A study on the effect of chemical composition on the microstructural characteristics and mechanical performance of DP1000 resistance spot welds

This paper reports on the factors governing the mechanical properties of resistance spot welded hot dip galvanized DP1000 under tensile-shear and cross-tension loading. In particular the effects of chemical composition on the microstructural evolution and mechanical properties of DP1000 resistance spot welds are studied thoroughly, by comparison of a higher and lower carbon alloying approach. It is shown that DP1000 steel with higher carbon content attains a martensitic microstructure in the weld nugget with smaller prior austenite grains and finer block sizes. The intervariant boundary fraction analysis also reveals that DP1000 steel containing lower carbon content shows stronger variant selection as the fraction of variants belonging to the same Bain group is higher for this steel. Intervariant plane distribution also reveals that the most of intervariant boundaries for both steels terminated at or near {011} slip planes. Mechanical testing of the welds reveals that the steel with higher carbon content shows a better mechanical performance in tensile-shear test, whereas the DP steel with a lower carbon content exhibits higher maximum load of cross-tension test. The key factors controlling the mechanical response of resistance spot welds during two different mechanical tests are explored via nanoindentation, slit-milling method combined with digital image correlation and micro-cantilever bending. It is demonstrated that the strength and/or hardness of the weld nugget is the key parameter governing the tensile-shear strength of the spot welds, while the fracture toughness of the weld is the dominant parameter that determines the cross-tension strength

Resistance spot welding of advanced high strength steels:Mechanical properties and failure mechanisms

The safety of passenger cars and lorries is determined significantly by the performance of resistance spot welds (RSW) that keep the components of steel together. Advanced high strength steels (AHSS) are known to be more susceptible to weld failure than conventional mild steels. A key issue encountered in the current development of the AHSS and next-generation automotive steels is the catastrophic failure of the welds, accompanied by considerably reduced strengths and toughness. Problems arise mainly in the cross-tension tests of spot welds in AHSS steels of strength > 800 MPa, where welds are subjected to a mode I type loading. The lowered cross-tension strength and poor failure mode of spot welds form a direct hurdle for a successful implementation of these new advanced steels in the automotive industry. Therefore, improvement of the mechanical performance of AHSS resistance spot welds is of vital importance to ensure the safety and crashworthiness of the cars. The present work aims at identifying the process-structure-property relationship in the RSW of dual phase (DP) steels and third generation AHSS steels. Special attention is paid to the microstructural evolution of the welds as a function of welding scheme and parameters. The effect of the precise welding scheme (i.e. single and double pulse) on the microstructural evolution and mechanical response of DP1000 resistance spot welds were studie

Prevention of Drowning by Community-Based Intervention: Implications for Low- and Middle- Income Countries

Background: Drowning is a serious but neglected health problem in low-and middle-income countries. Objectives: To describe the effectiveness of drowning prevention program on the reduction of drowning mortality rates in rural settings at the north of Iran, and guide its replication elsewhere. Patients and Methods: This interventional design included pre- and post-intervention observations in the rural area of the Caspian Sea coastline without a comparison community. Cross-sectional data were collected at pre- and post-intervention phases. Outcome evaluation was based on a four-year period (March 2005-March 2009) utilizing drowning registry data for the north of Iran. Results: The implementation program increased the rate of membership in an organization responsible for promoting safety in high risk areas near the Caspian Sea. Compared to a WHO standardized population, drowning incidence in rural areas of the study demonstrated a continuous decrease in age-specific drowning rate among the oldest victims with a gradual decline during the implementation. In the study area, the epidemiological aspects of the study population were exposed and contributing factors were highlighted. Conclusions: This study showed that the promotion of passive interventions had a greater effect on drowning rate than that of active interventions

Investigating the Attachment in Urban Residential Environments (Case Study: Tehran Navvab District)

The attachment to a place can be described as a meaningful relationship between person and place, an emotional bond that people consider to be worthwhile as a setting to return. Attachment to a place is an indicator by which one can measure the degree of distinction of that place among people compared to other places. these distinctions are the result of a variety of material and spiritual factors, including the environment, physical and architectural environment, the social environment and types of activities, the level of culture and history, personal and psychological dimensions (perception, cognition, and feeling). Attention to the identity of places that play an essential role in the socio-humanitarian and urban structure is essential in today's society. Social events in residential districts of cities play a vital role in the vivacity of their inhabitants. The present study explores the attachment to the neighborhood among the inhabitants of the Navvab residential district between Komeyl Street and Mortazavi Street. The present study was a survey method in which data was collected using questionnaires and interviews.  The main questions of the present research are, how is the status of neighborhood attachment among residents in the Navvab district? What is the effect of this phenomenon? How can the attachment in people be enhanced by designing the environment? What are the potential capabilities of the environment, and what is the impact of planning on improving the neighborhood? Findings indicate that the variables of local social ties, access to facilities and educations, the sense of security and social order, age of people have a high impact on the attachment to the residential district. Also, people who are more satisfied with their neighborhood are likely to have more attachment to their neighborhood identity. Indigenous people living in the neighborhood (the effect of the length of stay) have more attachment to their neighborhood than non-indigenous people. The more the security of inhabitant of the neighborhood, the more the attachment of the inhabitants becomes

Additive manufactured high entropy alloys:A review of the microstructure and properties

High entropy alloys (HEAs) are promising multi-component alloys with unique combination of novel microstructures and excellent properties. However, there are still certain limitations in the fabrication of HEAs by conventional methods. Additive manufactured HEAs exhibit optimized microstructures and improved properties, and there is a significantly increasing trend on the application of additive manufacturing (AM) techniques in producing HEAs in recent years. This review summarizes the additive manufactured HEAs in terms of microstructure characteristics, mechanical and some functional properties reported so far, and provides readers with a fundamental understanding of this research field. We first briefly review the application of AM methods and the applied HEAs systems, then the microstructure including the relative density, residual stress, grain structure, texture and dislocation networks, element distribution, precipitations and the influence of post-treatment on the microstructural evolution, next the mechanical properties consisting of hardness, tensile properties, compressive properties, cryogenic and high-temperature properties, fatigue properties, creep behavior, post-treatment effect and the strengthening mechanisms analysis. Thereafter, emerging functional properties of additive manufactured HEAs, namely the corrosion resistance, oxidation behaviors, magnetic properties as well as hydrogen storage properties are discussed, respectively. Finally, the current challenges and future work are proposed based on the current research status of this topic