Tensile properties of partially austenitised and austempered ductile irons with dual matrix structures

Abstract

In the present study, an unalloyed ductile iron containing Fe–3·50C–2·63Si–0·318Mn–0.047Mg (wt-%) were intercritically austenitised (partially austenitised) in two phase region α+γ at various temperatures of 795, 805, 815 and 830°C for 20 min and then quenched into salt bath held at austempering temperature of 365°C for various times to obtain different ausferrite volume fractions (AFVFs). Results showed that dual matrix structure containing proeutectoid ferrite, new ferrite (also called epitaxial ferrite) and ausferrite (bainitic ferrite+high carbon austenite, which is retained or stabilised austenite) has been developed. Within each of the austempered series in α+γ temperature range, new ferrite volume fraction increased with increasing intercritical austenitising temperature (ICAT). Although, transforming percentage of new ferrite from parent austenite present at ICAT increased with decreasing ICAT. Some specimens were also conventionally austempered from 900°C for comparison. The new ferrite was absent in these samples. The volume fraction of proeutectoid ferrite, new ferrite and ausferrite can be controlled to determine the strength and ductility. Austempered specimens in α+γ temperature range exhibited much greater ductility than conventionally austempered ones. The tensile strength increased while ductility decreased with increasing AFVF. On the other hand, the ductility increased with increasing proeutectoid ferrite and new ferrite volume fractions at the expense of strength. The specimen with ～47·2%AFVF exhibited the best combination of high strength and ductility. The strength and ductility of this material is much higher than that of ferritic grades. Its strength is at the same level as while ductility almost more than four times higher than that of pearlitic grades. Meanwhile, the specimen with ～ 75%AFVF exhibited the best combination of high strength and ductility compared with those of pearlitic grades. The strength of this material is much higher and its ductility is almost more than two times higher than that of pearlitic grades yet slightly lower than that of ferritic grades. This material also meets the requirements for the strength of quenched and tempered grades and its ductility is higher than that of this grade.     

Tensile properties of directionally solidified Al-Al3Ni composites with off-eutectic compositions

Ingots (1/8 in. diameter) of Al-Al₃Ni with off-eutectic compositions were directionally solidified at two growth rates. At 1 cm h^–1 fibres exhibited a blade-like morphology, and at 11 cm h^–1, a rod-like morphology. Speciments were mechanically evaluated in tension. The composite modulus at stresses above the yield strength of the aluminium matrix obeyed the rule of mixtures, assuming ideal plastic behaviour of the matrix. An extrapolation of these data for composites with rod fibres gave a value of 146 GN m^–2 for the modulus of Al₃Ni. Tensile strength of composites with rod-like fibres followed the rule of mixtures, whereas those with non-uniform blade fibres showed a lower strength. In composites with blade-like fibres the extrapolated aluminium matrix strength was 86.3 MN m^–2, a high value attributed to dispersion hardening, and that of the fibres was 2.69 GN m^–2. Composites with blade-like fibres failed at lower strains than did those with more uniform rod-like fibres.     

Tensile fracture properties of an Ultra High Performance Fiber Reinforced Concrete (UHPFRC) with steel fiber

This paper presents a study of the tensile fracture properties of Ultra High Performance Fiber Reinforced Concrete (UHPFRC) considering the effects of the fiber content. To investigate the impact of fiber content, notched 3-point bending tests were executed, where the fiber volume ratio was varied from 0% to 5%. From the bending tests, it was found that the flexural tensile strength of UHPFRC linearly increases with increasing fiber volume ratio and the rule of mixture can be applied to UHPFRC. Furthermore, an inverse analysis was performed to determine the tensile fracture model of UHPFRC and a tri-linear tensile softening model is suggested. The suggested model successfully represents the increase of the stress-constant bridging zone and the decrease of the stress-resisting zone with increasing fiber content. The proposed model for various fiber content levels is simple and versatile and can be readily applied to structural design or numerical analysis of UHPFRC.     

Tensile behaviour of multi-layered braided structures

Multi-layered braided structures are formed as a result of over-braiding the previously formed braids and they are increasingly being used for numerous applications ranging from hoses to energy absorbing composites. In this research work, a series of multi-layered braided structures were prepared on circular braiding machine for obtaining various combinations of braid angles of 30° and 45° in inner and outer layers. Subsequently, the tensile properties of multi-layered braided structures were analysed and it was found that the braid angle in the outer layer has significantly affected the stress–strain behaviour. A simple analytical model for predicting the tensile behaviour of multi-layered braided structures has also been proposed based on the previously developed model of ‘braid-elastic core’ system. A clear distinction has also been made between the helix and braid angles. Furthermore, a comparison has been made between theoretical and experimental values of braid angle, toughness and stress–strain characteristics of multi-layered braided structures.     

Tensile behaviour of nonwoven structures: comparison with experimental results

Nonwoven structures have been recently explored for numerous novel applications ranging from composites to scaffolds. The tensile property of nonwovens is a pre-requisite and indeed, one of the main parameters to determine their performance for such applications. In the first part, a modified micromechanical model describing the tensile behaviour of thermally bonded nonwovens was proposed by incorporating the effect of fibre re-orientation during the deformation (Rawal et al., J Mater Sci 45:2274, 2010). In this study, an attempt has been made to compare the theoretical and experimental stress–strain curves of thermally bonded and spunbonded nonwoven structures. These theoretical findings have been obtained from the most popular analytical tensile models of nonwovens available in the literature in addition to our modified tensile model. Poisson’s ratio has also been determined experimentally in order to predict the stress–strain behaviour of nonwoven, and its relationship with longitudinal strain has clearly distinguished between the randomly and preferentially orientated types of structures. In thermally bonded nonwovens, the tensile strength in various test directions is computed through pull-out stress and a comparison is made with the experimental results.     

3钉带衬套复合材料/金属接头拉伸疲劳性能

带衬套沉头螺栓连接已经在复合材料连接结构中得到了一定应用,需要对其疲劳性能进行研究.本工作在单搭接 3 钉带衬套碳纤维复合材料/钛合金沉头螺栓连接接头实验研究基础上,建立复合材料及金属结构的疲劳分析模型,对结构的疲劳性能进行有限元分析,并与无衬套接头模型进行对比,研究衬套对接头疲劳性能的影响.结果表明,使用衬套比仅采用螺杆过盈装配能够更加有效地提升接头的疲劳寿命,其中层合板寿命提高了约 3 .6 倍,钛合金板寿命提高了约 2 .7 倍,螺栓寿命提升了约 1 4 倍,并且仅出现钛合金板破坏,紧固件不破坏.结合实验结果分析发现,由于复合材料和金属材料自身疲劳性能的差异,其机械连接结构的疲劳破坏模式会因载荷水平的不同而发生变化;当载荷水平较低时,金属结构更容易发生破坏.     

Vibration damping properties of steel/rubber/composite hybrid structures

By using hybrid structures, attractive and advantageous combinations of material properties can be achieved. In addition to the combination of good mechanical properties and low weight, also dynamical properties can be enhanced by suitable materials selection. However, the hybrid structure properties depend on the properties of the constituent materials as well as on the interfacial properties.     

Tensile properties of jute fibres

Abstract

One hundred tensile tests were undertaken at each of five distinct fibre lengths (6, 10, 20, 30 and 50 mm) on a single batch of jute fibres from South Asia. The Young's moduli were found to be independent of length. The ultimate stress (fracture strength) and fracture strains were found to decrease with increasing fibre length. The variation in mechanical properties at each fibre length was characterised using Weibull statistics based on a maximum likelihood estimate; referred to as point estimates. Two empirical based models (a linear and a natural logarithmic interpolation model) have been developed to estimate the fracture properties at any length between 6 and 50 mm. These two interpolation models were also developed based on maximum likelihood estimates. The point estimates were used to benchmark the performance of the two models. The natural logarithmic model was found to be superior to the linear model.     

Tensile properties of a few Mg-Li-Zn alloy thin sheets

The tensile properties of experimentally produced Mg-6Li-1Zn, Mg-9.5Li-1Zn and Mg-12Li-1Zn alloy thin sheets at room temperature are investigated in this study. Uniaxial tension tests are carried out for various strain rates between 1.4 × 10^–5 and 8.3 × 10^–2 s^–1, and the microstructural and textural changes during the tests are examined. The Mg-6Li-1Zn sheet is composed mainly of the (hcp) phase and inferior to the other sheets in ductility. The (bcc) phase is dominant in the Mg-9.5Li-1Zn and Mg-12Li-1Zn sheets, and they have a considerable sensitivity to strain rate. It is observed that the grains are elongated with textural change mainly in the phase at low strain rates, and the Mg-9.5Li-1Zn and Mg-12Li-1Zn sheets have sufficiently high ductility at low strain rates. The Mg-9.5Li-1Zn sheet composed of ( + ) two phase is superior to the Mg-12Li-1Zn sheet of single phase in the tensile strength.     

Magnetic properties of solid solutions between BiCrO3 and BiGaO3 with perovskite structures

Magnetic properties of BiCr_1−xGa_xO₃ perovskite-type solid solutions are reported, and a magnetic phase diagram is established. As-synthesized BiCrO₃ and BiCr_0.9Ga_0.1O₃ crystallize in a monoclinic (m) C2/c structure. The Néel temperature (T_N) decreases from 111 K in BiCrO₃ to 98 K in BiCr_0.9Ga_0.1O₃, and spin-reorientation transition temperature increases from 72 K in BiCrO₃ to 83 K in BiCr_0.9Ga_0.1O₃. o-BiCr_0.9Ga_0.1O₃ with a PbZrO₃-type orthorhombic structure is obtained by heating m-BiCr_0.9Ga_0.1O₃ up to 573 K in air; it shows similar magnetic properties with those of m-BiCr_0.9Ga_0.1O₃. T_N of BiCr_0.8Ga_0.2O₃ is 81 K, and T_N of BiCr_0.7Ga_0.3O₃ is 63 K. Samples with x = 0.4, 0.5, 0.6 and 0.7 crystallize in a polar R3c structure. Long-range antiferromagnetic order with weak ferromagnetism is observed below T_N = 56 K in BiCr_0.6Ga_0.4O₃, T_N = 36 K in BiCr_0.5Ga_0.5O₃ and T_N = 18 K in BiCr_0.4Ga_0.6O₃. BiCr_0.3Ga_0.7O₃ shows a paramagnetic behaviour because the Cr concentration is below the percolation threshold of 31%.     

18.8%MnTRIP/TWIP钢拉伸应变硬化行为

对锰含量为18.8%的TRIP/TwIP钢进行单轴拉伸实验,研究了这种钢的应变硬化行为.结果表明:这种高锰TRIP/TWIP钢的真应力应变曲线不完全遵循Holliomon的线性关系,在不同变形阶段强化机制不同.在塑性变形的开始阶段TRIP效应比较明显,且应变硬化指数n是恒定的;而真应变在O.14-0.35之间时二阶导数d2σ/dε2>0,应变硬化指数n随着应变量的增加而增加,其微观机制是形成大量的形变孪晶,并有孪晶和位错的交互作用,TWIP效应在该阶段占主导作用.真应变大于0.35后有少量TRIP效应,此时两相均发生变形.     

Tensile,fracture toughness and crack growth properties of a roll-extruded HP 9Ni-4Co-25C steel alloy

A section of internal roll-extruded HP 9Ni-4Co-25C steel alloy was obtained from an experimental 120-in. rocket motor case for Titan III and sent to the Air Force Materials Laboratory for evaluation by the Space and Missile System Organization (SAMSO). Tensile and fracture toughness properties were obtained at room temperature and at ?65°F. Crack growth properties were obtained at room temperature in laboratory air and in distilled water. An increase in tensile strength and a decrease in ductility were observed to occur with increased cold forming reduction. Fracture toughness properties appeared to decrease with increased rolling reduction. Fatigue crack growth properties in laboratory air were compatible with other high strength steels for the lower ΔK values. Fatigue crack growth properties in distilled water showed no acceleration due to aqueous environment influences. Statically loaded stress corrosion crack (SCC) growth properties were an improvement over available D6ac steel alloy data.     

Tensile properties of flow-formed polypropylene pipe

The effects of varying the percentage reduction on the tensile properties of flow-formed polypropylene pipes were investigated. Flow-forming, which is a single-point cold rolling process, was performed by using two rollers in a single pass on a conventional lathe machine. Specimens were cut at different orientation angles to the pipe direction. The load-extension behaviour of the flow-formed material showed that the phenomena of yielding and cold drawing gradually become less prominent above 30% reduction. These phenomena were also functions of the orientation angle. From the variations of tensile properties with orientation angle, it was concluded that flow-forming can produce high anisotropy, especially above 30% reduction. Improvements in yield and tensile strength were achieved after about 35 to 45% reduction. The tensile modulus increased significantly after 50% reduction. The yield strain reaches a maximum at about 50 to 60% reduction. Elongation at break decreases with increased reduction. It was noted that 80% reduction appeared to be the maximum reduction, after which the material will exhibit extremely low ductility.     

Tensile properties of metastable stainless steels

Tensile properties of two similar stainless steels, types 301 and 304, were investigated for different strain-rates, grain sizes and testing temperatures, and the bulk concentration of martensite formed during deformation was determined by X-ray diffraction.Results show that type 301 has a distinct strain-peak on the elongation/temperature curve, and strains up to 1.2 were obtained; type 304 steel exhibits only a shallow peak in the elongation/temperature curve. The course of the formation of strain-induced martensite was found to be similar in the two steels at low temperatures (0 to 20°C) but significantly different at higher temperatures. It is shown that it is not the amount of martensite that is the major factor in obtaining large elongations to failure, but rather its formation, which must be both gradual and selective. It is proposed that the first requirement is dependent on temperature and structural details, while the later requirement is governed by the parameter (– dM/dT), the temperature sensitivity of the resistance to martensite formation.     

Tensile properties of open-cell nickel foams

Open-cell nickel foams with average pore size of 600 μm have been subjected to room temperature tensile tests to explore their tensile properties. Using a state of the art extensometer of non-contact type, foam properties as ultimate tensile strength (UTS), yield strength (YS) and the Young’s modulus (E) have been measured accurately. An extensometer of non-contact type was applied for the first time to help the foam’s mechanical properties to be determined accurately. The reason behind the usage of this kind of extensometer is to avoid completely any minor deformation that might be caused by the attachment of conventional extensometer to the sample’s surface prior to testing. The function of this extensometer is based on the usage of a laser (CCD) camera that detects and records the dimensional changes as soon as the load is applied. The fracture behavior of foam cells was observed to be ductile. Complete separation of struts or cell walls took place successively by necking.     

Tensile properties of a bone cement containing non-ionic contrast media

The addition of contrast media such as BaSO4 or ZrO2 to bone cement has adverse effects in joint replacements, including third body wear and particle-induced bone resorption. Ground PMMA containing particles of the non-ionic water-soluble iodine-based X-ray contrast media, iohexol (IHX) and iodixanol (IDX), has, in bone tissue culture, shown less bone resorption than commercial cements. These water-soluble non-ceramic contrast media may change the mechanical properties of acrylic bone cement. The static mechanical properties of bone cement containing either IHX or IDX have been investigated. There was no significant difference in ultimate stress between Palacos R (with 15.0 wt % of ZrO2) and plain cement with 8.0 wt % of IHX or IDX with mass median diameter (MMD) of 15.0 or 16.0 microm, while strain to failure was higher for the latter (p < 0.02). The larger particles (15.0 or 16.0 microm) gave significantly higher (p < 0.001) ultimate tensile strengths and strains to failure than smaller sizes (2.4 or 3.6 microm). Decreasing the amount of IHX from 10.0 wt % to 6.0 wt % gave a higher ultimate tensile strength (p < 0.001) and strain to failure (p < 0.02). Scanning electron microscopy (SEM) showed the smaller contrast media particles attached to the surface of the polymer beads, which may prevent areas of the acrylate bead surface from participating in the polymerization. In conclusion, the mechanical properties of bone cement were influenced by the size and amount of contrast medium particles. By choosing the appropriate amount and size of particles of water-soluble non-ionic contrast media the mechanical properties of the new radio-opaque bone cement can be optimized, thus reaching and surpassing given regulatory standards.