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This paper focuses on helmet design for head protection under blast threats. It is presented a numerical investigation of the head response accruing to blast loads on helmet protective systems. Various combinations of the helmet, visor and mandible guard were numerically analyzed for a given mass of TNT at a distance to the target representing an anti-vehicle buried mine threat. Limited published articles on the subject are available in the scientific literature. In this paper, a 3D head–helmet numerical model for blast analyses is developed in the finite element code ABAQUS/Explicit. The results showed that individual protective systems are not effective enough to mitigate the damage caused by blast loading. The complete protective equipment reduces the pressures on the brain by up to 5 times and ensures that no fracture in the skull appears. This numerical study aims to provide helmet manufacturers and users with some insight in what possible brain injuries are to be expected in various blast scenarios so as to help in better diagnosis of unsuspected brain injury. [ABSTRACT FROM AUTHOR]

Abstract: The increasing demand for portable electronics has led to the shrinking in size of electronic components and solder joint dimensions. The industry also made a transition towards the adoption of lead-free solder alloys, commonly based around the Sn–Ag–Cu alloys. As knowledge of the processes and operational reliability of these lead-free solder joints (used especially in advanced packages) is limited, it has become a major concern to characterise the mechanical performance of these interconnects amid the greater push for greener electronics by the European Union. In this study, bulk solder tensile tests were performed to characterise the mechanical properties of SAC 105 (Sn–1%wt Ag–0.5%wt Cu) and SAC 405 (Sn–4%wt Ag–0.5%wt Cu) at strain rates ranging from 0.0088s−1 to 57.0s−1. Solder joint array shear and tensile tests were also conducted on wafer-level chip scale package (WLCSP) specimens of different solder alloy materials under two test rates of 0.5mm/s (2.27 s−1) and 5mm/s (22.73 s−1). These WLCSP packages have an array of 12×12 solder bumps (300μm in diameter); and double redistribution layers with a Ti/Cu/Ni/Au under-bump metallurgy (UBM) as their silicon-based interface structure. The bulk solder tensile tests show that Sn–Ag–Cu alloys exhibit higher mechanical strength (yield stress and ultimate tensile strength) with increasing strain rate. A rate-dependent model of yield stress and ultimate tensile strength (UTS) was developed based on the test results. Good mechanical performance of package pull-tests at high strain rates is often correlated to a higher percentage of bulk solder failures than interface failures in solder joints. The solder joint array tests show that for higher test rates and Ag content, there are less bulk solder failures and more interface failures. Correspondingly, the average solder joint strength, peak load and ductility also decrease under higher test rate and Ag content. The solder joint results relate closely to the higher rate sensitivity of SAC 405 in gaining material strength which might prove detrimental to solder joint interfaces that are less rate sensitive. In addition, specimens under shear yielded more bulk solder failures, higher average solder joint strength and ductility than specimens under tension. [Copyright &y& Elsevier]

Abstract: Single solder interconnects were subjected to a series of combined tension–shear and compression–shear tests to determine their failure load. The failure envelope of these interconnects was obtained by plotting the normal component against the shear component of the failure load. The interconnect failure force map was found to be elliptical like the failure envelopes of many materials. The failure map can be described by a simple mathematical expression to give a simple force-based criterion for combine loading of solder joints. Post mortem analyses were conducted on the solder joint specimens to identify the failure mechanisms associated with various segments of the failure map. Computational simulations of actual board tests show that the failure map obtained for joint tests provides good predictions of board-level interconnect failures and hence suggest that such failure maps are useful in the design and analysis of board assemblies subjected to mechanical loads. The industry could adopt the methodology to obtain failure envelopes for solder joints of different alloys, bump size and reflow profiles which they could later use to aid in board-level and system-level designs of their products for mechanical reliability. [Copyright &y& Elsevier]

Discusses how the way survival data is analysed statistically and presented can affect clinicians' perception of drug efficacy. Flaws in the presentation of the benefits of drugs by stating the relative risk reduction achieved by the investigational drug, illustrated by Kaplan-Meier survival curves; Example; Need to include presentation of data in terms of extension of lives, not just the saving of lives.

Investigates the beneficial effects of exercise rehabilitation following coronary bypass surgery in Great Britain. Rate of ventilation and oxygen uptake; Increase in peak cardiac output; Increase in functional capacity.