Metal Matrix Composites as Potential Armour Materials

To defeat a kinetic energy projectile the armour needs to be extremely hard on the surface, so as to blunt the projectile on initial impact. A ceramic material may be an ideal choice. However, to absorb and dissipate the complete kinetic energy of the projectile, the subsequent material has to be extremely tough with a very high work of fracture. It also needs to be a light weight material to keep the overall weight to a minimum possible value. A fibre reinforced polymer matrix composite can meet the requirement. The innermost laver needs to have a very high ductility so as to avoid any fracture and fragment formation which could be lethal. So it has to be a metallic material. Thus, the application requires a range of properties starting from that of a ceramic and ending with that of a metal. Metal matrix composites (MMCs) are essentially metals reinforced with ceramic reinforcements, which exhibit a combination of properties of both the constituents and could be tailored to suit the requirements. Discontinuously reinforced MMCs also have the added advantage of being amenable to conventional metal forming operations, which makes it easier to produce them in the required shapes. This paper would provide an introduction to MMCs and review the available literature on their evaluation for possible applications as armour materials.It would also present the results of the preliminary studies on the dynamic hardness measurements of discontinuously reinforced aluminium alloy composites which gives a good indication of their potential use as armour materials

Association of Accelerometry-Measured Physical Activity and Cardiovascular Events in Mobility-Limited Older Adults: The LIFE (Lifestyle Interventions and Independence for Elders) Study.

BACKGROUND:Data are sparse regarding the value of physical activity (PA) surveillance among older adults-particularly among those with mobility limitations. The objective of this study was to examine longitudinal associations between objectively measured daily PA and the incidence of cardiovascular events among older adults in the LIFE (Lifestyle Interventions and Independence for Elders) study. METHODS AND RESULTS:Cardiovascular events were adjudicated based on medical records review, and cardiovascular risk factors were controlled for in the analysis. Home-based activity data were collected by hip-worn accelerometers at baseline and at 6, 12, and 24 months postrandomization to either a physical activity or health education intervention. LIFE study participants (n=1590; age 78.9±5.2 [SD] years; 67.2% women) at baseline had an 11% lower incidence of experiencing a subsequent cardiovascular event per 500 steps taken per day based on activity data (hazard ratio, 0.89; 95% confidence interval, 0.84-0.96; P=0.001). At baseline, every 30 minutes spent performing activities ≥500 counts per minute (hazard ratio, 0.75; confidence interval, 0.65-0.89 [P=0.001]) were also associated with a lower incidence of cardiovascular events. Throughout follow-up (6, 12, and 24 months), both the number of steps per day (per 500 steps; hazard ratio, 0.90, confidence interval, 0.85-0.96 [P=0.001]) and duration of activity ≥500 counts per minute (per 30 minutes; hazard ratio, 0.76; confidence interval, 0.63-0.90 [P=0.002]) were significantly associated with lower cardiovascular event rates. CONCLUSIONS:Objective measurements of physical activity via accelerometry were associated with cardiovascular events among older adults with limited mobility (summary score >10 on the Short Physical Performance Battery) both using baseline and longitudinal data. CLINICAL TRIAL REGISTRATION:URL: http://www.clinicaltrials.gov. Unique identifier: NCT01072500

ZrB2–SiC based composites for thermal protection by reaction sintering of ZrO2+B4C+Si

Abstract Synthesis and sintering of ZrB2–SiC based composites have been carried out in a single-step pressureless reaction sintering (PLRS) of ZrO2, B4C, and Si. Y2O3 and Al2O3 were used as sintering additives. The effect of ratios of ZrO2/B4C, ZrO2/Si, and sintering additives (Y2O3 and Al2O3), was studied by sintering at different temperatures between 1500 and 1680 °C in argon atmosphere. ZrB2, SiC, and YAG phases were identified in the sintered compacts. Density as high as 4.2 g/cm3, micro hardness of 12.7 GPa, and flexural strength of 117.6 MPa were obtained for PLRS composites. Filler material was also prepared by PLRS for tungsten inert gas (TIG) welding of the ZrB2–SiC based composites. The shear strength of the weld was 63.5 MPa. The PLRS ZrB2–SiC composites exhibited: (i) resistance to oxidation and thermal shock upon exposure to plasma flame at 2700 °C for 600 s, (ii) thermal protection for Cf–SiC composites upon exposure to oxy-propane flame at 2300 °C for 600 s

The effect of participate reinforcement on the sliding wear behavior of aluminum matrix composites

The aim of the present investigation is to characterize the friction and wear behavior of aluminum matrix composites reinforced with particulates of SiC, TiC, TiB2, and B4C. Sliding wear tests were conducted at two loads (80 and 160 N) using a pin-on-disc apparatus and under dry conditions. The results of the investigation indicate that the coefficient of friction of the composites is about 30 pct lower than that of pure aluminum, while the wear rates of the com- posites are lower by a factor of about 3 and 100 at loads of 80 and 160 N, respectively. The type and size of the reinforcement have a negligible influence on the wear rate and the coefficient of friction of the composites. However, the volume fraction of the reinforcement has a marginal influence on the wear rate. Though the coefficients of friction and the wear rates of the composites were broadly similar, the Al-TiC composite alone exhibits a somewhat higher wear rate. The above results of the present investigation have been rationalized on the basis of the inverse rule of mixtures and the existing models for friction and wear

Recent development in the fabrication of metal matrix-particulate composites using powder metallurgy techniques

10.1007/BF01154673Journal of Materials Science2981999-2007JMTS