Dual phase versus TRIP strip steels: comparison of dynamic properties for automotive crash performance

Abstract

The need to simultaneously reduce vehicle emissions and increase the safety of passengers is encouraging the automotive industry to incorporate new technologies and materials into today's vehicles. To remain competitive, the steel industry has developed steel grades with increased energy absorbing properties allowing down gauging of body in white components to address the competition from alternative materials such as aluminium alloys and composites. Two of the more important developments are the introduction of dual phase (DP) and transformation induced plasticity (TRIP) grades for the automotive industry. These grades offer superior strength/formability and work hardening properties compared to conventional high strength grades of similar tensile strength. Utilising thinner gauge components with increased energy absorbing properties would permit addressing the mass/safety issues by the automotive industry. This paper relates the crash performance of a range of both commercial and experimental DP and TRIP grades. Dynamic tensile testing was performed at low and very high strain rates within the range of 0·001–200 s^?1, to allow an extensive analysis of the effect of strain rate on the material properties. Crash testing was also performed on closed top hat sections at low, medium and high strain rates and the results compared to the dynamically tested tensile specimens. This study helped clarify the enhanced performance offered by high strength DP and TRIP strip steel grades during dynamic tensile testing and impact loading conditions. This advantageous behaviour is attributed to the favourable microconstituents present in these novel grades and their deformation characteristics. This paper concentrates only on the crash properties measured from dynamic tensile tests. The microstructural analysis is presented in a separate publication.     

Investigation of quenching effect on mechanical property and abrasive wear behaviour of high boron cast steel

Abstract

The effect of quenching temperature from 900 to 1050°C on the microstructures, mechanical properties and abrasion resistance of modified high born cast steel containing 0·3 wt-%C and 3·0 wt-%B was studied by optical microscopy, scanning electron microscopy, X-ray diffraction analysis, tensile tester, impact tester, hardness tester and abrasion tester. Quenching at 900°C resulted in structures containing a small amount of pearlite. The existence of pearlite led to poor hardness and wear resistance of modified high born cast steel. Quenching at temperatures between 900 and 950°C resulted in the decrease in pearlite and the increase in hardness and abrasion resistance in comparison with 900°C quenching. The metallic matrix all transformed into the martensite quenching at 1000°C; the modified high born cast steel had high hardness, tensile strength, impact toughness and excellent abrasion resistance. The hardness, tensile strength and impact toughness of modified high born cast steel had no obvious change quenching over 1000°C. The increase in quenching temperature also led to the transformation of boride from continuous shape to isolated shape and promoted the coarsening of boride.     

Mechanical safety analysis for high burn-up spent fuel assemblies under accident transport conditions

Abstract

Transport packages for spent fuel have to meet the requirements concerning containment, shielding and criticality as specified in the International Atomic Energy Agency regulations for different transport conditions. Physical state of spent fuel and fuel rod cladding as well as geometric configuration of fuel assemblies are, among others, important inputs for the evaluation of correspondent package capabilities under these conditions. The kind, accuracy and completeness of such information depend upon purpose of the specific problem. In this paper, the mechanical behaviour of spent fuel assemblies under accident conditions of transport will be analysed with regard to assumptions to be used in the criticality safety analysis. In particular the potential rearrangement of the fissile content within the package cavity, including the amount of the fuel released from broken rods has to be properly considered in these assumptions. In view of the complexity of interactions between the fuel rods of each fuel assembly among themselves as well as between fuel assemblies, basket, and cask body or cask lid, the exact mechanical analysis of such phenomena under drop test conditions is nearly impossible. The application of sophisticated numerical models requires extensive experimental data for model verification, which are in general not available. The gaps in information concerning the material properties of cladding and pellets, especially for the high burn-up fuel, make the analysis more complicated additionally. In this context a simplified analytical methodology for conservative estimation of fuel rod failures and spent fuel release is described. This methodology is based on experiences of BAM acting as the responsible German authority within safety assessment of packages for transport of spent fuel.     

Transport of radioactive material in Bangladesh: a regulatory perspective

Abstract

Radioactive material is transported in Bangladesh in various types of packages and by different modes of transport. The transport of radioactive materials involves a risk both for the workers and members of the public. The safe transport of radioactive material is ensured in Bangladesh by compliance with Nuclear Safety and Radiation Control (NSRC) Act-93 and NSRC Rules-97. The Bangladesh Atomic Energy Commission is the competent authority for the enforcement of the NSRC act and rules. The competent authority has established regulatory control at each stage to ensure radiation safety to transport workers, members of the general public and the environment. An overview is presented of the activities related to the transport of radioactive material in Bangladesh. In particular, the applicable legislation, the scope of authority and the regulatory functions of the competent authority are discussed. The categories of radioactive materials transported and the packaging requirements for the safe transport of these radioactive materials are also described.     

Effects of process conditions on mixing between molten iron and slag in smelting reduction vessel via water model study

Abstract

The present study has been conducted to investigate the effects of operating conditions, which include gas flowrate, tuyere size, tuyere number, and height of iron phase, on the extent of mixing between molten iron and molten slag in the direct iron ore smelting reduction process. A transparent acrylic water model, 30% of the size of the actual smelter, was constructed to study the mass transfer phenomena. In the water model, water and spindle oil were used to simulate molten iron and molten slag, respectively, while air was used to replace the bottom blown nitrogen gas. In addition, thymol (C₁₀H₁₄O₆) was used as a tracer material in the water model, added to the water at the beginning of the experiment. As mixing between water and spindle oil proceeded owing to stirring by the bottom blown gas, the concentration of thymol in the water decreased and that in the spindle oil increased. Water samples were taken from the bottom and 12 cm above the bottom of the water model at various operating times. Concentrations of thymol were then measured using a diode array ultraviolet visible spectrophotometer. By analysing the concentration data, the mass transfer rate k_wA, which is a direct index for evaluating the mixing efficiency, could be derived. The process conditions under investigation included 40-500 L min^-1 gas flowrate, 0·3^-1 cm tuyere size, four or five tuyeres, and 20-30 cm height of the water phase. The test results indicate that when the gas flowrate increases, the value of k_wA increases, which indicates better mixing between oil and water phases. However, as the gas flowrate approaches 40 L min^-1, the improvement becomes less obvious. The smaller tuyere gives better mixing, and the design of five tuyeres results in better mixing compared with four tuyeres when they are blown with the same total gas flowrate. However, mixing efficiency decreases with increased height of the water phase. Also, as the gas flowrate of bottom blowing approaches 40 L min^-1, gas blowing from the top has little effect on the mixing behaviour in the liquid bath. For a four tuyere system, the process conditions of height of oil phase 5 cm, height of water phase 25 cm, diameter of tuyere 0·75 cm, and gas flowrate for each tuyere 40 L min^-1, appear to be the optimal design.     

The Criteria for the Transitions Between the Various Oxidation Modes of Binary Solid-Solution Alloys Forming Immiscible Oxides at High Oxidant Pressures

The possible high-temperature corrosion modes ofbinary solid-solution alloys forming two immisciblecompounds by a single oxidant include (1) the exclusivegrowth of external scales of the most-noble component, which may or may not be associated with theinternal oxidation of the most-reactive component, (2)the formation of composite external scales containing amixture of the two compounds, or finally (3) the exclusive growth of the most-stable compound asan external scale. The conditions for the stability ofeach scale structure depend on a number of thermodynamicand kinetics parameters, whose effects are examined quantitatively in this paper. Theconditions for the stability of the various structuresand the criteria for the transitions among them are alsoexamined. The maximum number of possible scale structures is four, but it can reduce to threeand, in some cases, only to two. In particular, theinternal oxidation of the most-reactive component maynot occur if the stabilities of the two oxides are not sufficiently different from eachother.     

Hydrogen effusion from high strength weld metal

Abstract

Constant heating rate hydrogen thermal analyses were carried out for weld metals with tensile strengths in the range 490–1000 MPa. It was found that the hydrogen diffusion rate in the highest strength weld metal is lower by a factor of five than that in a lower strength variant. The hydrogen diffusion behaviour varied greatly between weld metal and wrought steel. Finite difference analyses indicated that this difference can be attributed to the changes in the interaction energy between a trap site and hydrogen. Using the analysis it was possible to determine apparent diffusion rates at temperatures from 20 to 300°C and explain satisfactorily the effect of plastic deformation on hydrogen diffusion in a steel.     

Biomass firing: Danish experiences

Abstract

Denmark has a long-standing objective to reduce carbon dioxide emissions through increased use of biomass for power generation. The chosen biomass, straw, posed significant new challenges for materials and combustion technology, and has also required development of supply chain management. An interdisciplinary approach, involving research organisations and companies from several sectors of industry, has been developed to overcome these requirements. Key achievements of this research and development programme and ongoing targets are reviewed.     

Effect of shrinkage constraint on damage of C/SiC composites during thermal cycles in oxidising atmosphere

Abstract

Thermal cycling response of a three-dimensional C/SiC composite subjected to a unidirectional shrinkage constraint in wet oxygen was investigated. Constraint stress generated on both ends of the composite specimens during thermal cycles is shown to decrease upon heating and increase with cooling. Nevertheless, the peaks of the constraint stress gradually reduced from the initial 41 MPa to the final constant value of 9·8 MPa after 20 cycles. Residual mechanical properties and microstructure characterisation suggest that the cycled composites suffer a little mechanical degradation and the shrinkage constraint is of advantage to oxidation resistance of the materials during thermal cycles.     

Recycling of WC–Co from scrap materials

Abstract

WC-Co scrap generated by the cutting tool industries was electrochemically broken down to cobalt, which was deposited at the cathode and a mixture of tungsten oxide and tungstic acid was collected at the anode with an overall recovery efficiency of about 90%. The tungsten oxide/tungstic acid was reduced to produce nanostructural tungsten powders, which were subsequently carburised and chemically coated with cobalt to produce WC-Co powders. The powders synthesised were characterised for purity and size.The WC-Co powders, thus obtained were consolidated to near theoretical densities using a novel plasma pressure compaction (P²C) technique. The microhardness of the consolidated sample was measured to be 2200 HV, which is 20% higher than the reported literature values.