Experimental observations of tensile fracture in unidirectional boron filament reinforced aluminum sheet

Results are presented from an experimental study of the tensile fracture process in unidirectional boron filament reinforced aluminum sheet. The tensile strength of the material was apparently limited by a noncumulative fracture mechanism which involved the initiation and sustenance of a chain reaction of filament fractures at a relatively low stress level. Matrix fracture followed in a completely ductile manner. The minimum filament stress for initiation of the fracture mechanism was shown to be approximately 170 ksi for well bonded composite having a pure aluminum matrix. This value appeared to be independent of filament diameter, number of filament layers, and filament volume fraction within the range investigated (0.2 to 0.5). Several commonly observed features of tensile fracture surfaces were explained in terms of the observed noncumulative fracture mechanism.     

The transverse tensile properties of boron fiber reinforced aluminum matrix composites

The transverse tensile properties of boron fiber reinforced aluminum have been determined as a function of fabrication parameters, matrix alloy and fiber types, fiber content, specimen geometry, and thermal environment. Matrix alloys investigated include 2024, 6061, 5052, 5056, 2219, 1100, and Al-7 pct Si. The fibers investigated include 4.0 mil boron, 4.2 mil BORSIC, R.F. boron, 5.6 mil boron, 5.7 mil BORSIC, and 4.0 mil silicon carbide. It was shown that the composite transverse tensile performance is a function of all of these variables and that transverse strengths of up to 45,000 psi can be achieved by the choice of the proper combination of matrix, fiber type and fabrication procedures.     

Thermal expansion of boron fiber-aluminum composites

The linear thermal expansion of silicon carbide coated boron (BORSIC^®) aluminum composites was measured as a function of volume fraction fiber and angle with respect to the fiber axis. The measurements were made with a standard quartz tube-type dilatometer at a heating rate of 150°C per hr. Measurements were made between 25° and 300°C on 2024 aluminum alloy-BORSIC and 1100 aluminum alloy-BORSIC composites in the 0 and 90 deg fiber orientation as a function of volume fraction fiber. The axial test results are compared with several models found in the literature which predict composite thermal expansion. These predictions yield values which are higher than the measured expansion coefficients of the 0 deg composites. The discrepancy is assumed to be related to yielding in the matrix. The 90 deg composites are found to agree with the transverse thermal expansion coefficient relationship of Schapery (also Levin) which employs the Poisson ratio for each phase and the composite. The expansion coefficients of 2024 aluminum alloy-BORSIC composites containing 54 pct by volume fiber are given for fiber orientations of 0, 15, 30, 45, 60, 75, and 90 deg.     

Enhanced tensile strength for electrodeposited nickel-copper multilayer composites

The tensile strength of electrodeposited layered composites of the nominal overall composition 90 pct Ni-10 pct Cu is shown to increase sharply to the 1300 MPa range as the thickness of the Cu layers is decreased below ~0.4 ώm. This tensile strength value is almost a factor of three greater than that measured for Ni itself, and more than a factor of two greater than the handbook value for Monel 400.     

The mode I fracture resistance of unidirectional fiber-reinforced aluminum matrix composites

The mode I fracture resistance has been measured for Al and Al/4 Mg matrix composites, unidirectionally reinforced with ceramic fibers, prepared using a squeeze casting technique. Effects of SiC particle additions have also been investigated. The Al/4 Mg system had a high toughness, whereas the Al matrix system had a relatively low fracture resistance. In all cases, the addition of particulates slightly decreased the resistance to crack growth. The fracture resistance was simulated by a ductile bridging model with plastic dissipation occurring within a zone governed by the fiber spacing. The tensile strength of these composites has been estimated, based on the resistance behavior and microstructure.     

The effects of hot pressing parameters on the strength of aluminum/stainless steel composites

Stainless steel fiber reinforced aluminum matrix composites have been fabricated by hot pressing under different conditions of temperature, pressure, and time. The variation in tensile strength of these composites has been studied in detail, and the hot pressing parameters have been optimized in order to fabricate composites having maximum strength at any fiber volume fraction. Microprobe analysis and Scanning Electron Microscopy of these composites have revealed interesting features of fiber/ matrix interface. These features have been found helpful in explaining the dependence of strength of the composites on hot pressing parameters.     

Temperature-dependence mechanism of tensile strength of Si-Ti-C-0 Fiber-Aluminum matrix composites

The mechanism for the temperature dependence of the tensile strength of unidirectional hybrid type Si-Ti-C-O (Tyranno) fiber-reinforced aluminum matrix composite, in which SiC-particles are dispersed in the matrix, is discussed, focusing on the temperature dependencies of the stress concentration arising from broken fibers and critical length and their influences on the composite strength, by means of a shear-lag analysis and a Monte Carlo simulation. The main results are summarized as follows. The softening of the matrix at high temperatures raises the composite strength from the point of decrease in stress concentration, but on the other hand, it also reduces strength from the point of increase in critical length, which reduces the stress-carrying capacity of broken fibers over a long distance. The reason why the measured strength of composite decreased with increasing temperature could be attributed to the predominacy of the latter effect over the former one. The results of the simulation indicated that the hybridization of the composites improved room-temperature and high-temperature strengths through the strengthening of the matrix.     

The effect of thermal cycling on the mechanical properties of various aluminum alloys reinforced with unidirectional boron fibers

The mechanical properties of boron reinforced 6061, 1100, or 2024 aluminum alloys were measured at room temperature in the as-received condition and after thermal cycling. It was observed that cycling these materials through temperatures that varied between room temperature and either 588 K, 638 K, or 698 K could seriously degrade the properties. Observations of the surfaces of some specimens indicated that small perturbations appeared after very few cycles. These widened and deepened as the test proceeded until they developed into macroscopically visible surface cracks. The appearance of these cracks coincided with the maximum degradation of the mechanical properties. The extent of the observed effects depended on alloy type and the maximum cyclic temperature used. Increasing the maximum temperature produced an increase in the damage. The properties of the reinforced 2024 material were the most affected. A smaller degradation was produced in the properties of the 6061 material; however, some of the properties of the reinforced 1100 material were improved slightly.     

粉末冶金法制备铝基碳化硼复合材料的研究进展

本文归纳了粉末冶金法制备铝基碳化硼复合材料的制备工艺, 主要包含混料、压制、烧结、变形等工艺环节; 对铝基碳化硼复合材料主要性能及影响因素做了阐述, 重点整理了材料均匀性、相对密度、力学性能的研究情况; 总结了工程用铝基碳化硼材料的生产及使用情况, 分析几种常见铝基碳化硼产品的特点; 提出采用粉末冶金法生产大尺寸、高品质、低成本的铝基碳化硼材料是未来研究方向之一的观点, 并阐述了工艺优化方案。在核电等相关产业的带动下, 中国有望成为全球铝基碳化硼复合材料生产和研究中心。     

Correlation of tensile strength with fracture modes of KAOWOOL- and SAFFIL-reinforced 339 aluminum

The tensile strengths of composites of 339 aluminum reinforced with either SAFFIL or KAOWOOL fibers are compared over the temperature range of 20 °C to 300 °C. For this type of composite, in which the discontinuous fibers are randomly oriented, the fibers perpendicular to the applied stress play a critical role, which in turn creates a dependence upon the interfacial bond strength. The KAOWOOL fibers form a strong interfacial bond so that tensile failure occurs either in the matrix at 300 °C or by fiber cleavage at 20 °C. In the T5 condition, the SAFFIL interface is weaker than the matrix alloy so that failure occurs by delamination of the transverse fibers. Thus, although the SAFFIL fibers are 40 pct stronger than the KAOWOOL fibers, the T5 composites have the same ultimate tensile strengths. A T6 heat treatment promotes an interfacial reaction with magnesium. This strengthens the SAFFIL interface so that failure occurs primarily in the matrix, producing higher composite strengths. The reaction with the KAOWOOL fibers is so extensive that the matrix, and therefore the composite strength, is drastically decreased. When account is taken of the different fracture modes, together with the matrix strengths as determined by nanoindentation, the calculated values of composite strength are in good agreement with experiment.     

Correlation of tensile strength with fracture modes of KAOWOOL- and SAFFIL-reinforced 339 aluminum

The tensile strengths of composites of 339 aluminum reinforced with either SAFFIL or KAOWOOL fibers are compared over the temperature range of 20°C to 300°C. For this type of composite, in which the discontinuous fibers are randomly oriented, the fibers perpendicular to the applied stress play a critical role, which in turn creates a dependence upon the interfacial bond strength. The KAOWOOL fibers form a strong interfacial bond so that tensile failure occurs either in the matrix at 300 °C or by fiber cleavage at 20°C. In the T5 condition, the SAFFIL interface is weaker than the matrix alloy so that failure occurs by delamination of the transverse fibers. Thus, although the SAFFIL fibers are 40 pct stronger than the KAOWOOL fibers, the T5 composites have the same ultimate tensile strengths. A T6 heat treatment promotes an interfacial reaction with magnesium. This strengthens the SAFFIL interface so that failure occurs primarily in the matrix, producing higher composite strengths. The reaction with the KAOWOOL fibers is so extensive that the matrix, and therefore the composite strength, is drastically decreased. When account is taken of the different fracture modes, together with the matrix strengths as determined by nanoindentation, the calculated values of composite strength are in good agreement with experiment.     

Influences of matrix ductility,interfacial bonding strength,and fiber volume fraction on tensile strength of unidirectional metal matrix composite

A trial to predict the influences of ductility of matrix, interfacial bonding strength, and volume fraction of fiber on the tensile strength of unidirectional metal matrix composites was attempted by means of a Monte Carlo computer simulation method. The main results are summarized as follows. (1) The strength of strongly bonded composites increased with increasing ductility of matrix and then remained nearly constant. (2) When the matrix was ductile, the strength of composite increased with increasing interfacial bonding strength and then remained nearly constant. When the matrix was not ductile, the strength increased but then decreased with interfacial bonding strength. In this case, there was an optimum bonding strength, for which the strength of composite was highest. (3) Concerning the strength of composite as a function of volume fraction of fiber, there arose the case where it is approximately described by the rule of mixtures and also the case where it is not described by this rule, depending on the ductility of matrix, interfacial bonding strength, and scatter of strength of fiber.     

An ultimate tensile strength dependence on processing for consolidated metal matrix composites

The ultimate tensile strength (UTS) of metal and intermetallic matrix unidirectional composites can be significantly lower than expected from the rule of mixtures prediction. One possible explanation is that the fibers in the as-processed state are in a residual state of stress and in some cases are broken because of the inhomogeneous nature of the densification during manufacture. Three main results emerge from the effort to include the effect of this processing damage on the composite UTS. First is the development of a simple but accurate analytical version of Curtin's model for predicting the stress-strain response and UTS of this class of composites. Second is the generalization of Curtin's model to include both process induced fiber bending and fracture. Third is that the reduction in strength is a sensitive function of the consolidation conditions; thus a link is established between the quality of the composite and the conditions of its manufacture.     

Interfacial reaction wetting in the boron nitride/molten aluminum system

An improved sessile drop technique which prevented the oxidation of aluminum was used to measure the changes in contact angle between boron nitride and molten aluminum in a purified He-3% H₂ between 1173 and 1373 K. The contact angle progressed through the four wetting phases similar to other ceramics when the results were plotted on a logarithmic time scale. However, at and above 1273 K the equilibrium contact angle was 0° which is much less than those of typical ceramics. Using the value in phase II, the original contact angle between boron nitride and aluminum (contact angle between non-reacted boron nitride and aluminum) was estimated to be 133° at 1373 K. The wetting progressed by producing another non-wetting material, AIN, in this non-wetting system. The detailed mechanism of the solid/liquid/vapor interfacial advance during wetting in such a system was also explained using Cassie's equation.