Effect of preparation conditions on relative elongation of nickel foam

Abstract

The effect of preparation conditions on the relative elongation of nickel foams prepared by electrodeposition technology has been studied. The relative elongation is hardly influenced by sintering in NH₃ decomposition atmosphere at 980°C for 40 min, by burning in air at 600°C for 4 min beforehand, or by lowering the sintering temperature to 850°C. With regard to conductive treatment, the relative elongation is significantly higher for chemically plated Ni than for coating by graphite base conductive colloid.     

超声波对泡沫镍抗拉强度和延伸率的影响

针对导电胶法制造泡沫镍存在的抗拉强度、延伸率低，结果不均匀等问题，在制造泡沫镍的浸涂石墨导电胶和电沉积镍的过程中，首次采用超声波发生装置，对比研究了有无超声波的4种情况下制得泡沫镍的抗拉强度、延伸率及三维网络结构。结果表明：超声波增加了石墨导电胶在泡沫基体上浸涂的均匀性；大大提高了镍在石墨导电层上初期沉积和后期沉积的均匀性；增大了Ni的结晶过电位，使Ni的临界晶核半径变小，结晶更加致密；泡沫镍的三维网络结构更加均匀，抗拉强度、延伸率大大提高。在自行设计制造的生产线上，验证了本文的试验结果。     

Relationship between tensile strength and porosity for foamed metals under equal speed biaxial tension

Abstract

A preliminary experimental investigation has been carried out on an isotropic three dimensional reticulated foamed metal with high porosity under biaxial tensile loading. The approximate relationship between tensile strength of these materials and their porosity has been evaluated under equal-speed biaxial tension loading. The mathematical formula is proved to be in a good agreement with the experimental data for nickel foam.     

Relationship between degassing conditions and tensile properties of Al-20Si-X P/M products

Results are reported which show the effect of different degassing modes on the properties of the Al-20Si-3Cu-1 Mg powder. The paper complements previous papers [1–3] concerning the conventional and modified degassing of the same powder. This research was mainly directed to study the influence of temperature on the tensile properties, ultimate tensile strength, σ_UTS, and elongation, ɛ, of extrudates obtained of Al-20Si-3Cu-1Mg compacts non-degassed, conventionally degassed, and treated by a modified process, namely degassing assisted by flushing with a depurative gas such as argon or nitrogen. The processing of the Al-20Si-3Cu-1Mg P/M powder must include a degassing step which significantly improves the tensile properties, at room and elevated temperatures, of the products of compacted powder with respect to those of the products whose compacts were non-degassed. It is apparent that degassing assisted by flushing with argon or nitrogen gives products with higher tensile properties than those of the products conventionally degassed under optimal conditions of temperature and time and much higher than those of the non-degassed products. The tensile results are in agreement with the theoretical approach to the gas entrapment and evolution of the aluminium powders presented in previous papers.     

Influence of mix proportions and curing conditions on tensile splitting strength of high strength concretes

The effect of the composition of high strength concretes with low water to binder ratio and silica fume on the development of splitting tensile strength was studied. A statistical approach was employed to develop formulation which could adequately describe the relations between splitting tensile strength and the concrete composition, when cured in two different regimes: water curing at 20°C and sealed curing at 30°C. Autogenous shrinkage was induced in the second type of curing but was largely eliminated in the first one. The relations were presented as nomograms which could be used as a basis for mix design. The correlation between tensile splitting strength and compressive strength could not be described in terms of a simple linear relation with a characteristic constant. For the range of variables studied, the ratio between tensile and compressive strength varied over a large range of 0.08 to 0.12. As a result, the relations developed here for tensile strength are quite different in nature than those for compressive strength in a previous study. Analysis of the data suggest that tensile strength is sensitive to effects which induce autogenous shrinkage to a much greater extent than compressive strength. It is proposed that this may be the main reason for the different trends observed for the relations between the composition of the low water/binder ratio concretes and their compressive and tensile strength.     

A general relation between tensile strength and specimen geometry for concrete-like materials

The tensile strength of concrete-like materials varies wiries when different test procedures or even different shapes and sizes of specimens are employed. Correlations have previously been established but restricted to particular test conditions. The approach here presented, based on the “weakest link of the chain” concepts, offers the possibility of correlating the results of the different tensile tests of concrete-like materials. For that purpose, the amount of material under a tensile stress greater than 0.95 of the maximum tensile stress in the specimen must be evaluated. Relating the maximum tensile stress at the moment of failure with the above mentioned volume (Highly Stressed Volume), a decreasing function is obtained. The function fitted can be used to obtain a tensile strength value of the material, free from the influence of the characteristics of tests and specimens. In this experimental work, the function is established by testing seven different mortar mixes, subjected to nine different test conditions. Centered-point and third-point loading flexural tests and splitting tests were carried out on specimens of different sizes. Direct tension on a briquertte was also applied. The test results showed a decreasing linear regression between the logarithm of the maximum tensile stress at the moment of failure and the logarithm of the highly stressed volume. The slope of that line remained fairly constant for the seven mortar mixes tested.     

Interrelations between creep and slow crack growth for tensile loading conditions

Phenomenological interrelations between creep strain and slow crack growth are derived based on the fact that the total creep strain at fracture is determined by the growth kinetics of a pre-existing crack. It is shown that measurements of the creep strain in a region remote from the growing crack can be used to predict failure periods for materials that concurrently exhibit creep and slow crack growth.

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Résumé En se basant sur le fait que la déformation totale de fluage lors de la rupture résulte d'une cinétique de croissance d'une fissure préexistante, on établit les interrelations phénoménologiques entre la déformation de fluage et la croissance lente d'une fissure. On montre que des mesures de la déformation de fluage dans une région éloignée de celle où croît la fissure peuvent être utilisée pour prédire les temps de rupture de matériaux qui peuvent présenter simultanément du fluage et de la croissance lente d'une fissure.

     

Testing and modeling for the tensile strength of nylon badminton string at different processing conditions

Nylon is a thermoplastic engineering material widely used in several applications. But to increase the application of nylon in sports, the focus of this work was to optimize the tensile strength of nylon for badminton string. In particular, the testing conditions (temperature, relative humidity and tensile rate) were investigated. The results obtained showed that increasing the processing temperature and humidity both had a negative effect on tensile strength, while increasing the tensile rate had a positive effect. Then, a mathematical model to predict the tensile strength was established by using a response surface methodology and the optimal conditions were verified to validate the parameters. Furthermore, an analysis of variance was used to determine the significant effect of each term on the final response. Based on the results obtained, it was found that the optimum processing temperature is 2.9 °C with a relative humidity of 0 % when the tensile rate is 60 mm/min.     

Relationship between seal strength and burst pressure for pouches

Based on force analysis, the seal strength obtained from the peel test is equivalent to the product of the burst pressure and half of the plate separation obtained from the burst test. To verify this relationship peel tests and burst tests were performed using MRE pouches. Good agreement between the observed and predicted values was observed when the peeling times of the two tests were the same. This relationship is useful for comparing the performance of the two tests, as well as for establishing criteria for destructive and non-destructive testing.     

制备条件对炭泡沫结构的影响

利用沥青在热解过程中产生挥发性气体自发泡和高压渗氮的原理，以石油中间相沥青为原料，采用高压反应釜制备炭泡沫材料。用SEM和偏光显微镜观察了材料的孔结构，分析了制备条件对炭泡沫结构的影响。结果表明，温度和压力是影响炭泡沫材料结构的重要因素，在实验条件范围内，较高的反应温度和压力有利于制备出较高性能的炭泡沫，其气孔率较高，韧带炭层排布规则。     

Models for strength prediction of foam concrete

There are several strength prediction relations developed for plain cement paste, mortar and concrete. In concrete where air voids contribute significantly to volume of voids (like aerated and foam concrete), more general expressions including the volume of air voids is to be developed as the better alternative. The objective of this paper is to propose prediction relations for the compressive strength of foam concrete by extending two of the well-known relations available for cement paste, mortar and normal concrete, viz., Balshin’s strength-porosity model and Power’s gel-space ratio equation. For this, theoretical equations were derived for porosity and gel-space ratio relating it to the density, proportion of ingredients in the mix and material characteristics like specific gravity. Foam concrete with fly ash showed lesser dependency on pore parameters than cement-sand mixes. As both the prediction relations developed in this study consider the effect of composition on the strength, it can serve as a simple tool for predicting the strength of foam concrete. But strength-porosity model stands out compared to gel-space model as it correlates well with the measured strength and also because of its ease in application since it employs the composition of constituents and easily measurable parameters.     

Preparation and corresponding structure of nickel foam

Abstract

A nickel foam with a three-dimensional reticulated structure has been prepared by an electrodeposition technique. The microcrystalline structure of the nickel layer was maintained following treatment in air at 600°C for 4 min. Sintering in a reductive decomposed NH₃ atmosphere for 40 min, at either 980 or 850°C, transformed the product into a compact nickel crystal with a flat surface and large crystal grains.     

Interaction between tensile strength failure and mixed mode crack propagation in concrete

Crack size and structure size transitions are illustrated which connect the two limit-cases of ultimate tensile strength failure (small cracks and small structures) and mixed-mode crack propagation (large cracks and large structures). The problem of mixed-mode crack propagation in concrete is then faced. By increasing the size-scale of the element the influences of heterogeneity and cohesive crack tip forces disappear and crack branching is governed only by the linear elastic stress-singularity in the crack tip region. It is proved in this way that the fracture toughness of the material is measured by a unique parameter (G_IF, G_IC or K_IC) even for the mixed-mode condition. The ratio of the sliding or Mode II fracture toughness (G_IIF, G_IIC or K_IIC) to the opening or Mode I fracture toughness depends only on the crack branching criterion adopted and not on the material features. Eventually, very controversial experimental results recently obtained on the shear fracture of concrete are explained on the basis of the above-mentioned size-scale transition.     

Correlation between structure and compressive strength in a reticulated glass-reinforced hydroxyapatite foam

Glass-reinforced hydroxyapatite (HA) foams were produced using reticulated foam technology using a polyurethane template with two different pore size distributions. The mechanical properties were evaluated and the structure analyzed through density measurements, image analysis, X-ray diffraction (XRD) and scanning electron microscopy (SEM). For the mechanical properties, the use of a glass significantly improved the ultimate compressive strength (UCS) as did the use of a second coating. All the samples tested showed the classic three regions characteristic of an elastic brittle foam. From the density measurements, after application of a correction to compensate for the closed porosity, the bulk and apparent density showed a 1 : 1 correlation. When relative bulk density was plotted against UCS, a non-linear relationship was found characteristic of an isotropic open celled material. It was found by image analysis that the pore size distribution did not change and there was no degradation of the macrostructure when replicating the ceramic from the initial polyurethane template during processing. However, the pore size distributions did shift to a lower size by about 0.5 mm due to the firing process. The ceramic foams were found to exhibit mechanical properties typical of isotropic open cellular foams.     

化学电源用泡沫镍的性能研究

作为化学电源的一种重要的电极基体材料,泡沫镍的机械特性和电学特性不仅直接影响到电池极板的综合性能,而且与电池大规模工业化生产的可行性及经济性直接相关.泡沫镍的性能参数包括各向异性、厚度、面密度、镍丝体结构、孔率、孔形等直接影响上述特性.在实际生产中可通过对泡沫基材的选择和生产过程优化控制这些参数.本文根据化学电源对基体材料机械特性和电学特性的要求,结合电池的制造工艺对泡沫镍在化学电源领域的应用进行了专题研究.     

Combined experimental and theoretical method of determining strength characteristics of materials under quasistatic tensile conditions

The article presents a combined experimental and theoretical method of determining strength characteristics of materials in high-speed tensile tests on specimens with shortened gauge length in which there is no region of uniaxial state of stress. Numerically, by the finite element method, zones of nonuniaxial state of stress over the gauge length of the specimen are established.Translated from Problemy Prochnosti, No. 9, pp. 26–28, September, 1991.