Graham Schleyer

A modelling scheme for predicting the response of elastic–plastic structures to pulse pressure loading

This paper is concerned with the analysis of structural members subjected to dynamic loading arising from an accidental explosion or bomb blast. The thrust of the paper is on approximate techniques for predicting the response of structural members to pulse pressure loading in which elastic deformations have a significant effect. The type of loading is of the kind to cause plastic deformation and large deflections in the members leading, in the extreme case, to uniaxial tensile failure or loss of integrity at the supports. The structural geometry, material behaviour and load intensity and distribution are such that the structure responds as a whole. The approach has been developed primarily for the class of problems in which elastic effects are significant, pulse shape is irregular, boundary conditions are neither fixed nor simply supported and the loading is in the quasi-static to dynamic regime.

Electrorheological and magnetorheological fluids in blast resistant design applications

The performance of electrorheological (ER) and magnetorheological (MR) fluids under impulsively-applied loads is investigated. The ER fluid device, which is operating in the squeeze flow mode, is tested with four different ER fluids, while the MR fluid device is a commercially available shock absorber in which the flow resistance of the fluid is controlled by a small electromagnetic element. Both devices were tested in an experimental rig, capable of providing fast loading that represents the typical loading of an explosive shock in air or the typical loading of a hydrocarbon type explosion. These devices were seen to exhibit sufficient field-induced damping forces when subjected to various mechanical and electrical inputs and hence, they are capable of providing adaptable fixing characteristics for blast resistant and structural members such as blast walls on offshore platforms. In addition, the performance of the ER fluid device under fast loading could be predicted by a theoretical model based on the assumption of a bi-viscous fluid characteristic, and was found to compare very well with that acquired experimentally.

Dynamic response of cylindrical explosive chambers to internal blast loading produced by a concentrated charge

The structural dynamic behaviour of cylindrical explosive chambers to internal blast loading produced by concentrated explosive charges is studied. Special attention is given to the formation and development of dynamic strain growth and the factors which affect it in the dynamic loading of explosive chambers. Theoretical treatment of the strain growth and strain growth factor is given for the first time. It is pointed out that the superposition and interaction of different modes of response with similar frequencies is regarded as the mechanism of strain growth and that the geometry of the chamber is the crucial aspect controlling the degree of strain growth. In the theoretical analysis, the shell equations which consider transverse shear and rotatory inertia are adopted. Two test vessels with length to diameter ratios of 1 and 2, respectively, are used in loading experiments with three different amounts of explosive charge. The experimental data and theoretical computations are compared and show very good agreement, confirming that the method proposed in this paper can be applied to estimate the strength of cylindrical explosive chambers subjected to internal dynamic loading.

Understanding the behaviour of fibre metal laminates subjected to localised blast loading

The modelling particulars of the response of Fibre-Metal Laminates (FML) to localised blast loading are discussed, particularly considering the debonding failure at the composite-metal interface. Attention is paid to the though-thickness transient deformation process in order to interpret the deformation mechanism due to highly localised pressure pulses. The study is based on previously reported experimental results on FML panels comprising different numbers of aluminium alloy layers and different thickness blocks of GFPP material. Good agreement between the experimental results and numerical predictions is demonstrated. A brief comparison between the response of a relatively thin FML panel and a monolithic aluminium alloy plate is presented.

Unusual strain rate sensitive behaviour of AISI 316L austenitic stainless steel

This paper presents the results of quasi-static and dynamic tensile tests on 2, 3 and 4 mm thick 316L austenitic stainless steel. It details the test conditions and discusses the results, particularly focusing on strain rate sensitivity and methods of employing the tensile properties in the finite element package, ABAQUS. The results show that the stainless steel is moderately strain rate sensitive in the region of yield. At the ultimate tensile strength (UTS), some negative strain rate sensitivity was observed, which previous researchers for this grade of steel have not reported. Two main conclusions were drawn, namely (a) the strain rate sensitivity was too complex to be modelled accurately by a constitutive equation such as the Cowper-Symonds relation and (b) the properties of the tested materials could be accurately described by a few (true stress, logarithmic strain) coordinate pairs, as linear strain hardening was observed, for a given strain rate.

Peer tutoring in conceptual design

A peer tutoring scheme has been introduced into the Department of Engineering at the University of Liverpool to help 2nd year undergraduate students tackle conceptual design problems. Conceptual design is an iterative process consisting of a series of generative and evaluative stages, which gradually converge on a preferred conceptual solution. Students are generally less comfortable with the task of generating, evaluating and presenting ideas and this leaves them less able to tackle a conceptual design project without the help and intervention of available teachers or experts. Formally, the students were taught through lectures, coursework and critique sessions. Peer tutors were trained to facilitate group sessions whereby the students were able to discuss ideas, evaluate new concepts, generate solutions and learn to communicate more effectively within a non-threatening environment. The students developed problem-solving skills, became more confident and took more responsibility for their own learning. The peer tutoring process also had a positive effect on the tutors, who felt they had become more responsible and employable, improved their communication and leadership skills and deepened their own understanding of design, as a result of the peer tutoring experience.

A Comparison between Electrorheological and Magnetorheological Fluids Subjected to Impulsive Loads

This paper is concerned with an experimental comparison of the dynamic performance of an Electrorheological and a Magnetorheological fluid when subjected to impulsively applied loads. The ER device was built as a squeeze cell incorporating an ER fluid sandwiched between two electrodes which, during impact, move towards each other, whilst the MR device was a commercially available vibration absorber. Each device was mounted in an experimental rig which was capable of determining the instantaneous responses of the fluids. The transient characteristics of the devices were assessed for various mechanical force levels and, for the ER device, under DC excitation of the fluid in conjunction with a digital controller to provide a constant applied electrical field.

Predicting the effects of blast loading arising from a pressure vessel failure: A review:

Abstract An explosion resulting from a pressure vessel failure, during pressure testing or otherwise, could cause major damage to process plant and surrounding structures, not to mention injury to personnel. Thus, at the design stage or during pressure testing, loading and response data are required for risk assessment purposes and in order to make provision in the event of an incident. This review paper discusses commonly used simplified methods of predicting the effects of blast loading on ductile metallic structural components that could arise for example from the rupture of a gas-pressurized vessel, and is useful for engineers who lack any basic knowledge of blast loads and their effect on structures. It is assumed that the characteristics of the explosion source and blast wave have been previously estimated using, for example, the R3 impact assessment procedure.

On pulse pressure loading of plates with holes

This paper reports the application of an energy solution to a complex problem involving large inelastic deformation in thin, clamped ductile square plates with either square or circular holes under the action of transverse pulse pressure loading. The work is part of a collaborative project to study blast loading of steel plates with penetrations as used for deck plating or bulkheads that may be required to resist loading far in excess of their design limit due to the effects of an accidental explosion. A novel differential pressure loading device was used to impart dynamic loading to 1/8 scaled 0.5 m, 1.1 mm thick, clamped mild steel square plates with a central aperture up to 4% of the plate area. This data was used to validate the energy approach that considers both plastic hinge formation and extensional effects. Accounting for strain rate, scaling and dynamic effects in the tests gave more than acceptable results when compared with final deflections in the tested plates. It is concluded that the energy approach together with small-scale test validation paves the way for a versatile robust design methodology which can be used to advantage for screening purposes and/or early stage conceptual design studies.

Characterisation of Aluminium Matrix Syntactic Foams Under Static and Dynamic Loading

Development of a lightweight, strong and energy-absorbing material that has potential application for the protection of vehicles and occupants against impact and blast, is a difficult challenge facing the materials community. Aluminium matrix syntactic foams will be investigated as a possible core material as part of a multi-layered protection system for military vehicles. Aluminium matrix syntactic foams are composite materials consisting of an aluminium matrix implanted with hollow or porous ceramic particles. This paper investigates the mechanical properties of aluminium matrix syntactic foam with different sizes of ceramic micro-spheres and different grades of aluminium, fabricated by the pressure infiltration method. The static crushing behaviour of the foam was investigated under two test conditions using an Instron 4505 machine. Results are compared and discussed. The dynamic compressive response was investigated using a drop-weight impact test machine. It was found that the particle size of the ceramic micro-spheres and the grade of the aluminium metal have a significant effect on the energy absorption capacity of the material. The compressive strength of the syntactic foam was found to increase with increasing compressive strength of the metal matrix.