Optimal solutions to the redundancy allocation problem are determined for systems designed with multiple k-out-of-n subsystems in series. The objective is to select the components and redundancy levels to maximize system reliability given system-level constraints. The individual subsystems may use either active or cold-standby redundancy, or they may require no redundancy. Previously, optimization methods for this problem either pertained to k-out-of-n systems consisting of a single subsystem or to series-parallel systems (k = 1). Additionally, it had generally been assumed that only active redundancy was to be used. In practice design problems can vary appreciably from these restrictions and the design process may consider more complex system configurations. Unfortunately, available optimization algorithms are inadequate for many of these design problems. The methodology presented here is specifically developed to accommodate the case with k-out-of-n subsystems. Optimal solutions to the problem are found by an equivalent problem formulation and integer programming. The methodology is demonstrated on a well-known test problem with interesting results. The availability of this tool fills a void and should result in more reliable and cost-effective engineering designs.
In order to improve the mechanical properties of hollow glass microspheres (HGMs) reinforced epoxy resin composite, diluent was added in the system of epoxy resin. The results revealed that more HGMs can be filled in the epoxy resin when appropriate amount diluent was added in the system, thus composite with relative low bulk density 0.70g/cm3 and high compressive strength 71.85MPa was obtained. It was due to that the diluent reduce the viscosity of the epoxy resin, which ensures uniform wetting of the fillers and enables more HGMs to be filled in resin. Besides, addition of diluent improved the adhesive strength between the epoxy resin and HGMs, making the composite having a relative high specific strength and can be used in weight sensitive filed.
A heat-resistant phosphate adhesive was developed for joining and repairing of C/C composites. The high-temperature bonding effect for both cured adhesive and 1300°C-calcined adhesive had been evaluated through testing high-temperature shear strength of corresponding joints. The results showed that the bonding strength of cured adhesive decreased from 7.9 MPa at RT to 0.9 MPa at 1300°C, while that of 1300°C-calcined adhesive could maintain about 4 MPa at temperature range from RT to 700°C and then decreased to 1.7 MPa at 1300°C. Besides, with the increasing thermal cycling times at 1300°C, the high-temperature bonding strength at this temperature could maintain at about 2.3 MPa.
Effects of Al in different added condition on pores shape and mullite configuration were investigated. Three sorts of hole were got by using Al as foaming agent in mullite composites. It was concluded that isolated holes could be formed by Al changing to Al2Ol3 with acidity condition in green state, open holes could be formed by Al changing to Al2O3 directly in sintering process, and mixed hole of isolated and open ones could be formed by Al changing to Al(OH)3 with alkalescence condition in green state followed changing to Al2O3 in sintering process. These holes could supply a position for growth of mullite as well.
A light weight and heat-resistant composite material was successfully fabricated by impregnation-filtration process in which Al2O3-SiO2 fiber mat was used as the skeleton and silica was applied as reinforcing filler. The effects of both concentration of silica sol and sintering temperature on SiO2/Al2O3-SiO2 fiber composites were studied. The results indicated that the density of composites increased with the concentration of silica sol increasing. The heat-treatment temperature had little effect on the density of composites. As heat-treatment temperature increased, the compressive strength increased firstly and then decreased.
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