Axial crushing of wood-filled square metal tubes

The behaviour of thin tubes made of sheet metal and not so thin extruded tubes filled with wood and subjected to axial crushing is studied. Experiments show that the mode of elastic buckling is changed by the presence of the wood filler. The plastic crushing of thin tubes resulted in Euler-type buckling, while a considerable enhancement in the load carrying capacity and energy absorption was seen in the case of thicker walled tubes which were examined both under quasi-static and dynamic loading conditions. A new idealized deformation mechanism for the progressive crushing of the wood-filled tube is suggested and analysed. The results obtained for the mean loads agree reasonably with experimental observations. An alternative method employed to predict the mean crushing load of empty tubes and using a thickness that provides an equivalent stiffness to that of a filled tube is also seen to produce reasonable agreement with the experiment.     

Axial crushing of square tubes

The mechanics of the large deformation of a square tube under axial load is discussed. Theoretical results are substantiated by experimental results. The elastic buckling load is predicted by assuming the tube to be comprised of four plates simply supported at their edges. The highest load the tube can sustain is predicted by allowing for the development of plasticity near the corners. The mean crushing load is predicted from an incremental plasticity analysis which allows for travelling plastic hinges. Comparison with circular tube behaviour is considered and an attempt to explain some of the peculiarities is made.     

Strength and Failure Modes of Hoop Wound CFRP Tubes Under Compressive High Rates of Loading

A study was undertaken to investigate the response of hoop wound carbon fibre reinforced plastic (CFRP) tubes to dynamic compressive loading at strain rates in the range of 5–200/sec. An experimental rig was designed and built to test short tubular specimens under external radial pressure with minimum end constraints. The load was applied by detonating a small explosive charge inside a water filled, steel, cylindrical chamber enclosing the test specimen. For each test the external pressure and the strains, in both circumferential and longitudinal directions, were recorded on suitable digital processing equipment. Two distinct modes of failure were identified; material and structural (buckling). The mode of failure was dependent on the rate of loading and the tube diameter/thickness ratio. For 100 mm diameter tubes with diameter/thickness=40, buckling failure dominated at strain rates below 10/s. However, at higher strain rates, material failure and a considerable enhancement in burst strength was observed. For 100 mm diameter tubes, with diameter/thickness=80, a buckling mode of failure was in evidence in all the tests, irrespective of the rate of loading.R. Ahmad: Presently at School of Mechanical Engineering, University Sains Malaysia, Pulau Pinang, Malaysia.     

Residual Stress Assessment in Thin Angle Ply Tubes

This preliminary study aims to investigate the residual stresses developed in hot cured thin-walled angle-ply filament wound tubes made of E-glass/epoxy, Kevlar/epoxy and carbon/epoxy materials. The residual stresses were estimated from change in geometry of these tubes when axially slitted at ambient temperature. Three basic deformation modes; namely opening up, closing-in and twisting, were observed and these depended on the winding angle, material and wall thickness. The residual stresses were also determined from hoop and axial strain gauges mounted on both the inner and outer surfaces at various locations around the tube. The stresses were compared with theoretical prediction based upon a linear thermo-elastic analysis. Both the predicted and measured values were found to increase with increasing hoop stiffness but there was a large discrepancy between the predicted and measured data, reaching a factor of 5 for the thinnest case. When compared with predicted failure stresses, the experimentally determined stresses were some 15% of the computed compressive strength.     

Fracture in solid spheres and circular disks due to a “point” explosive impulse on the surface

The results of an experimental study of the fracture of solid spheres and circular disks due to the explosion of a detonator on the surface are presented and a simple analysis is developed which reasonably explains the nature of the characteristic fracture patterns encountered.     

Experimental investigation of deformation and jetting during impact spot welding

A test setup is described for investigating flyer plate deformation during impact spot welding. High speed photography is used to study the dynamics of bulge formation, spark growth, and projectile illumination during primary and secondary impact of flat-ended projectiles. It is suggested that fragmentation of the spark is due to inter-metallic jetting. Measurements on collision angle β and collision front velocity are reported for several metal plate combinations.     

Hydrogen production via decomposition of methane over activated carbons as catalysts: Full factorial design

The thermo-catalytic decomposition of methane is proposed as an alternative for producing hydrogen without CO₂ emissions. The present study was divided into three parts. First, a screening study of the rate of methane decomposition (RCH₄)$\left(R_{{\text{CH}}_4}\right)$ was performed using two types of activated carbons as catalysts with progressive time of methane decomposition at four different temperatures. The catalysts differed in textural properties. A full factorial design consisting of 20 experimental points for each catalyst was applied in the second part. Quadratic RCH₄$R_{{\text{CH}}_4}$ models as functions of the relative time of catalyst deactivation and decomposition temperature were developed by regression analysis of variance. The results of the RCH₄$R_{{\text{CH}}_4}$ models showed that the relative time had twice as much influence as temperature. Finally, a general RCH₄$R_{{\text{CH}}_4}$ model was then developed representing both catalysts regardless of their textural properties. All the empirical models were consistent with experimental results and were adequate for designing the methane decomposition process.