Horace Whitworth

Deconstructing Engineering Education Programmes: The DEEP Project to reform the mechanical engineering curriculum

The goal of the Deconstructing Engineering Education Programmes project is to revise the mechanical engineering undergraduate curriculum to make the discipline more able to attract and retain a diverse community of students. The project seeks to reduce and reorder the prerequisite structure linking courses to offer greater flexibility for students. This paper describes the methods used to study the prerequisites and the resulting proposed curriculum revision. The process involved dissecting each course into topics at roughly the level of a line in a syllabus, editing the list of topics, associating prerequisites and successors to each topic and then using a genetic algorithm to produce clusters of topics. The new curriculum, which consists of 12 clusters, each of which could be a full year course, is quite different from the traditional curriculum.

Shear band formation in AISI 4340 steel under dynamic impact loads: Modeling and experiment

In this study, the occurrence of the adiabatic shear bands in AISI 4340 steel under high velocity impact loading was investigated using finite element analysis and experimental tests. The cylindrical specimen subjected to the impact load was divided into different regions separated by nodes using finite element method in ABAQUS environment with boundary conditions specified. The material properties were assumed to be lower in the region where the probability of strain localization is high based on prior experimental results in order to initialize the formation of the adiabatic shear bands. The finite element model was used to determine the maximum flow stress, the strain hardening, the thermal softening, and the time to reach the critical strain for the formation of adiabatic shear bands. Experimental results show that deformed bands were formed at low strain rates and there was a minimum strain rate required for the formation of the transformed band in the alloy and the cracks were initiated and propagated along the transformed bands leading to fragmentation under the impact loading. The susceptibility of the adiabatic shear bands to cracking was markedly influenced by the strain-rates and the initial material microstructure. The simulation results obtained were compared with the experimental results obtained from the AISI 4340 steel under high strain-rate loading in compression using split impact Hopkinson bars. A good agreement between the experimental and simulation results was obtained.

Mechanical Properties of Ultrafine Grain 2519 Aluminum Alloy

The effect of percentage thickness reduction and annealing time on the mechanical properties of cryo-rolled AA 2519 aluminum (Al) alloy were examined. Tensile tests was performed on samples in the longitudinal, transverse and at 45° to the rolling direction. The mechanical properties such as the Yield Strength (YS) and the Ultimate Tensile Strength (UTS) were observed to improve when compared to as-received sample of the 2519 alloy. This is in agreement with the Hall-Petch relationship. The highest variations in these properties were observed in the longitudinal direction, followed by the 45° and the lowest values were obtained in the transverse direction. However, the difference between the mechanical properties in the various directions decreased with an increase in annealing time showing homogeneous distribution of the fine particles.

On Fatigue Strength Reduction Factor: State of the Art

Numerous theoretical models have been developed to predict the fatigue strength reduction factor (also known as fatigue notch factor), an important parameter in fatigue life prediction of notched components. These models include: the classical average stress method, the fracture mechanics method, the stress field intensity method, the strain energy method, and the weakest link method. However, most of these methods do not incorporate explicit sensitivity to materials microstructure. Accordingly, notch sensitivity remains a highly empirical subject in spite of significant advances in microstructure-sensitive modeling. This paper gives a detailed literature review of these methods and addresses their limitations. It also discusses a recently developed probabilistic method for microstructure-sensitive fatigue notch factor. The probabilistic method provides a very strong physical basis for fatigue strength reduction and associated notch sensitivity; thus it can be used to determine the effect of notches on reduction of fatigue resistance in a way that directly incorporates microstructure. The results obtained using the new probabilistic framework and other conventional methods are compared with experimental data for notched components. The probabilistic framework gives better correlation with experimental results for the notch sensitivity and notch size effect than the conventional approaches including the Neuber’s, the Peterson, and the fracture mechanics methods.Copyright

Modeling and Simulation of Adiabatic Shear Bands in AISI 4340 Steel Under Impact Loads

In this study, the effects of microstructure and strain rate on the occurrence and failure of adiabatic shear bands in AISI 4340 steel under high velocity impact loads are investigated using finite element analysis and experimental tests. The shear band generated due to impact load was divided into some set of elements separated by nodes using finite element method in ABAQUS environment with initial and boundary conditions specified. The material properties were assumed to be lower at the second element set in order to initialize the adiabatic shear bands. The strain energy density for each successive node was calculated successively starting from the first element where initial boundary condition, initial strain hardening constant, and stress resistance had been specified. As the load time is increased, its corresponding effect on the localized shear deformation and width of the adiabatic shear band was also determined. The finite element model was used to determine the maximum stress, the strain hardening, the thermal softening, and the time to reach critical strain for formation of adiabatic shear bands. Experimental results show that deformed bands were formed at low strain rates and there was a minimum strain rate required for formation of transformed band in the alloy. The experimental results also show that cracks were initiated and propagated along transformed bands leading to fragmentation under the impact loading. The susceptibility of the adiabatic shear bands to cracking was markedly influenced by strain-rates and the initial material microstructures. The numerical results obtained were compared with the experimental results obtained for the AISI 4340 steel under high strain-rate loading in compression using split impact Hopkinson bars. A good agreement between the experimental and simulation results are also obtained.Copyright

Effect of Friction on Contact Stress Distribution in Pin-Loaded Orthotropic Plates

An analytical solution is presented for determining the stress distribution in pin loaded composite joints using Lekhnitskii’s complex stress function approach. In this analysis, it is assumed that the pin is rigid, no clearance exists between pin and plate, and Coulomb friction is assumed to act throughout the contact region. The analysis also assumes that the contact boundary at the pin-plate interface spans through half of the hole boundary. The boundary conditions at the pin-plate interface are specified in terms of the trigonometric series used to represent the displacement field in the contact zone. Numerical results are presented for stress distribution in (±45°)s and (04°/±45°)s carbon fibers reinforced laminates.Copyright

A New Extreme-Value Probabilistic Framework for Predicting Fatigue Crack Initiation Life of Notched Components

Traditional deterministic methods for predicting the fatigue life of notched components require a number of approximations based on heuristics and phenomenological data rather than solid theoretical underpinning and still yield unsatisfactory and inconsistent results when applied to complex components under service loads. Microstructural inhomogeneities in the materials are still an important issue, but are not explicitly accounted for in the traditional deterministic methods. Recent developments in computational crystal plasticity and microstructure-scale modeling have provided deeper understanding of the complex correlations between properties and structures and further indicate the limitations of conventional fatigue life prediction approaches. These modeling approaches have the potential to substantially reduce the need for costly large scale experimental programs to determine scatter in fatigue, for example. At present, however, there is a lack of simulation-based strategy for considering interactive effects of stress/strain field gradients at the notch-root and microstructure-scale behavior in predicting notch-root fatigue crack initiation. In this paper, the distribution of a shear-based fatigue indicator parameter computed within a well-defined fatigue damage process zone at the notch are used along with a novel probabilistic mesomechanics approach to obtain the probability distribution of fatigue crack initiation of notched components, thus extending fatigue life prediction to explicitly incorporate microstructure sensitivity via probabilistic arguments. The new probabilistic framework presented in this paper takes into account the complete plastic shear strain field around the notch root and also links the variation in the materials microstructure and associated slip activations to observable scatter in fatigue strength of the notched component. The use of such probabilistic approach can be beneficial as it avoids conservatism that may result from the use of deterministic approach for fatigue life prediction.Copyright

Strength Analysis of Composite Pinned Joints

Joining by mechanical fasteners is common practice in the assembly of structures. For advanced composites, attachment by means of bolts or screws becomes more attractive, not only in view of assembly and disassembly, but also because of fabrication simplicity and structural efficiency, Theo De Jong [1]. In the analysis of mechanically fastened joints in orthotropic materials, the prediction of the stress distribution around the fastener hole is of fundamental interest for the prediction of strength. Since joints can lead to premature failure of the structure, joint strength is an important property in any design.