Liquid nitrogen strengths of coated optical glass fibres

The strengths of plastic-coated glass fibres have been measured at liquid nitrogen temperatures using a bending technique. The method yields data on the strengths of coated optical fibres in the absence of stress corrosion. Pristine strengths corresponding to a breaking strain of 21% have been measured for silica fibre and 12% for sodium borosilicate compound glass fibre, corrected to 50 cm gauge length. The low temperature strength was found to be directly related to the tensile strength measured at room temperature, and the relationship was valid for a variety of glass compositions with differing amounts of surface damage.     

Elastic-plastic and failure properties of a unidirectional carbon/PMR-15 composite at room and elevated temperatures

A series of off-axis tensile tests at room and elevated temperatures have been conducted up to 316°C (600°F) to determine the elastic and plastic properties of a unidirectional carbon/PMR15 composite as a function of temperature. The transverse tensile and shear strengths of the composite as a function of temperature have also been determined. The effect of the specimen preparation process (type of machining) on the strength properties of the composite has also been evaluated. It has been shown that elastic (with the exception of Poisson ratios ν₁₂ and ν₂₁), plastic, and strength properties of the composite are significantly affected by elevated temperatures. It has also been demonstrated that the quality of machining can noticeably influence the normal and shear strength data at room and elevated temperatures. Even if the quality of machining is very high, failure of the specimens can occur either in the gage or grip sections. At room temperature, all specimens failed in the grip areas influencing the transverse tensile and shear strength measurements. However, the type of specimen failure does not noticeably affect the strength data at elevated temperatures. The transverse tensile and shear strength properties of the composite at room temperature could only be estimated by extrapolating the normal and shear strength vs temperature curves to room temperature.     

Fractals in Steel-Aluminum Solid to Liquid Bonding

1.IntroductionSinceBenoitMandelbrotpresefltedfrartalthe-oryinhisbook<>inl977formally,itcanbesaidthatthestudyandapplicationoffractalshadbeencon-ductedinalmosteveryfieldgenerallyformorethan2oyears.On1yformetalfracturefield,greatevolutionandprogresshavebeenacquired,thegeneralrulesarethatalthoughthefracturesurfaceisscraggyandirreg-ular,ithasobviousselfanaloguecharacteristicwhenitisobservedwithinsomerealmofsize[1'2].There-foretheirregularityofthefracturesurfacecan…     

Study on Mechanical Property in Steel-Aluminum Solid to Liquid Bonding

The bonding of solid steel plate to liquid Al was conducted using rapid solidification.The influence of thickness of FeAl compound layer at the interface on interfacial shear strength of bonding plate was studied.The results show that the relationship between thickness of Fe-Al compound layer and interfacial shear strength is S=30.4 8.51 h-0.51h^2 0.007h^3(where h is thickness of Fe-Al compound layer,S is interfacial shear strength).When thickness of Fe-Al compound layer is 10.7μm,the largest interfacial shear strength is 71.6MPa。     

Effect of Relative Reduction on Property of Steel-Mushy Cu-Graphite Composite

The rolling treatment of steel-mushy QTi3.5-3.5 graphite composite was conducted under different relative reduction at room temperature. The effect of room-temperature rolling on interfacial mechanical property of steel-mushy QTi3.5-3.5 graphite composite was studied and the relationship between interfacial shear strength and relative reduction was established. The results show that, for steel-mushy QTi3.5-3.5 graphite composite, which consists of 1.2 mm-thick 08AI steel plate and 2.8 mm-thick QTi3.5-3.5 graphite layer, there is a nonlinear relationship between interfacial shear strength and relative reduction in graphite layer. When relative reduction is smaller than 1.1%, interfacial shear strength increases with increasing the relative reduction. When relative reduction is larger than 1.1%, interfacial shear strength decreases with increasing the relative reduction. When relative reduction is 1.1%, the largest interfacial shear strength of 145.2 MPa can be obtained.     

Influence of Rolling Treatment on Interfacial Shear Strength of Steel-mushy Al-7graphite Bonding Plate

At room temperature, the rolling treatment of steel-mushy Al-7graphite bonding plate was carried out under different relative reduction. The influence of rolling on interfacial mechanical property of this bonding plate was studied. The results show that, for steel-mushy Al-7graphite bonding plate which is made up of 1.2 mm in thickness 08AI steel plate and 2.0 mm in thickness Al-7graphite layer, there is a nonlinear relationship between interfacial shear strength of bonding plate and relative reduction of rolling. When relative reduction of rolling is smaller than 2.59%, with the increasing of relative reduction, interfacial shear strength of bonding plate increases gradually. When relative reduction of rolling is bigger than 2.59%, with the increasing of relative reduction, interfacial shear strength of bonding plate decreases continuously. When relative reduction of rolling is 2.59%, the largest interfacial shear strength 77.0 MPa can be obtained.     

Interfacial bond strength and fracture energy at room and elevated temperature in titanium matrix composites (SCS-6/Timetal 834)

Push-out experiments in the temperature range from room temperature to 530 °C have been performed. On the basis of the measured maximum load to break the fibre/matrix bond and the load to overcome frictional shear stresses finite element analyses are performed to derive an interfacial shear strength and interfacial fracture energy for the different test temperatures. The thus derived material properties decrease at increasing test temperature. In the analyses the in-homogeneity of the (shear) stress distribution plays an important role for the thermal as well as for the mechanical stress distribution. Although only the energy concept requires principally an initial debond length, it is shown that without an initial defect the shear strength concept leads to unrealistic results. The results presented are valid if it can be accepted that during specimen preparation an initial debonded zone of 12–18 μm at the surface is introduced.     

The adhesion of metal/alumina interfaces

Cylinders of copper and nickel have been melted under various conditions to form sessile drops on alumina plaques. The resultant metal/ceramic adhesion at room temperature has been measured using the commonly adopted test in which the drops are pushed off the ceramic plaques. The stress system involved in the test has been analysed and it has been shown that the standard interpretation of the test, as a measure of interfacial shear strength, is not valid; the revised interpretation makes it a measure of adhesion in tension. Results for the Cu/Al₂O₃ and Ni/Al₂O₃ systems show that non-wetted interfaces can be strong and have strengths that are independent of contact-angle changes caused by wetting-temperature variations.     

Thermomechanical behaviour of interfacial region in carbon fibre/epoxy composites

A study of the thermomechanical stability of the fibre-matrix interphase in carbon/epoxy composites has been carried out. The thermodynamic work of adhesion has been evaluated at room temperature by wetting measurements. The interfacial shear stress transfer level τ for sized and desized carbon fibre has been measured as a function of temperature by means of a single-fibre fragmentation test. As the test temperature increased τ values were found to decrease, with values being higher for the desized carbon fibre. The dependence of interfacial shear stress transfer on bulk matrix mechanical properties (modulus and shear strength) has also been discussed. Dynamic mechanical measurements performed on single-bundle composites confirmed the better thermomechanical stability of the desized fibre interphase.     

Mechanical properties of In-based eutectic alloy solders used in Josephson packaging

InBiSn and InSn eutectic alloy solders are used in the packaging of the cryogenic Josephson processor. The ductile behaviour of these alloys is important to the application of joints which experience large thermal stresses. In order to characterize the mechanical behaviour at cryogenic temperatures, tensile and shear strengths of bulk solders were measured at and below room temperature. It is found that the ultimate tensile and shear strengths of bulk solders increase as temperature decreases. At low temperatures, the ultimate tensile strength of InBiSn alloy is about three times less than that of InSn alloy. The ductility of both alloys reduces at low temperatures. The fracture surfaces of both bulk solders and solder joints having an interface material (Pd and Au thin films) to the electrical contact pads (Nb thin film) were examined using SEM. Ductile fracture mode was observed for all the specimens down to liquid nitrogen temperature.     

纳米SiO2对钢纤维/混凝土高温后力学性能及微观结构的影响

研究了掺纳米SiO₂的钢纤维混凝土(NSFC)、 钢纤维混凝土(SFRC)和普通混凝土(NC)三种材料在不同加热温度后的抗压、 劈裂和抗折强度等力学性能, 对不同温度热处理后的微观结构进行了SEM分析, 对钢纤维与过渡区界面的相结构进行了XRD分析。结果表明: 在测试温度范围内, NSFC的抗压、 劈裂和抗折强度均高于SFRC和NC的强度, 且在400 ℃时达到最大值。在常温下, NSFC的抗压、 劈裂和抗折强度较NC分别提高27.01%、 63.28%和54.12%, 400 ℃高温热处理后比NC分别高35.09%、 84.62%和87.23%; SEM分析表明, 在钢纤维与过渡区的界面处, 致密度提高, 显微硬度提高。由于固相反应, 使界面区结构发生变化, 在钢纤维表层形成扩散渗透层(白亮层), 即化合物层, 呈锯齿状, XRD分析证明, 白亮层主要由FeSi₂和复杂的水化硅酸钙组成, 从而增强了钢纤维与基体的粘结力, 提高了混凝土的高温力学性能。     

Mikrostrukturelle und röntgenographische Analysen an einem plasmanitrierten Schnellarbeitsstahl

Microstructural analysis of a plasmanitrided tool steel by means of metallography and X‐ray diffraction Nitriding leads to improved tribological and corrosive properties of iron alloy components. In order to study the effect of plasma nitriding parameters on the structure of compound layer and diffusion zone, a systematic variation of process parameters, temperature and process gas atmosphere has been carried out. Metallographic inspection, X‐ray diffraction and Glow Discharge Optical Spectroscopy analysis (GDOES) were used in this investigation. The results clarified that depending on the amount of nitrogen in the gas atmosphere nitrided layers with and without compound layer can be generated in the surface of M2 tool steel for temperatures from 350°C to 500°C. For plasma nitriding in 5 vol.% Nitrogen and 95 vol.% Hydrogen no compact compound layer was formed. The gas mixture of 76 vol.% Nitrogen resulted in compound layer formation for all temperatures from 350°C to 500°C. X‐ray phase analysis indicated an almost 100% ε‐(carbo)nitride phase but the existence of the γ′‐(carbo)nitride could not be excluded completely from the X‐ray phase diagrams. After corrections to account for the nitrogen gradient, high compressive surface residual stresses have been measured in the diffusion zone. They increased with temperature. After a qualitative correction for chemical composition gradients high tensile residual stresses were found probably existing in the ε‐(carbo)nitride phase for the investigated plasma nitrided tool steel samples.     

A study of the reactive brazing of a silicon nitride to steel using ternary Ag-Cu-Ti: microstructure and mechanical strength of the bonds

A study of the behaviour of Ag-Cu-Ti braze in contact with a ceramic - its wetta bility, evolution and reactivity-by different means of investigation gives some insight into the mechanisms involved in reactive brazing. Joints between siliconnitride and a structural steel were made by brazing under various conditions of temperature, hold time and a tmosphere. The room temperature mechanical strength measured in a shear test may be correlated to some microstructural and physicochemical features. The heterogeneous microstructure observed for almost all Ag-Cu-Ti brazes is explained by immiscibility in the liquid state with an equilibrium established between Ag-Cu-rich and Cu-Ti-rich liquids. It is shown that high temperatures (> 910°C) ensure a more efficient reaction of the titanium-rich phases and so a good wetting of the siliconnitride. Consequently, the shear strengths of bonds between siliconnit ride and steel achieved by using a sufficiently high brazing temperature are optimal (123-158 MPa).     

In-situ reactive synthesis of the Ni3Al intermetallic compound and subsequent diffusion bonding with different steels for surface coating

The Ni₃Al intermetallic compound has been in situ reaction synthesized from elemental powders to form a surface coating material and then diffusion bonded with three representative steels, i.e. a carbon steel, a stainless steel and a tool steel, in order to improve the high-temperature corrosion and wear resistance of these conventional materials. The as-reaction-formed intermetallic has been found to have an unstable crystalline structure. Diffusion-induced recrystallization takes place in the region close to the interface during subsequent diffusion bonding. A conformable contact between the as-reaction-formed intermetallic and the steel substrate is essential for subsequent interfacial bonding, which can be achieved by heating the as-reaction-formed intermetallic up to a high temperature to allow local melting to wet the interface prior to diffusion bonding. During diffusion bonding via an annealing step, an interdiffusion zone is formed and its thickness depends mainly on annealing temperature and duration. As a result of the microstructural development at the interface during annealing, different interfacial properties, i.e. a hardened interface or a softened one, can be obtained. The current success in coating the steels with the intermetallic opens up a new way to broaden the applications and prolong the service life of a wide range of conventional materials.     

Strengths and Fracture Mechanisms of Al2O3 Short Fiber Reinforced Al—Mg Alloy Matrix Composite at Elevated Temperatures

Using the experimental and theoretical methods,the tensile strengths and fracture mechanism of Al2O3 short fiber reinforced Al-Mg alloy matrix composite at elevated temperatures were researched.The interfacial microstructural characteristics and the fracture surfaces of the composite at different temperatures were observed by transmission electron microscope(TEM) and by scanning electron microscope(SEM) ,respectively.Then,from the results of microscopic observation,the fracture mechanisms of the composite at different temperatures are discussed.Finally, the tensile strengths of the composite at elevated temperatures were predicted by statistical integration average (SlA) method with the consideration of various fracture mechanisms.It was shown that the strengths and fracture mechanisms of the composite at elevated temperature (300℃) were significantly different from those at room temperature due to the variations of interfacial bonding states.The tensile strengths predicted by the SlA method at elevated temperatures agreed well with the experimental results.     

Very long-term aging of 52In–48Sn (at.%) solder joints on Cu-plated stainless steel substrates

Long-term metallurgical aging was studied in thermal switches comprised of 52In–48Sn (at.%) alloy solder plugs contained in Cu-plated stainless steel cylinders. These switches are locking devices designed so that, if overheated, a “fusible” alloy melts and allows the activation of a spring-loaded mechanism. The soldered assemblies studied ranged in age from about 24 to 28 years old at the time of this analysis. A concern has been the buildup of intermetallic compound (IMC) within the solder or at the solder/substrate interface, which could raise the switch operating temperature. In this work, the melting temperature of the aged solder alloy was slightly lower (116.3 ± 0.3 °C) than the expected value, 118.4 °C (245 °F), based on differential scanning calorimetry (DSC). The slight decrease in melting temperature range was caused by the diffusion of a small amount of Cu into the solder during processing and possibly during long-term service. The interfacial IMC layer was primarily Cu₂In₃Sn. The IMC thickness agreed with that predicted by growth kinetics determined in a previous study, assuming aging temperatures in the vicinity of room temperature. Differences in the IMC phase chemistries were found between earlier research, which employed bulk Cu substrates, and the present analyses with thin electroplated Cu substrates. Evidence was found for depletion of the thin Cu plating layer over time, as well as incorporation of Fe and Ni from the stainless steel into the IMC layer.     

Shear strength of polymers and fibre composites: 1. thermoplastic and thermoset polymers

The shear strengths of eight thermoplastics and three DGEBA-based epoxies in sheet form have been tested by the punch and Iosipescu tests. The testing temperatures ranged from 20 to 120°C, and the glass transition temperatures were measured as well. The shear strengths of the epoxies were also estimated from compressive tests on short cylinders. The Iosipescu test gave very unreliable results for polymers in the rubbery state because large deformations were induced before failure, and this caused high tensile stresses to develop instead of high shear stresses. With the punch test the force often had two maxima before failure, and the discs punched out did not have straight sides, so there was also much doubt about the purity of the shear stresses developed. The two methods were often in sharp disagreement. However, they gave comparable results with epoxies tested at room temperature. Comparison with compressive tests indicated that the ratio of compressive yield strength to shear yield strength varied from 1.5 to 2.4. In view of the uncertainties in the tests, compressive testing may be a good method to obtain an approximate value for the shear strength. The Tresca criterion (i.e. divide the compressive yield strength by two to get the shear yield strength) is probably good enough in view of the uncertainties in the shear tests. It works equally well for the ultimate shear strength. A new and better test is clearly needed for the estimation of the shear strength of polymers in sheet form.     

Bond shear modulus of reinforced concrete at high temperatures

The effect of fire and high temperature on the behavior and properties of concrete has drawn considerable attention. In this work an experimental program is used to determine the effect of high temperature on the interfacial bond shear modulus between concrete and reinforcement. Steel bars of different diameters were embedded in concrete cylinders for a depth less than that required for total development to assure failure by loss of bond. Specimens were then kept in an oven for different time durations and different temperatures. Specimens were then cooled by either keeping cylinders at room temperature or immersing them in water. The pull-out test was applied, and loads and displacements were recorded. Results from the pull-out test were then used along with an analytical model to calculate the bond shear modulus. The analytical model is based on the physical representation of the pull-out test, assuming linear elastic behavior of both steel and concrete.     

Structure-sensitive properties during room-temperature wire drawing at various speeds in nickel 200

The effects of drawing speed, cell size and grain size on the yield strength of nickel 200 wires drawn at room temperature up to a true strain of 2.09 have been investigated. The wire drawing speeds in the range from 17 to 140 mm s^–1 do not show any effect on the yield strength, cell size and grain size of drawn wires. However, the cell sizes as well as grain sizes decrease with increase in true wire drawing strain when their values are averaged over all the wire drawing speeds at a given strain. Even though the Hall-Petch equation is valid for all the grain diameters observed in this study, the graph suggests that two distinct linear regimes may be more appropriate to properly describe the strengthening mechanisms during wire drawing. The cell diameter has been correlated with the yield strengths of drawn wires by an inverse relationship.     

The effect of hydrostatic pressure on the fibre-matrix bond in a steel-resin model composite

The shear strength of the adhesive bond between a steel wire and an epoxy resin has been measured and it has been found that when the composite is under pressure the strength corresponds closely to the shear yield stress of the resin determined in a plane strain compression test. Discrepancies at low pressure may be due to the nucleation of stress-concentrating cracks. Measurements of the friction stress between the wire and the resin as a function of pressure indicated that the coefficient of friction was 0·5 and that the compressive stress at the interface due to resin shrinkage was 7 Nmm^–2 (1000 psi).