Application of Two Independent Measurement Techniques for Determination of Ductile Crack Growth Initiation

Charpy impact testing of the high strength low-alloyed steel has been performed by simultaneously recording two independent signals. The magnetic emission (ME) and potential drop (PD) techniques were used to determine critical crack initiation properties on standard three-point pre-cracked bending specimens at room temperature. Both signals (ME and PD) were recorded by digital oscilloscope with a high sampling rate and compared, with the purpose of more precise identification of critical fracture mechanics parameters determining the onset of ductile crack growth. This revised version was published online in July 2006 with corrections to the Cover Date.     

Geometry,mechanical properties and mounting of perforated plates for ballistic application

In this paper, the ballistic resistance of perforated plates made of different types of steel, mounting and geometry was investigated. Different types of steel in various heat treatment conditions were tested. Target mounting was also varied: rigid, oblique and hanging. Furthermore, four different perforated plate geometries were tested: two plate thicknesses and two hole diameters. Their behaviour was tested using impact from firing 12.7 mm M-8 API ammunition at eleven perforated plate samples. These samples were placed by means of a steel frame over a 13 mm RHA plate, at two distances. Damaged area on targets was correlated to ballistic resistance of the whole armour to find the optimal perforated plate. It was found that perforated plates, in optimized case offer a frequent fracture of the penetrating core in up to five parts. This debris is unable to penetrate the basic plate, offering mass effectiveness of the whole armour model of 1.76 and the mass effectiveness of the perforated plate of 5.91.     

Accurate natural convection modelling for magnetic components

An accurate presentation of convection heat transfer in magnetic components is proposed for isothermal surface approach. The presented improved modelling of convection heat transfer includes also the effects of the orientation of the component and the influence of the ambient temperature. The proposed modelling is verified by comparison with experimental data obtained for an experimental box shape. The carried out accurate measurements for four different kinds of surfaces of the experimental model allow a fine-tuning of the improved expression for convection heat transfer coefficient h_c. The derived results can be used in a precise thermal design of magnetic components as well for other electronic equipment.     

Wire fence as applique armour

In this paper, the behaviour of wire fence was investigated for potential as applique armour. The wire fence used was made from commercial high-strength patented wire and the supporting frames were made of mild steel L-profiles. Both patented wire and L-profiles are of-the-shelf materials. The fence was tested by firing 12.7 mm M8 API ammunition at four applique armour models: two of these models use a parallel wire arrangement, with one mounted at a 90° angle from the incoming projectile and the other at 70°; and two of these models use a zig-zag wire arrangement, one mounted at a firm 90° angle and the other is left in a hanging arrangement. Fence damage was correlated with RHA basic plate damage, on both the face and back. Wire fence has considerable potential as an improvised applique armour, except if the projectile impacts near the center of the wire or near the center between two wires. The latter case was successfully overcome by placing the armour model at an angle and by using a zig-zag wire arrangement. The lowest basic RHA plate damage level was found using the hanging armour model. However, from the point of view of ease of attachment, the most convenient was found to be the armour model with the zig-zag wire arrangement fixed at 90° angle from the incoming projectile. SEM fracto graphy revealed that the fracture surface was predominantly ductile, with dimples filled with debris from the incendiary effect of the projectile.     

Static and impact crack properties of a high-strength steel welded joint

In order to gain the benefits of weldable high-strength steels in pressurized equipment applications, satisfactory toughness and crack properties of the welded joint, both in the weld metal and the heat-affected –zone (HAZ), are required. Experimental investigations of toughness and crack resistance parameters through static and impact tests of a high-strength, low-alloy steel (HSLA) with a nominal yield strength of 700 MPa and its welded joint, were performed on Charpy-sized specimens, V-notched and pre-cracked, of the parent metal, weld metal and HAZ. The selected electrode produced slight undermatching and enabled the welded joints to be manufactured without cold cracks. The impact energy and its parts responsible for crack initiation and propagation were determined by toughness evaluation. Crack sensitivity, defined as the ratio of the impact energy for V-notched and for pre-cracked specimens, enabled a comparison of the homogeneous microstructure of the parent metal and the weld metal, and of the heterogeneous microstructure of the heat-affected-zone (HAZ), which indicated a better crack toughness behaviour of the HAZ. The results obtained showed that the toughness and crack resistance of the weld metal were significantly lower than those of the parent metal and the HAZ. The fracture mechanics parameters, J_Ic integral, and plane strain fracture toughness, K_Ic, as well as J resistance curves expressed the degradation less.