Zhongwei Guan

The low-velocity impact response of fiber-metal laminates

The low-velocity impact response of a series of glass fiber reinforced epoxy/aluminum alloy fiber metal laminates has been investigated. The influence of varying target thickness, plate diameter, and impactor radius has been studied and the results compared to those offered by plain composite samples. After testing, many samples were sectioned in order to highlight the failure modes under low-velocity impact loading. The FMLs absorbed significant energy in plastic deformation, tearing the metal layers and fiber fracture, and offered a superior impact resistance to the plain composite on which the FMLs were based. The perforation data were normalized by the areal density of the target and the superiority of the metal—composite hybrids remained in evidence. Increasing the target size, the plate thickness, and the indentor diameter resulted in an increase in the energy required to perforate the target. In contrast, impacting the square panels at the corner or along the edge of the target did not have a significant effect on the perforation response of the structures.

Hollow steel dowels — a new application in semi-rigid timber connections

Dowel type fasteners used in timber joints are traditionally of solid cross section. The rigidity of those with a larger diameter increases the chances of brittle failure in the timber components. Hollow fasteners of variable wall thickness, whilst maintaining the required timber performance, offer variable fastener rigidity and the likelihood of enhanced joint ductility. This paper describes a finite element based model which was validated against the results of a series of tests on single hollow steel dowel timber joints and then used to conduct a parametric study of the effect of fastener wall thickness on joint performance.

Experimental study on impact-initiated characters of multifunctional energetic structural materials

Multifunctional energetic structural materials (MESMs) are a new class of energetic materials, which release energy due to exothermic chemical reactions initiated under shock loading conditions. In order to analyze the impact-initiated process of MESMs, a quasi-sealed test chamber, which was originally developed by Ames [“Vented chamber calorimetry for impact-initiated energetic materials,” in AIAA (American Institute of Aeronautics and Astronautics, 2005), p. 279], is used to study on shock-induced chemical reaction characters at various impact velocities. The impact initiated experiments are involving two typical MESMs, Al/PTFE (polytetrafluoroethylene), W/Zr and inert 2024 Al fragment. The video frames recorded from reactive and inert material impact events have shown the process of late-time after burn phenomena. The total pressure and shock wave reflection at the wall of the test chamber are measured using high frequency gauges. The quasi-pressures inside the test chamber, which is fitting from the t...

The response of polymeric composite structures to air-blast loading: a state-of-the-art

Abstract Composite materials are finding use in an increasing number of structural applications as a result of their high specific strength, high specific stiffness, thermal resistance and the potential for tailoring of properties to suit specific applications. Fibre-reinforced composites, foam core sandwich panels and fibre-metal laminates (FMLs) are examples of composite materials that are employed in high-performance engineering applications, for example in yachts, passenger aircraft, racing cars and sports equipment. Explosive loading is a potential threat to many of these structures, and therefore an improved understanding of the response of such systems to air-blast loading is important. This paper reviews recent experimental and numerical work on the response of composite materials, sandwich structures and hybrid materials to air-blast loading. Commonly employed experimental techniques used to simulate air-blast loading conditions are described, along with the results from recent experiments on plain composite laminates, polymeric sandwich panels and FMLs. The influence of loading distribution, materials and test geometry on the failure of composites is discussed. The latter part of paper discusses numerical modelling considerations and reports methods and results from recent numerical modelling work on the blast loading of composites.

The quasi-static and blast response of steel lattice structures

Lattice structures based on two simple architectures have been manufactured from 316L stainless steel using the selective laser melting process. The compressive properties of structures based on a body-centered cubic (BCC) and a similar structure with vertical pillars (BCC-Z) were initially investigated at quasi-static rates of strain. Blast tests were subsequently performed on the lattice structures as well as on lattice sandwich structures with CFRP skins. When subjected to quasi-static compression loading, the BCC structure exhibited a progressive mode of failure, whereas the BCC-Z lattice deformed in a buckling-dominated mode of collapse. The blast response of the lattice cubes exhibited a linear dependency on the applied impulse up to the threshold for material densification. Relationships between the blast resistance and both the yield stress and energy absorption characteristics of the lattices have been established and an examination of the failed samples indicated that the collapse modes were similar in both the quasi-static and blast-loaded samples. Finally, the failure modes observed in the blast-loaded sandwich panels were investigated and found to be similar to those observed in the lattice blocks.

Finite element modelling of OSB webbed timber I-beams with interactions between openings

Experiments were conducted on beams with openings spaced at different intervals along the web. It was observed that the OSB fractured from tension zones around an opening, with cracks developing diagonally towards the beam flanges. A beam would collapse when the cracks reached the flanges. Interactions between openings further reduced the load carrying capability of a beam and changed its failure pattern. Using ABAQUS, Finite element models were developed to simulate beam behaviour. Material nonlinearity, fracturing of OSB, crack propagation and beam failure were dealt with by a user subroutine. Good correlation was obtained between test and analytical results. Critical distances between openings were also investigated.

The structural performance of thin-walled polyethylene pipe linings for the renovation of water mains

Abstract Renovation of deteriorating metal pipe with a close-fitting polyethylene lining is now standard practice in the U.K. water industry. Usually a full-thickness pressure pipe is used for the lining. However, here it is argued that capacity to span relatively small gaps and corrosion voids is often the major structural requirement of the lining. Under these circumstances an appropriate thin-walled lining (i.e. thinner than a full-pressure pipe) will yield both cost savings and a larger renovated pipe bore. Performance criteria for these linings are then obtained from a three-phase programme of research: firstly the creep performance of medium density polyethylene (MDPE) under the stress states of interest is determined; secondly a series of short-term tests to failure of representative systems is undertaken; finally a finite element model is generated which is initially calibrated aginst the short-term test results and then used to predict 50 year creep lives. These predictions suggest that at least a two-thirds reduction in material costs on normal practice is often achievable.

Development of thermal models of footwear using finite element analysis.

Thermal comfort is increasingly becoming a crucial factor to be considered in footwear design. The climate inside a shoe is controlled by thermal and moisture conditions and is crucial to attain comfort. Research undertaken has shown that thermal conditions play a dominant role in shoe climate. Development of thermal models that are capable of predicting in-shoe temperature distributions is an effective way forward to undertake extensive parametric studies to assist optimized design. In this paper, two-dimensional and three-dimensional thermal models of in-shoe climate were developed using finite element analysis through commercial code Abaqus. The thermal material properties of the upper shoe, sole, and air were considered. Dry heat flux from the foot was calculated on the basis of typical blood flow in the arteries on the foot. Using the thermal models developed, in-shoe temperatures were predicted to cover various locations for controlled ambient temperatures of 15, 25, and 35 °C respectively. The predicted temperatures were compared with multipoint measured temperatures through microsensor technology. Reasonably good correlation was obtained, with averaged errors of 6, 2, and 1.5 per cent, based on the averaged in-shoe temperature for the above three ambient temperatures. The models can be further used to help design shoes with optimized thermal comfort.

Thermochemical modeling of temperature controlled shock-induced chemical reactions in multifunctional energetic structural materials under shock compression

Multifunctional energetic structural materials (MESMs) are a new class of energetic materials which release energy due to exothermic chemical reactions initiated under shock loading conditions. In order to analyze shock-induced chemical reactions (SICR) for MESMs, theoretical models have been developed to calculate the Hugoniot data which include the heat released by shock temperature controlled reactions. The temperature rise of porous materials due to shock compression is first calculated using a constant volume and pressure adjustment. Then the Arrhenius reaction rate and Avrami-Erofeev kinetic models are used to calculate the extent of reaction of MESMs under shock compression. Thermochemical models for shock-induced reactions, in which the reaction efficiency is considered, are given by combining the shock temperature rise with the chemical reaction kinetics. The Hugoniot relations and temperatures are calculated by using the proposed method. The models developed have been validated against the exper...

A cold energy mixture theory for the equation of state in solid and porous metal mixtures

Porous or solid multi-component mixtures are ubiquitous in nature and extensively used as industrial materials such as multifunctional energetic structural materials (MESMs), metallic and ceramic powder for shock consolidation, and porous armor materials. In order to analyze the dynamic behavior of a particular solid or porous metal mixture in any given situation, a model is developed to calculate the Hugoniot data for solid or porous mixtures using only static thermodynamic properties of the components. The model applies the cold energy mixture theory to calculate the isotherm of the components to avoid temperature effects on the mixtures. The isobaric contribution from the thermodynamic equation of state is used to describe the porous material Hugoniot. Dynamic shock responses of solid or porous powder mixtures compacted by shock waves have been analyzed based on the mixture theory and Hugoniot for porous materials. The model is tested on both single-component porous materials such as aluminum 2024, cop...