Abstract: The vibration band gaps of one dimensional phononic crystal of rod structure consisted of Ti and Rubber were studied using the lumped-mass method and finite element simulation, the influences of vibration band gap by the periodicity and volume fraction were discussed. The results show that the initial frequency and cutoff frequency have little influence by the periodicity, but the anti-vibration effect is more effective as the periodicity increases; the cutoff frequency gradually decreases, the initial frequency decreases first and then increases as the volume fraction increases.
Abstract: Measurement of wheel/rail contact forces is of importance. Traditional methods for wheel/rail interaction force measurement all need strain gauges on wheel sets and/or rails. Because strain gauges have the performances of zero-drift, poor anti-interference property and instability of test system, they can’t meet wheel/rail force test requirements in high-speed and heavy haul railways. A new method based on PVDF piezoelectric sensing technology is presented for the test of vertical and horizontal wheel/rail force in this paper. Firstly, based on the wheel/rail interaction characteristics, the restriction condition of track and strain sensing principle of PVDF films, principle for measuring vertical and lateral wheel/rail interaction forces is proposed. Then a series of tests were carried out to compare the performance of PVDF strain sensors with the one of strain gauges. The results show that the PVDF strain sensor has better reliability in wheel/rail force monitoring. Finally numerical analysis by Finite Element Method has been carried out to verify the feasibility of the method presented in this paper.
Abstract: A new procedure, thixo-die-forging of ceramics/metal composite in the pseudo-semi-solid state, has been proposed based on powder metallurgy combining with the semi-solid processing of metal. The cup-shaped parts of Al/Al2O3 composite are processed with thixo-die-forging. By metallographic analysis and performance tests, the results show that microstructures are compact, grains are fine and mechanical properties are excellent. The bend strength and fracture toughness of 37vol.%Al/Al2O3 are about 430-690MPa and 8.5-16.8 MPa•m1/2 respectively. Comparing with those of the reaction in situ and high temperature oxidation procedures, the bend strength increases by 50% and 80%, and fracture toughness increases by 29% and 55%, respectively. The results also show that the processing parameters, such as temperature and pressure have great influences on the properties. Thixo-die-forging in the pseudo-semi-solid state can prepare Al/Al2O3 composite with high performance.
Abstract: The 80Ni20Cr coatings on cotton fabric substrates using the electron beam evaporated deposition are reported to improve the electrical conductivity of fabric substrates. The cotton fabrics are coated twice for single-faced NiCr film and one time per face for double-faced NiCr film, respectively. The morphology of coatings is characterized by an optical microscopy. The effect of sample length and test orientation of warp-wise and weft-wise on electrical conductivity is measured. It is found that the NiCr coatings dramatically increase the electrical conductivity of cotton fabrics. For warp-wise orientation with lengthwidth (4 cm1 cm) of test sample, the surface resistance is about 0.7 MΩ for single-faced coating and 0.89 MΩ for double-faced coating, while the surface resistance of raw cotton fabric is above 104 MΩ. The results tested from warp-wise and weft-wise are uniform, which is mainly because of the structure balance of the plain fabrics. The microstructure observation indicates that the single-faced coatings are uniform and dense, and the present double-faced coating processes are not enough to completely cover the fabric substrates. The uniform and dense coatings of single-faced NiCr coatings could be the reason that the electrical conductivity is better than that of the present double-faced NiCr coating.
Abstract: Calcium phosphate cement (CPC) sets in situ to form solid hydroxyapatite, can conform to complex cavity shapes without machining, has excellent osteoinductivity, and is able to be resorbed and replaced by new bone. Therefore, CPC is promising for craniofacial and orthopaedic repairs. However, its low strength and lack of macroporosity limit its use. This study investigated CPC reinforcement with absorbable fibers, the effects of fiber volume fraction on mechanical properties and macroporosity, and the biocompatibility of CPC-fiber composite. The liquid phase of CPC in this study was the weak acidic solution of chitosan. Chitosan has favourable biocompatibility, which has high viscosity in solution. The incorporation of chitosan could improve the handling properties of CPC. The liquid phase contained citric acid could strongly improve the hydration rate of CPC, which shortened the setting time and increased the compressive strength of CPC. In addition, the weak acidic environment around the biomaterials could accelerate the degradation of CPC, which was important to bone tissue engineering. The rationale was that large-diameter absorbable fibers would initially strengthen the CPC graft, then dissolve to form long cylindrical macropores for colonization by osteoblasts. Compressive strength was measured vs. fiber volume fraction from 0% (CPC Control without fibers) to 70%. Animal experiment showed that the material had osteoinductivity and biodegradability when the material was implanted into the muscle pouches in the thigh of rabbits. Compressive strength (mean ± SD; n=3) of CPC with 70% fibers was 0.8± 0.1 MPa. Long cylindrical macropores 100~300 μm in diameter were created in CPC after fiber dissolution, and the CPC-fiber scaffold reached a total porosity of 75.1±1.2% with 70% fibers. The new CPC-fiber formulation had good potentiality of ectopic bone induction. The method of using large-diameter absorbable fibers in bone graft for mechanical properties and formation of long cylindrical macropores for bone ingrowth may be applicable to other tissue engineering materials.
Abstract: Three fillers i.e. micro glass bead, nano-montmorillonite and graphite at 8wt% were respectively filled into ultrahigh molecular weight polyethylene (UHMWPE). The microstructure, mechanical properties were investigated. The results indicated that: The performances of three kinds of composites, such as morphology, tensile strength, impact strength, elongation at break and fraction wear, were in great difference. The bonding of interface between glass bead and UHMWPE was not firm, but nano-montmorillonite and graphite as filler dispersed in matrix evenly and coupling tight. Due to filling the filler, the tensile strength, impact strength and elongation at break decreased in varying degree compared with that of simple UHMWPE, but impact strengths reduced only a few; however the wear resistance of composite filled by graphite was improved obviously.
Abstract: Metal rubber material is a new type of elastic and porous material which develops from metal materials. The macro-structure of metal rubber is reticular just as high polymer, made up of fine metal wires. In this paper, the testing equipment which can test micro-motion of metal rubber is designed and the compressive force-displacement curve along molding of metal rubber has gain. The cure along molding of metal rubber has three different characteristic stages. In different characteristic stages, the deformation of metal rubber material has different micro physical mechanism. The micro physical mechanism of different deformation periods is summarized by the micro analyses of three different characteristic curve stages and the study of metal rubber molding technology. Based on the manufacture technology and molding process, the spring wires in metal rubber material have contacted adequately after molding. The micro physical mechanism of metal rubber material in this stage is produced by blank tear combination deformation in linear elastic of spring wires. Because of the deformation stage is very little; the stiffness of metal rubber material is represented linear characteristic in this stage. The contacted points of spring wires are slide along with deformation increasing. The stiffness of metal rubber material is reduced after early linear deformation stage. The compressive force-displacement curve represents soft characteristic stage in macro- expression. When the most contacted points of spring wires are slide along with deformation increasing, the stiffness of metal rubber material is rapid rise. The exponential reinforcement stage is caused by the strongly constraints among spring wires. The micro physical mechanism can explain the different characteristic stages of metal rubber material on compressive performance.
Abstract: 2-2 cement based piezoelectric composite was fabricated using sulphoaluminate cement and lead magnesium niobate-lead zirconate-lead titanate ceramic (P(MN)ZT) by dice-and-fill technique. The effects of composite thickness on dielectric, piezoelectric and electromechanical properties of the composite were analyzed, respectively. The results show that the increase of composite thickness will improve the piezoelectric strain factor d33 of the composite, while decreases the piezoelectric voltage factor g33 of the composite. The relative dielectric factor εr as well as the dielectric loss tan δ of the composite also increases with increasing the thickness. The electromechanical analysis results show that the thickness electromechanical coupling coefficient Kt of the composite increases obviously with decreasing the thickness, meanwhile the mechanical quality factor Qm of the composite shows the increasing trend, thus, the receiving piezoelectric transducers can be fabricated by decreasing the thickness.