a faster take off speed and in storing extra energy in the system that can later be recovered. Therefore, a bi-lateral amputee athlete with near symmetrical gait can recover the stored energy during the steady state or latter phases of a running event.

Optimum Design of Fibre Orientation in Composite Laminate Plates for Out-Plane Stresses

Previous studies have shown that composite fibre orientations can be optimised for specific load cases such as longitudinal or in-plane loading. However, the methodologies utilised in these studies cannot be used for general analysis of such problems. In this research, an extra term is added to the optimisation penalty function in order to consider the transverse shear effect. This modified penalty function leads to a new methodology whereby the thickness of laminated composite plate is minimized by optimising the fibre orientations for different load cases. Therefore, the effect of transverse shear forces is considered in this study. Simulated annealing (SA) is used to search for the optimal design. This optimisation algorithm has been shown to be reliable as it is not based on the starting point, and it can escape from the local optimum points. In this research, the Tsai-Wu failure and maximum stress criteria for composite laminate are chosen. By applying two failure criteria at the same time the results are more reliable. Experimentally generated results show a very good agreement with the numerical results, validating the simulated model used. Finally, to validate the methodology the numerical results are compared to the results of previous research with specific loading.

Improvements in the accuracy of an Inverse Problem Engine's output for the prediction of below-knee prosthetic socket interfacial loads

The monitoring of in-service loads on many components has become a routine operation for simple and well-understood cases in engineering. However, as the complexity of the structure increases so does the difficulty in obtaining an acceptable understanding of the real loading. It has been shown that it is possible to solve these problems by interfacing traditional analysis methodologies with more modern mathematical methods (i.e. artificial intelligence) in order to create a hybrid analysis tool. It has, however, been recognised that an Artificial Neural Network (ANN) predicts poorly in the high and low ranges of the envelope of which it is trying to predict. This paper presents results of research to develop the ANN Difference Method to improve the accuracy of the Inverse Problem Engines output. This method has been applied to accurately predict the complex pressure distribution at the residual limb/socket interface of a lower-limb prosthesis. It has been shown that application of the ANN Difference Method to the output of a backpropagation neural network can reduce inherent errors that exist at the low and high ends of the ANN solution envelope. This powerful approach can offer load information at high speed once the relationship between the loading and response of the component has been established through training the ANN. Utilising an experimental technique combined with an ANN can provide in-service loads on complex components in real time as part of a sophisticated embedded system.

Modal analysis of composite prosthetic energy-storing-and-returning feet: an initial investigation

The desire of individuals with a lower-limb amputation to participate in sports, coupled with the high demands of athletics, has resulted in the development of energy-storing-and-returning feet, capable of storing energy during stance and returning it to the individual in late stance to assist in forward propulsion. However, little attention has been paid to date to advance the understanding of their dynamic characteristics (natural frequencies, mode shapes and damping) during running. The evaluation of such parameters is now urgently required, as the use of energy-storing-and-returning feet is now being investigated through legal and justice systems to determine participation of amputee athletes using them at the Olympic Games. This paper presents a study of the dynamic characteristics of two commercially available Elite Blade composite feet (solid and split foot). A full modal analysis of the feet was conducted with varying masses attached to them, representing different body masses. The study showed that natural frequencies close to typical running step frequency can be achieved with simple control of the mass or stiffness. It was concluded that further study of the dynamic characteristics could result in a significant change in the design, development and the attitude towards the use of composite prosthetic feet. This initial study has highlighted the key questions that need to be answered to fully understand the dynamic characteristics and inform designers on how to tune a foot to match an amputee’s gait and body condition.

Sprinting with an amputation: Some race-based lower-limb step observations

Background: T44 sprinting with an amputation is still in a state of relative infancy. Future scope for athletic training and prosthetic limb development may be assisted with a better understanding of information derived from T44 athletes when under race-based conditions. Objectives: To investigate the behaviour of step count and step frequency when under competitive conditions. Study design: The study comprises two elements: (1) a video-based analysis of race-based limb-to-limb symmetry and (2) a video-based analysis of race-based step count. Methods: Video analysis of several major events from 1996–2012 are assessed for step count and step limb-to-limb symmetry characteristics. Results: The video analysis highlights limb-to-limb imbalances greater than those indicated in the previous literature. A low step count is determined to be desirable for success in the 100-m event. Conclusion: Future analysis of athletes with a lower-limb amputation would be worthwhile when placed under race-based conditions as the limb-to-limb behaviour is more exaggerated than those seen in typical studies held within a laboratory setting. The within-event behaviour of step counts requires further investigation to establish where these take place or whether it is a cumulative step length issue. Clinical relevance This article increases the understanding of the race-based behaviour of amputee athletes and provides more information to contribute to any discussions on the performance of lower-limb prostheses.

An Investigation Into the Measurement and Prediction of Mechanical Stiffness of Lower Limb Prostheses Used for Running

Two energy return prosthesis are subjected to three different statically applied loading methods. This initial study proposes that statically applied loading to a sport prosthesis using several controlled methods were statistically robust enough to derive a mechanical stiffness value. However, any predicted stiffness is drawn into question when allowing any movement of the distal end. This uncertainty will make any evaluation or prescription of lower limb prosthesis technology based upon their stiffness incorrect. In addition, the peak calculated stiffness at the expected bodyweight induced ground impact load of a runner is judged the most representative assessment method. This study attempts to build on previous research advocating the need to monitor the performance of prosthesis lower limb technology in disability sport.

The dynamic elastic response to impulse synchronisation of composite prosthetic energy storing and returning feet

In this research, it is proven that perfect synchronisation between the input impulse (human effort) and the ground reaction impulse/impact can result in a phenomenon called the dynamic elastic response to impulse synchronisation with favourable consequences to the behaviour of the energy storing and returning foot. An energy storing and returning composite prosthetic foot was first used in elite competition at the 1988 Paralympic Games. Since its introduction, the prostheses have proven to be a source of controversy. In 2008, it was concluded that the athletes who use such technology when running are in an advantageous position when compared to able-bodied athletes. However, these findings have since been disputed. There still remain unanswered questions regarding the level of contribution of energy storing and returning feet in the performance of amputee athletes. A series of investigations have previously been conducted to study the dynamic characteristics of a number of energy storing and returning composite prosthetic feet. It was found that if a sinusoidal input impulse, with a frequency close to one of the energy storing and returning feet’s natural frequencies, could be applied, it can make the energy storing and returning foot susceptible to resonance, which, in the case of bending mode, if sustained can lead to a gain in height or increased velocity.