Assessment of bond interface in impact spot welding

Results of an investigation on weld interfaces of impact-welded dissimilar metal combinations are presented. Polymeric projectiles of various nose shapes are utilized at an average impact speed of 750 m/s. It is found that welded interfaces generally comprise wavy and plane zones. Areas adjacent to waves contain hardened and plastically deformed regions. Quantitative data is presented on the composition of copper/brass interfaces. Results of microhardness measurements on copper/brass, titanium/brass and zirconium/brass weld interfaces are provided. Measurements on the local plastic thinning of the flyer plate (FP) are furnished. Effects of standoff distance (SD) and FP thickness on interface characteristics are investigated.     

Studies on the Coefficient of Friction During the Oblique Impact of a Hard Sphere Against a Ductile Solid Target

Following the original approach of Bowden and Tabor and introducing state variables, an effective friction coefficient μe for solid particle erosion is defined as a combination of shearing term and ploughing term. In the case of continuous sliding, based on considering the interaction between asperities under certain condition, it is indicated that during the oblique impact of a hardened steel sphere against a mild steel target, a possible value of μc is 0.05, which was chosen in all of the calculations by Hutchings for consistency with both experiments and calculations. In the case of continuous ploughing, it is shown that the value of μc is a function of the impact process and the initial impact angle and is greater than 0.05 on an average for Hutchings‘ e xperiments. It is suggested that the variation of sliding, rolling and ploughing state at each instant in the impact process makes “the coefficient of friction“ equal to 0.05 for Hutchings‘ experiments, and in general, makes the effective friction coefficient during particle impact on metal far less than the friction coefficient during simple continuous sliding on an average.     

A note on times to fracture in solid Perspex spheres due to point explosive loading

The internal fracturing of a Perspex sphere due to a localised explosive loading on its surface has been investigated both analytically and experimentally. The locations and times of occurrence of the fractures are predictable from an analysis of stress wave reflection from the free surface based on the methods of geometrical acoustics. High-speed photography was used to measure and note the order in time at which the different fractures occurred.     

Temperature and Rate Effects on GRP Tubes Under Tensile Hoop Loading

A comprehensive study was undertaken to characterise glass fibre reinforced plastic (GRP) tubes at different temperatures and strain rates. The tests were performed on tubes of 25°, 55° and 75° winding angle. The tubes were burst under internal radial pressure with minimum end constraints. Two separate rigs were used, one for the static and the other for the dynamic tests. The tests were carried out at three temperatures; –46°C (low temperature), +20°C (room temperature) and +70°C (high temperature). For each test the internal pressure and the strains in both circumferential and longitudinal directions were recorded on suitable digital processing equipment. For a particular batch of tubes tested at three different temperatures, there is in general a decrease in hoop strength with increasing temperature during quasi-static tests. The use of a non-structural liner during such tests led to an increase in ultimate hoop strain of 55° tubes, especially at high temperature. The corresponding increase in ultimate hoop strain was markedly less in the case of 75° and almost negligible in the case of 25° tubes. Testing the tubes at high strain rates resulted in substantial increases in burst strength and ultimate hoop strain as compared with the quasi-static and low strain rate values. The mode of failure of 75° tube is a catastrophic fibre breakage under all test conditions. The mode of failure of 55° tube is a combination of weeping and fibre failure. The 25° tubes are characterised by matrix failure, which is very severe at high strain rates.     

Plastic collapse of cellular structures comprised of doubly tapered struts

In this paper, micro-structural models are developed to examine the effects of tapered strut morphology on the plastic collapse of cellular structures. The analytical models are for materials that fail by plastic yielding and cover several types of columnar structure (e.g. hexagonal and square honeycombs, and hexagonal and rhombic cellular materials of rod-like columnar structure). The results indicate that the plastic collapse of hexagonal cellular materials is dependent not only on the relative density but also on the strut morphology. The presence of taper in struts can increase or decrease the plastic collapse strength of cellular materials, depending on the strut morphology.     

Dynamic plastic deformation of rings under impulsive load

A study of the plastic response of rings of different materials to different types of dynamic load is presented.

Inertial loading of rings was obtained by allowing heavy lead rings to fall freely on to flat and pointed rigid anvils and impulsive loading was obtained by subjecting stationary lead, copper and aluminium rings to a high-speed bullet or to contact explosives. Heavy mass, low velocity impact loading was obtained by allowing a large tup to freely fall on to the ring. Collision loading was obtained by allowing one ring to fall on to one or two stationary rings.

Two types of approach are employed to analytically investigate the loading of rings. The first is a numerical one which assumes a simple approximate model for the structure of the ring; it reduces the ring to small masses concentrated around the circumference, connected to each other by weightless links possessing the strength properties of the material of the ring. The problem is then reduced to solving the dynamical equations of each mass around the ring with the help of a digital computer. The second is an energy method which utilizes Lagrange's equations for the motion of approximated links within the ring.

Results of each of these approaches are compared with experiments presented in terms of instantaneous deformation obtained from high-speed photographs.     

Effect of Temperature on the Tensile Strength and Failure Modes of Angle Ply CFRP Tubes under Hoop Loading

A comprehensive study was undertaken to characterise carbon fibre reinforced plastic (CFRP) tubes at different temperatures. Quasi-static burst tests were performed on tubes of 25°, 55° and 75° winding angle. The tubes were burst under internal radial pressure with minimum end constraints. An experimental rig and two conditioning tanks were designed and built to test the specimens at three temperatures; -46°C (low temperature), +20°C (room temperature) and +70°C (high temperature). For each test the internal pressure and the strains in both circumferential and longitudinal directions were recorded using a digital processing equipment.For a particular batch of tubes, tested at three different temperatures, a decrease in hoop strength and modulus of the 55° tubes with increasing temperature was recorded; the effect was less pronounced on the properties of 25° and 75° tubes. The use of a non-structural liner during the tests led to higher ultimate strength and strain of 55° tubes but had negligible effects on the behaviour of 75° tubes. The use of a liner in 25° tubes altered the mode of failure, resulting in a very large tube deformation with no noticeable increase in burst pressure. Micrographic analysis was also undertaken to study the failure mechanisms during pressurisation of lined and unlined tubes.     

Simultaneous determination of in-plane shear and transverse moduli of unidirectional composite laminae at different strain rates and temperatures

A semi-empirical method is proposed for the extraction, simultaneously, of the transverse tensile and in-plane shear moduli of unidirectional laminae, at various strain rates and temperatures, from tests on symmetric and balanced ±65 ° angle-ply composite laminates. The extraction method is applied to data obtained from tests on Kevlar-49/epoxy and carbon/ epoxy filament-wound tubes which were subjected to internal pressure loading at three key temperatures of −45, 20 and 70 °C at different strain rates of up to 80/s. The combined effect of strain rate and temperature on these extracted properties is studied by applying strain rate temperature equivalence principles. It is found that the variation of the mechanical properties of the two materials with strain rate and temperature can be adequately described by semi-empirical equations similar to the Arrhenius and Williams-Landel-Ferry relationships, usually used for homogeneous solids.     

The bulging of a superplastic sheet from a square die

Superplastic zinc aluminium eutectoid alloy sheet blanks were bulged from a square die using pneumatic pressure. Methods of describing the bulge centre-line and diagonal profiles are proposed and the predicted profiles are in good agreement with the experimental profiles. “Boxes” of various heights and of various degrees of deformation were formed and their associated strain distributions measured. If the width: height ratio is greater than 1 : 1 the position of maximum strain and, therefore, the most likely location of failure occurs at the corners away from the clamped edge. If the top of the bulge was unrestricted failure occurred at the apex. A limit on the width : height ratio of 2 : 1 is necessary for reasonable strength after cooling and if the forming pressure is less than 20 lbf/in² failure due to excessive corner thinning is avoided.     

Author Index

Authors Index

Author Index