Effect of quasi-static prestrain on the formability of dual phase steels in electrohydraulic forming

Dual phase steels derive their name from their microstructure, which consists of islands of martensite surrounded by a ferrite matrix. These steels are increasingly being used in automobile structures in order to reduce weight, improve fuel economy, and maintain crash safety performance. The higher strength grades of dual phase steels, such as DP780 and DP980, often present significant formability challenges in sheet stamping operations, and therefore any technologies which could alleviate these issues would be of significant value to the automotive industry. Electrohydraulic forming (EHF) is based upon the electro-hydraulic effect: a complex phenomenon related to the discharge of high voltage electrical current through a liquid. In EHF, electrical energy is stored in a bank of capacitors and is converted into the kinetic energy needed to form sheet metal by rapidly discharging that energy across a pair of electrodes submerged in a fluid. During such a discharge, a high pressure, high temperature plasma channel is created between the tips of the electrodes. The resulting shockwave in the liquid, initiated by the expansion of the plasma channel, is propagated toward the blank at the acoustic velocity of the fluid, and the mass and momentum of the water in the shock wave accelerates the sheet metal blank toward the die. The objective of this paper is to report the results of formability testing of dual phase steels under three basic conditions: (1) conventional limiting dome height (LDH) testing; (2) starting with a flat blank and using one pulse of EHF to fill the desired die geometry; and (3) starting with a quasi-static preforming step to partially fill the die cavity and then using one pulse of EHF to fill the remaining area of the die cavity. A hybrid process which combines sheet hydroforming (HF) and EHF as described herein has the potential to reduce the cycle time of the EHF process by replacing the initial EHF forming increments with one quasi-static preforming step. Additionally, a numerical model was developed and employed in order to better understand the sheet deformation process within EHF. The numerical model consists of four distinct models that are integrated into one: (1) an electrical model of the discharge channel, (2) a model of the plasma, (3) a model of the liquid as a pressure-transmitting medium, and (4) a deformable sheet metal blank in contact with a rigid die. Significant improvements in formability were confirmed experimentally for DP780 and DP980 by forming into conical and v-shape dies using EHF from a flat sheet and by using EHF combined with a quasi-static preforming step. Numerical modeling showed that the peak strain rates occurring in both single-pulse EHF the hybrid HF-EHF process are approximately 17,000 units per second.     

Prerequisites for learning from accident investigations – A cross-country comparison of national accident investigation boards

In this paper railway accident investigation reports issued by the national accident investigation boards in three Scandinavian countries during a 2-year period have been systematically studied. Content analysis of attributed causes in these reports reveals a considerable emphasis on physical processes, actor activities and equipment (the microlevel). Much less attention is paid to organisational factors (the mesolevel) and conditions related to regulators, associations and government (the macrolevel). This means that lessons will primarily be learned about aspects at the lower of these levels. Interviews show that the factors emphasised in investigation reports typically reflect the competences and experiences of the investigators, i.e. they are inclined to focus on areas of their own expertise. Since failures at the microlevel in many cases merely are symptoms of trouble at higher levels, it is argued that competence among investigators that supplements entirely technical or operational backgrounds are necessary for enabling deeper understanding of the factors leading to accidents. One possible way for achieving this is the creation of multi-modal investigation boards that provide a number of potential advantages, such as increased access to specialist competences that are shared between different sectors. Although a multi-modal approach to some degree has been adopted in all three countries, interviews reveal that these positive effects do not emerge automatically. It can therefore be concluded that multi-modal investigation boards offer a number of possible advantages, but only when these synergies are fully exploited can they provide a potential for more effective learning from accidents.     

Effects of abiotic factors on growth and chemical defenses in cultivated clones of <Emphasis Type="Italic">Laurencia dendroidea</Emphasis> J. Agardh (Ceramiales,Rhodophyta)

Laurencia dendroidea shows high inter- and intrapopulation variability in the amount of the sesquiterpene elatol, caused by genetic variation as well as environmental factors. To test the independent effect of physical and nutritional conditions, the growth and the levels of elatol in L. dendroidea clones were evaluated under different conditions of temperature, salinity, irradiance, and culture medium in the laboratory. Growth of L. dendroidea was clearly affected by all these factors, but elatol levels were influenced only by temperature and salinity. Better conditions for growth did not produce a similar effect on elatol production in L. dendroidea, contradicting the carbon/nutrient balance and growth/differentiation balance models. On the contrary, severe conditions of temperature and salinity promoted a decrease in elatol levels, as predicted by the environmental stress model. Our results using clones indicated that abiotic factors clearly take part in fostering chemical variations observed in natural populations, in addition to genetic factors, and can promote differential susceptibility of plant specimens to natural enemies.     

A new approach of ecologically based life cycle assessment for biological wastewater treatments focused on energy recovery goals

Environmental Science and Pollution Research - The energy potential of high-organic loaded agro-industrial effluents receiving biological treatment is often neglected, particularly in emergent...     

Bridging the legitimacy gap—translating theory into practical signposts for legitimate flood risk governance

Legitimacy is widely regarded as a founding principle of ‘good’ and effective governance, yet despite intense academic debate and policy discourse, the concept remains conceptually confusing and poorly articulated in practice. To bridge this gap, this research performed an interpretive thematic analysis of academic scholarship across public administration, public policy, law, political science, and geography. Four core themes were identified in relation to representative deliberation, procedural and distributive equity and justice, and socio-political acceptability, with numerous sub-themes therein. In an attempt to clarify conceptual confusion, this paper grounds these theoretical debates in the context of flood risk governance where numerous legitimacy dilemmas exist. A number of questions are presented as conceptual ‘signposts’ to encourage reflexive governance in the future. Thus, more broadly, we assert the importance of bringing legitimacy to the forefront of contemporary flood risk governance discourse and practice, moving beyond the realm of academic reflection.