Experimental unit for determining the fracture-toughness characteristics of materials

An experimental unit is proposed for determining fracture-toughness characteristics in the starting, movement, and stopping of a crack under static, cyclic, and impact loading. A basically new method of securing and loading the specimen is employed in the unit. The method significantly reduces the amount of elastic energy accumulated in the machine-specimen system and improves the “purity” of the experiment by having the specimen acted upon only by a disjoining force. Also, the working element (wedge) provides only an initial impulse at the stage of crack initiation, stops in a predetermined position, and then functions as a transducer recording the force that develops in the specimen over time. Tests can be conducted on DCB (double cantilever beam), CT (compact), and CB (concentrated bending) specimens. Translated from Problemy Prochnosti, No. 1, pp. 139–144, January–February, 1997.     

Quantitative analysis of prediction models for hot cracking in industrial stainless steels using standardized requirements

In this paper, a systematic analysis of different methods of δ-ferrite estimation is carried out based on the well-known relationship between δ-ferrite content and hot cracking in stainless steels. Additionally, the influence of certain chemical requirements on δ-ferrite stabilization and their relationship to hot cracking is evaluated by the application of a deterministic algorithm based on stringency levels. The results obtained from the application of the stringency level method and prediction diagrams permit the selection of the best option among materials according to their standardized specifications. In addition, the advantage of this integrated method is that we can evaluate particular elemental influences and assign relative weightings to create a database for materials selection.     

Development of a copper-based filler alloy for brazing stainless steels

The filler alloy of nominal composition Cu–40Mn–10Ni (all in wt%) was prepared in the form of ribbon of 40 μm thick by melt spinning technique. The ribbon exhibits narrow melting zone and comprise single phase of Cu–Mn–Ni solid solution. The melt spun ribbon successfully brazed 304 stainless steel butt joints. The formation of solid solution in the joining area without any intermetallics is observed. The bonding strength of filler alloy is achieved around 456 MPa.     

Development of silver-base alloy for crown and bridge prostheses

Three silver-base alloys containing varying amounts of tin and copper were prepared by induction melting and centrifugal casting, and their properties were evaluated and compared with those of the type III gold alloy, for their suitability for non-porcelain crown and bridge work in dentistry. Among these the alloy II (Ag–Sn–Cu–Zn) was found to possess the best combination of strength and ductility and highest corrosion resistance in artificial saliva. Also its wear resistance was found superior to alloys I and III and was comparable to that of natural tooth. Thus the alloy II was found to be quite a promising indigenous and economic silver-based cast alloy for crown and bridge prostheses.     

高速铁路桥面用聚氨酯防水涂料

以聚醚多元醇和甲苯二异氰酸酯(TDI)制备预聚体,自制扩链剂混配芳香胺为固化剂,制备了一种配比为1∶1的双组份聚氨酯防水涂料。其特征技术指标达到拉伸强度11MPa,断裂伸长率600%,撕裂强度55N/mm,与混凝土粘结强度4.0MPa,可以满足《客运专线桥梁混凝土桥面防水层暂行技术条件》中对聚氨酯防水涂料的要求。     

Development of engineering requirements for unified software facilities for metrological purposes

We present a new approach to specification of requirements for software for metrological purposes; the basis for the approach is the GOST R/ISO/IEC 9126-93 standard. We present practical formulas and results of requirement specifications for simple characteristics. Translated from Izmeritel'naya Tekhnika, No. 6, pp. 11–14, June, 1998.     

Numerical simulations of fracture-toughness improvement using short shaped head ductile fibers

Fibers can be shaped so as to anchor inside the matrix and resist pullout at a crack face, thus improving the fracture-toughness of the composites. This anchoring ability enables a greatly improved utilization of the plastic potential of ductile fibers, increasing fracture-toughness while maintaining stiffness. The purpose of this paper is to explore this property of shaped head fibers for composites with weak fiber–matrix bonding. Because of the difficulty in estimating the fracture-toughness contribution of shaped head fibers analytically or experimentally, we use a FEM based numerical scheme to investigate stress profiles induced during pullout of two chosen shaped head families. Annealed copper fiber with a large residual plastic potential and an elastic epoxy matrix have been used as representative materials. Using the computed strain energy distribution in the matrix as a measure of fracture-toughness contribution, we find that flat-head fibers out-perform ball-head fibers in minimizing failure potential. We have further discovered that within each shape family there exist optimal shapes. The optimal shape for the flat-head family is also computed for the example material system.     

Development of robust processing routes for powder metallurgy high speed steels

Abstract

This paper reviews progress made in understanding the factors which control the supersolidus liquid phase sintering of high speed steel powders to full density. The correlation between alloy composition and sintering behaviour is discussed for a number of alloy systems. Realising that for complete densification it is necessary for sintering to take place in the liquid +γ+M₆C+MC (or MX) phase region, two approaches have been developed to extend this critical phase field. This enables a scientific development of alloys that are more robust to process variations than currently sintered high speed steels of standard (for wrought materials) compositions. The new alloy systems possess wider process or sintering windows and have lower optimum sintering temperatures. The first approach relies on computer aided alloy design: vacuum sintering windows extending to 30–40 K at temperatures of 1170–1200°C have been achieved for novel Fe–C–4Cr–14Mo(–8Co)systems. The second approach involves sintering vanadium enriched high speed steels (HSSs) in nitrogen rich atmospheres. Such processing promotes the formation of MX carbonitrides in place of the more massive MC carbides. The solidus is lowered and sintering windows of ～30 K at temperatures of 1140–1150°C have been achieved. Compared with wrought HSSs, directly sintered materials have uniform, coarser microstructures. The low levels of residual porosity achieved enable attainment of metal and wood cutting properties comparable to those achieved with wrought and hipped HSSs of similar compositions.     

Development and study of an automatic AC bridge for impedancemeasurement

An automatic ac bridge method employing the principle of balancing by means of a stochastic gradient search algorithm is presented. Among the various gradient search techniques, the Widrow-Hoff least mean square (LMS) technique has been chosen as it involves a low computational burden. The LMS algorithm has been used by the authors for the operation of an ac bridge operating with continuous variables. The relevant operation has been verified by simulation; it can also measure negative impedance. A relation has been established between parameters to be used in the LMS algorithm for discrete and continuous versions of the bridge. The balance convergence time for a relatively simple form of the LMS bridge, namely, the R-R type bridge, has been theoretically established and experimentally verified both by simulation and real-time implementation. The frequency response of the LMS algorithm has also been determined     

高性能节约型不锈钢制备技术研发与应用

开发了409L和410S铁素体不锈钢冷轧板的淬火-配分(QP)工艺,获得了铁素体、马氏体和残余奥氏体的复相组织。通过优化奥氏化温度、淬火温度和配分时间,获得了尽量多的马氏体和残余奥氏体。与常规退火和淬火-回火(QT)工艺相比,QP工艺获得了最优的强度和延伸率组合、连续性屈服和适中的n值、r值,达到了高强度和易成型的要求,能够替代先进高强钢用于生产汽车结构件。     

Development of structural steels with re resistant microstructures

Abstract

This paper is concerned with the design and characterisation of fire resistant steels for building construction. Steel design considerations are discussed. Issues raised include controlling the grain size, properties of substitutional elements, and processing. New experimental fire resistant steels microalloyed with molybdenum and niobium, or tungsten, titanium, and boron have been made and their microstructures and tensile properties characterised. The steels possess satisfactory high temperature strength, owing partly to their relatively large grain sizes compared with conventional steels. The nature of equilibrium precipitation has been calculated using Thermo Calc. Optical microscopy, SEM, TEM, and differential scanning calorimetry have been used to determine the physical characteristics. The strengthening mechanisms observed on the experimental steels of this study could be attributed to secondary formation of fine precipitates, in line with previous observations.     

Development of 3rd generation Medium Mn duplex steels for automotive applications

The mechanical behaviour and fracture were studied in a Fe–5Mn–2.5Al–0.2C (in wt-%) Medium Mn steel. Metallographic and magnetic measurements confirm the significant influence of the transformation kinetics of the strain-induced martensite on the mechanical properties and strain heterogeneities (Lüders and Portevin-Le Chatelier-like phenomena). An accurate study of isothermal evolutions of the microstructure, associated with atomistic calculations, complements current thermodynamic databases to quantify the nature and volume fraction of phases at different temperatures. A kinetic approach then predicts the influence of annealing conditions on the composition of retained austenite, key parameter for the martensitic transformation kinetics. This supports quantitative modelling of the influence of the intercritical annealing temperature on the ultimate tensile strength for industrial developments of these new grades.     

Development of a new methodology for estimating the CTOD of structural steels using the small punch test

The small punch test (SPT) is very convenient for estimating tensile mechanical properties, being the estimation of fracture toughness still a controversial subject of debate. One of the new strategies developed is the use of notched specimens. In this paper, two different grades of CrMoV steels were employed to analyse the evolution of the notch mouth opening displacement of the small punch sample (δSPT). Complete and interrupted tests were performed on specimens with longitudinal non-through notches with a notch length to thickness ratio of 0.3. A numerical model was also developed for corroborating the experimental results. A material-independent relationship between δ_SPT and the punch displacement (d) was found: δ_SPT = 0.217d. Since crack length measurement is not possible on SPT samples, the value of δ_SPT at crack growth onset (δ_{SPT_ini}) was used for comparison with the CTOD values for crack initiation in the standard tests (δ_ini). Crack growth onset in the SPT specimens was verified by observation after splitting them in two halves, as well as comparing the numerical curves (without damage model) and the experimental ones. Larger values have been obtained by means of the SPT, due to the lower constraint of the test. However, the developed methodology seems to be suitable when dealing with ductile steels, although other different materials are needed to be tested.     

Development of bridge tooling for fabricating mold inserts of aspheric optical lens

A bridge tooling is developed for fabricating the temporary mold inserts of aspheric lens using silicone rubber materials. Prototype material of the aspheric lens is not recommended as quartz due to low successful rate in the fabrication process. This technology provides a fast, low cost, and high successful rate for fabricating the epoxy‐based composites mold inserts of plastic aspheric optical lens.     

Prediction of the probability of nonfailure of structural elements of heat-and-power-generating equipment from the fracture-toughness characteristics of the material

Conclusions A method was developed to predict the life of important structural elements of heat-and-power-generating equipment from the parameter of the probability of nonfailure on the basis of statistical modeling of the vector of random parameters of crack-resistance characteristics of the metal using criteria of linear fracture mechanics.We also developed an algorithm and a program which automate the computing process with the use of modern computers to predict the life of a structure from the crack resistance of the material in a probabilistic formulation.We will subsequently conduct studies involving the construction and substantiation of the representativeness of samples of mechanical tests of materials for crack resistance, which is very important in predicting the safe life of a structure.Institute of Strength Problems, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Problemy Prochnosti, No. 1, pp. 7–13, January, 1987.