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1.
Summary The fracture behavior of a functionally graded material (FGM) plate subjected to a thermal shock is studied. A surface crack
is considered. The thermomechanical properties of the FGM plate are assumed to vary along the thickness direction. By using
a perturbation method, the transient temperature field is solved. Then the transient thermal stresses and the corresponding
thermal stress intensity factor (TSIF) are obtained. The transient thermal stresses and TSIF in an FGM ceramic/metal (ZrO2/Ti-6Al-4V) plate are shown in figures.
Dedicated to Professor Franz Ziegler on the occasion of his 70th birthday 相似文献
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3.
The effects of SiC and B4C additives in the MoSi2 matrix on the microstructures and mechanical properties at room temperature were investigated. Their coefficients of thermal expansion (CTE) were also evaluated up to 1200°C by a thermal mechanical analysis (TMA). The experimental results show that the Mo2B5 reinforced phase was formed in situ in the hot-pressed MoSi2/SiC/B4C composites. Both the Mo2B5 phase and the SiC phase significantly improved the mechanical behavior of MoSi2. Besides, the SiC with a high content up to 40 vol% could be added into the MoSi2 composite with the B4C additive. As a result, a dense and homogenous MoSi2/SiC/B4C composite was obtained, which possessed a relatively high bending strength and fracture toughness. Meanwhile, the CTE of the MoSi2/SiC/B4C composites linearly decreased with the increasing SiC content, which dropped to 21% at 1200°C in comparison with the pure MoSi2 when adding 40 vol% SiC. This MoSi2/SiC/B4C composite system is very important for developing new applications at elevated temperature, particularly for high-temperature coating applications. 相似文献
4.
Crack Spacing Effect on the Brittle Fracture Characteristics of Semi-infinite Functionally Graded Materials with Periodic Edge Cracks 总被引:2,自引:0,他引:2
The effect of crack spacing on the brittle fracture characteristics of a semi-infinite functionally graded material (FGM) with periodic edge cracks is discussed. The incompatible eigenstrain induced in the material due to mismatch in the coefficients of thermal expansion is considered in the analysis. The nonhomogeneity of the material is simulated by an equivalent eigenstrain, whereby the problem is reduced to that of a cracked homogeneous material with incompatible and equivalent eigenstrains. A method is then formulated to calculate the stress intensity factor of periodic edge cracks in such a semi-infinite homogeneous medium and applied to calculate apparent fracture toughness of a semi-infinite FGM from its prescribed composition profile. Inverse calculation is also carried out to compute composition profile from prescribed apparent fracture toughness of the semi-infinite FGM. Numerical calculations are carried out for semi-infinite TiC/Al2O3 FGM and the results are shown in the figures. 相似文献
5.
《Materials Science & Technology》2013,29(1):57-67
AbstractIn the present study, three aluminium based functionally gradient materials (FGMs), reinforced with different ceramic particulates (silicon carbide, aluminium oxide, and titanium carbide), were successfully synthesised using the innovative gradient slurry disintegration and deposition (GSDD) technique. The results for Al/SiC and Al/Al2O3 revealed, in common, an increase in the weight percentage of reinforcement along the direction of deposition, to result in an increase in porosity and microhardness. However, for Al/TiC, the reverse trend was observed, with porosity and microhardness decreasing with increasing distance from the base of the ingot. The porosity levels for Al/TiC were also found to be significantly lower than those ofthe other two FGMs. Thermomechanical analysis of the FGMs showed thatthe average coefficient of thermal expansion of the high reinforcement end was reduced, as compared to the high aluminium end. Sliding wear test results also revealed that the high reinforcement end was more wear resistant than the high aluminium end, except for the case of Al/Al2O3. An attempt is made to interrelate the effects of different types of particulates, with microstructural development, microhardness and wear rate results obtained in the present study. 相似文献
6.
A method is developed to evaluate stress intensity factors for two diametrically-opposed edge cracks emanating from the inner surface of a thick-walled functionally graded material (FGM) cylinder. The crack and the cylinder inner surfaces are subjected to an internal pressure. The thermal eigenstrain induced in the cylinder material due to nonuniform coefficient of thermal expansion after cooling from the sintering temperature is taken into account. First, the FGM cylinder is homogenized by simulating its nonhomogeneous material properties by an equivalent eigenstrain, whereby the problem is reduced to the solution of a cracked homogenized cylinder with an induced thermal and an equivalent eigenstrains and under an internal pressure. Then, representing the cracks by a continuous distribution of edge dislocations and using their complex potential functions, generalized formulations are developed to calculate stress intensity factors for the cracks in the homogenized cylinder. The stress intensity factors calculated for the cracks in homogenized cylinder represents the stress intensity factors for the same cracks in the FGM cylinder. The application of the formulations are demonstrated for a thick-walled TiC/Al2O3 FGM cylinder and some numerical results of stress intensity factors are presented for different profiles of material distribution in the FGM cylinder. 相似文献
7.
In the present work, a 2124/15 vol%MoSi2 composite was obtained by powder metallurgy. Its microstructure and mechanical properties were investigated at room and at
high temperature (up to 200°C) in conditions T351, T4 and after heat treatments at 495°C for up to 100 h. Up to 150°C, tensile
properties of 2124/MoSi2 in T351 resulted similar to those of a ceramic reinforced 2124/SiC composite. Yield stress of the 2124/MoSi2 material, after heating at 495°C for up to 100 h, resulted higher than that of the monolith 2124 alloy heated for the same
periods. No diffusion reaction phases were formed surrounding the MoSi2 reinforcing particles during such long exposures to high temperature. Only at 100 h, large plate-like precipitates that contain
Al, Cu, Mg and Si appeared. The high thermal stability of this 2124/MoSi2 composite and its good mechanical properties at room and at elevated temperature makes MoSi2 intermetallic a competitor of ceramic reinforcements. 相似文献
8.
MoSi2-RBSC composite samples were prepared by infiltration of Si-2 at.% Mo melt into a preform of commercial SiC and petroleum
coke powder. The infiltrated sample had a density > 92% of the theoretical density (TD) and microstructurally contained SiC,
MoSi2, residual Si and unreacted C. The material was tested for indentation fracture toughness at room temperature with a Vicker’s
indenter andK
IC was found to be 4.42 MPa√m which is around 39% higher than the conventional RBSC material. Enhancement in indentation fracture
toughness is explained in terms of bowing of propagating cracks through MoSi2/SiC interface which is under high thermal stress arising from the thermal expansion mismatch between MoSi2 and SiC. 相似文献
9.
This study concerns the inverse problem of evaluating the optimum material distribution for desired fracture characteristics in a thick-walled functionally graded material (FGM) cylinder containing two diametrically-opposed edge cracks emanating from the inner surface of the cylinder. The thermal eigenstrain developed in the cylinder material due to nonuniform coefficient of thermal expansion as a result of cooling from sintering temperature is taken into account. Based on a generalized method of evaluating stress intensity factors developed in a previous study, an inverse method is developed to optimize material distribution intending to realize prescribed apparent fracture toughness in the FGM cylinder. To present some numerical results, a TiC/Al2O3 FGM cylinder is considered and the inverse problems are solved to evaluate material distributions for two examples of prescribed apparent fracture toughness. The effect of cylinder wall thickness on the material distribution and comparison of material distributions corresponding to a single and two cracks are also discussed. The numerical results reveal that the apparent fracture toughness of FGM cylinders can be controlled by choosing the material distributions properly. 相似文献
10.
Fracture Mechanics Analysis Model for Functionally Graded Materials with Arbitrarily Distributed Properties 总被引:3,自引:0,他引:3
Functionally Graded Materials (FGMs) have been developed as super-resistant materials for propulsion systems and airframe of space-planes in order to decrease thermal stresses and to increase the effect of protection from heat. It has been experimentally observed that surface cracking in FGMs is the most common failure mode of a metal-ceramic FGM when it is subjected to a thermal shock. Therefore, it is very important to consider the thermally induced fracture behaviors of FGMs. In this paper, a functionally graded material strip containing an embedded or a surface crack perpendicular to its boundaries is considered. The graded region is treated as a large number of single layers, with each layer being homogeneous material. The problem is reduced to an integral equation and is solved numerically. Unlike most of the existing researches, which considered only certain assumed material distributions, the method developed in this paper can be used to investigate functionally graded materials with arbitrarily varied material properties. 相似文献
11.
Tetragonal zirconia polycrystal (TZP)/stainless steel 304 (SUS304)- and ZT [50 vol % monoclinic zirconia polycrystal (MZP) + 50 vol % TZP]/SUS304-functionally gradient material (FGM) were fabricated by pressureless sintering, and the sintering properties and residual stresses of this proposed FGM were compared with directly jointed material. The defects in the sintered specimens, such as warping, frustum formation, delamination, and cracking, which originated from the different shrinkage and sintering behavior of ceramic and metal, could be controlled by the adjustments in terms of the particle size and phase type of zirconia. The residual stresses induced on the ceramic and metal regions of FGM were characterized by the X-ray diffraction method, which were relaxed as the thickness and number of compositional gradient layers were increased. The residual stresses in TZP/SUS304-FGM show irregular patterns resulting from sintering defects and thermal expansion mismatch. In ZT/SUS304-FGM, compressive stress is induced on the ceramic regions by the volume expansion of MZP that resulted from the t m ZrO2 phase transformation on cooling. Also, compressive stress is induced on the metal regions by the constraint of warping and frustum formation that must be created to the metal direction caused by the difference of the coefficient of thermal expansions. As a consequence, it has been verified that the residual stresses generated on FGM are dominantly influenced by the thickness and number of compositional gradient layers, and the sintering defects and residual stresses can be controlled by the decrease of the difference of the shrinkage and sintering behavior of each component. 相似文献
12.
For the first time, ceramic precursors were applied in the powder metallurgy (P/M) preparation of Functionally Graded Materials
(FGM). Two types of FGMs were prepared: Al/SiC for possible aerospace applications and Cu/SiC for dynamic seal applications.
There are two main advantages of using ceramic precursors for P/M preparation of FGMs (1) avoidance of the commercially used
debinding step and (2) shrinkage control of the individual layers of the composite.
This revised version was published online in November 2006 with corrections to the Cover Date. 相似文献
13.
《Composites Part B》2007,38(2):201-215
Nonlinear thermal bending analysis is presented for a simply supported, shear deformable functionally graded plate without or with piezoelectric actuators subjected to the combined action of thermal and electrical loads. Heat conduction and temperature-dependent material properties are both taken into account. The temperature field considered is assumed to be a uniform distribution over the plate surface and varied in the thickness direction and the electric field considered only has non-zero-valued component EZ. The material properties of functionally graded materials (FGMs) are assumed to be graded in the thickness direction according to a simple power law distribution in terms of the volume fractions of the constituents, and the material properties of both FGM and piezoelectric layers are assumed to be temperature-dependent. The governing equations of an FGM plate are based on a higher order shear deformation plate theory that includes thermo-piezoelectric effects. A two step perturbation technique is employed to determine the thermal load–deflection and thermal load–bending moment curves. The numerical illustrations concern nonlinear bending response of FGM plates without or with surface bonded piezoelectric actuators due to heat conduction and under different sets of electric loading conditions. The results reveal that for the case of heat conduction the nonlinear thermal bending responses are quite different to those of FGM plates subjected to transverse mechanical loads, and the temperature-dependency of FGMs could not be neglected in the thermal bending analysis. 相似文献
14.
《Composites Science and Technology》2002,62(7-8):1063-1077
This study is concerned with the inverse problem of calculating material distributions intending to realize prescribed apparent fracture toughness in functionally graded material (FGM) coatings around a circular hole in infinite elastic media. The incompatible eigenstrain induced in the FGM coatings after cooling from the sintering temperature, due to mismatch in the coefficients of thermal expansion, is taken into consideration. An approximation method of determining stress intensity factors is introduced for a crack in the FGM coatings in which the FGM coatings are homogenized simulating the nonhomogeneous material properties by a distribution of equivalent eigenstrain. A radial edge crack emanating from the circular hole in the homogenized coatings is considered for the case of a uniform pressure applied to the surfaces of the hole and the crack. The stress intensity factors determined for the crack in the homogenized coatings represent the approximate values of the stress intensity factors for the same crack in the FGM coatings, and are used in the inverse problem of calculating material distributions in the FGM coatings intending to realize prescribed apparent fracture toughness in the coatings. Numerical results are obtained for a TiC/Al2O3 FGM coating, which reveal that the apparent fracture toughness in FGM coatings around a circular hole in infinite elastic media can be controlled within possible limits by choosing an appropriate material distribution profile in the coatings. 相似文献
15.
A K Kuruvilla V V Bhanuprasad K S Prasad Y R Mahajan 《Bulletin of Materials Science》1989,12(5):495-505
In the development of metal-matrix composites, reinforcements of aluminium and its alloys with ceramic materials has been
pursued with keen interest for quite sometime now. However, a systematic comparison of the effect of different reinforcements
in powder-processed aluminium and its alloys is not freely available in the published literature. This study examines the
influence of SiC, TiC, TiB2 and B4C on the modulus and strength of pure aluminium. B4C appears slightly superior as a reinforcement when comparing the effect of SiC, TiC, B4C and TiB2 on specific modulus and specific strength values of composites. However, TiC appears to be a more effective reinforcement,
yielding the best modulus and strength values among those considered in this study. The differences in thermal expansion characteristics
between aluminium and the reinforcements do not seem to explain this observation. The other advantage of TiC is that it is
economically a more viable candidate as compared to B4C and TiB2 for reinforcing aluminium alloys. It is suggested that the superior effect of TiC as a reinforcement is probably related
to the high integrity of the bond at the Al-TiC interface. 相似文献
16.
17.
Charles E. Anderson Jr. Thilo Behner Dennis L. Orphal Arthur E. Nicholls Douglas W. Templeton 《International Journal of Impact Engineering》2008
We have conducted a series of experiments to examine projectile penetration of cylindrical hot-pressed silicon carbide (SiC) ceramic targets that are pre-damaged to varying degrees under controlled laboratory conditions prior to ballistic testing. SiC was thermally shocked to introduce non-contiguous cracks. Another set of targets was thermally shocked and then additional damage was induced by load–unload cycling in an MTS machine while the ceramic specimen was confined in a 7075-T6 aluminum sleeve. Finally, targets were made by compacting SiC powder into a 7075-T6 aluminum sleeve. For each of these target types, long gold rod penetration was measured as a function of impact velocity vp over the approximate range of 1–3 km/s, with most data between 1.5 and 3 km/s. Penetration as a function of time was measured using multiple independently timed flash X-rays. Results are compared with previous results for non-damaged (intact) SiC targets. Key results from these experiments include the following: (1) penetration is nominally steady state for vp>1.5 km/s; (2) for all target types, the penetration velocity u is a linear function of vp (except for the lowest impact velocities); and (3) it is found that uintact<upre-damaged<uin-situ comminuted<upowder<uhydrodynamic. 相似文献
18.
Microstructure and thermal shock resistance of Al2O3 fiber/ZrO2 and SiC fiber/ZrO2 composites fabricated by hot pressing 总被引:1,自引:0,他引:1
Al2O3 chopped fiber/ZrO2 and SiC continuous fiber/ZrO2 composites were fabricated by hot pressing at 1550°C and 15 MPa in vacuum. The mechanical properties of thermally shocked composites were measured at room temperature by four-point bending. The addition of Al2O3 fibers into ZrO2 matrix degraded the fracture strength, but improved significantly the thermal shock resistance. In addition, the mechanical properties of SiC fiber/ZrO2 composites were much lower than those of monolithic ZrO2 because of the presence of microcracks on the surface. The SiC fiber/ZrO2 composites showed an excellent thermal shock resistance. 相似文献
19.
A.M. Afsar 《Engineering Fracture Mechanics》2010,77(14):2919-2926
This study describes the effect of FGM coating thickness on apparent fracture toughness (AFT) of a thick-walled cylinder containing two diametrically-opposed edge cracks emanating from the inner surface of the cylinder. The incompatible eigenstrain developed in the cylinder due to nonuniform coefficient of thermal expansion because of cooling from sintering temperature is taken into account. Based on a generalized method of evaluating stress intensity factor (SIF) addressed in a previous study, an approach is developed to calculate AFT. Some numerical results of AFT are presented for a TiC/Al2O3 FGM coating at the inner surface of an Al2O3 thick-walled cylinder. 相似文献
20.
《Materials Science and Engineering: A》2007,443(1-2):60-65
A technique used to improve the life cycle and/or the working temperature of the turbine blades uses ceramic coatings over metallic material applied by electron beam-physical vapor deposition (EB-PVD). The most usual material for this application is yttria doped zirconia. Addition of niobia, as a co-dopant in the Y2O3–ZrO2 system, can reduce thermal conductivity. The purpose of this work is to evaluate the influence of the addition of niobia on the microstructure and thermal properties of the ceramic coatings. This new formulation will, in the future, be able to become an alternative to the composition currently used by the aerospace field in EB-PVD thermal barrier coatings (TBC). A significant reduction of the thermal conductivity, measured by laser flash technique, in the zirconia ceramic coatings co-doped with yttria and niobia when compared with zirconia–yttria coatings was observed. 相似文献