In the present work, mechanisms are proposed for solidification crack initiation and growth in aluminum alloy 6060 arc welds. Calculations for an interdendritic liquid pressure drop, made using the Rappaz-Drezet-Gremaud (RDG) model, demonstrate that cavitation as a liquid fracture mechanism is not likely to occur except at elevated levels of hydrogen content. Instead, a porosity-based crack initiation model has been developed based upon pore stability criteria, assuming that gas pores expand from pre-existing nuclei. Crack initiation is taken to occur when stable pores form within the coherent dendrite region, depending upon hydrogen content. Following initiation, crack growth is modeled using a mass balance approach, controlled by local strain rate conditions. The critical grain boundary liquid deformation rate needed for solidification crack growth has been determined for a weld made with a 16 pct 4043 filler addition, based upon the local strain rate measurement and a simplified strain rate partitioning model. Combined models show that hydrogen and strain rate control crack initiation and growth, respectively. A hypothetical hydrogen strain rate map is presented, defining conceptually the combined conditions needed for cracking and porosity.

Objectives Given the growing support for establishing a just patient safety culture in healthcare settings, a valid tool is needed to assess and improve just patient safety culture. The purpose of this study was to develop a measure of individual perceptions of just culture for a hospital setting. Methods The 27 item survey was administered to 998 members of a healthcare staff in a pediatric research hospital as part of the hospital's ongoing patient safety culture assessment process. Subscales included balancing a blame-free approach with accountability, feedback and communication, openness of communication, quality of the event reporting process, continuous improvement, and trust. The final sample of 404 participants (40% response rate) included nurses, physicians, pharmacists and other hospital staff members involved in patient care. Confirmatory factor analysis was used to test the internal structure of the measure and reliability analyses were conducted on the subscales. Results Moderate support for the factor structure was established with confirmatory factor analysis. After modifications were made to improve statistical fit, the final version of the measure included six subscales loading onto one higher-order dimension. Additionally, Cronbach's alpha reliability scores for the subscales were positive, with each dimension being above 0.7 with the exception of one. Conclusions The instrument designed and tested in this study demonstrated adequate structure and reliability. Given the uniqueness of the current sample, further verification of the JCAT is needed from hospitals that serve broader populations. A validated tool could also be used to evaluate the relation between just culture and patient safety outcomes.

Solidification cracking is a weld defect common to certain susceptible alloys rendering many of them unweldable. It forms and grows continuously behind a moving weld pool within the two phase mushy zone and involves a complex interaction between thermal, metallurgical and mechanical factors. Despite decades long efforts to investigate weld solidification cracking, there remains a significant lack of understanding regarding its underlying mechanisms. Criteria developed to evaluate alloy weldability will be examined in terms of proposed solidification cracking models. Crack initiation is discussed in terms of different criteria: critical stress to fracture the interdendritic liquid, critical strain to exceed the mushy zone ductility and critical hydrogen content to nucleate and grow a pore. Crack growth has been characterised in terms of a critical stress to fracture the liquid film surrounding a grain and critical strain rate interdependent with liquid feeding of the mushy zone opening. Experimental data to form a weld solidification crack are compiled, revealing the considerable amount of information available in the literature on this topic.

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The effect of scandium and titanium–boron (Tibor) additions on the solidification behaviour of castings and welds of aluminium alloy 7108 has been investigated. A circular patch test was adopted to evaluate the effects of these elements on the hot cracking suscepti bility of welds made on cast coupons treated with different grain refiner additions. It was observed that grain size, as well as cracking susceptibility, decreased with increasing amounts of scandium and that hot cracking was completely eliminated at scandium additions above 0·25 wt-%. A more pronounced grain refining effect in welds was observed with Tibor and, in addition, no hot cracking was observed with Tibor additions as low as 0·02 wt-%Ti (0·004 wt-%B). Castings, however, were more effectively grain refined with scandium, achieving a finer grain size than with Tibor.