Distortion of nylon 6,6 moldings caused by asymmetric water absorption

Distortion of nylon 6,6 molded bars caused by one-sided absorption of water has been investigated experimentally and the results have been compared with the predictions of an analysis based on data measured on dry bars or bars that were immersed completely in water. Account is taken of swelling, secondary crystallization, variations in Young's modulus, and the original residual stress distribution prior to the absorption of water. The major influences on distortion are (i) swelling and (ii) secondary crystallization. A much smaller effect is caused by the change in the residual stress distribution resulting from the change in the distribution of Young's modulus that develops when water is absorbed. The two major effects normally act in opposite directions, and may sometimes balance out. Differences in distortion obtained when moldings that had different aging histories were exposed to water absorption from one surface only are discussed.     

Effect of pore clustering on the mechanical properties of ceramics

The reduction in strength and, to a lesser extent, Young's modulus with increased amounts of discrete pores is frequently greater than that predicted by models based on a homogenous pore distribution. The effect of pore distribution has been examined in the present work by producing samples containing a non-homogenous distribution of pores and comparing the results with data reported for samples containing homogenously distributed pores. Young's modulus and, to a greater extent, strength were shown to have stronger dependencies on the porosity content than would be predicted for homogeneous samples. By considering the material as a composite consisting of a pore-rich continuous phase containing a dispersion of pore-free material, various models were used to predict behaviour. It was found that the strength of the material is likely to be governed by the properties of the continuous phase, while the Young's modulus is a function of the properties of the two phases, with the porous phase being described by the Spriggs equation. The implications of the different dependencies of strength and Young's modulus in terms of the resistance to crack propagation following a thermal shock were then considered. Predictions of retained strength were in good agreement with those observed after water quenching.     

Young's Modulus of Elasticity of Carbon‐Bonded Alumina Materials up to 1450°C

Investigating Young's modulus at elevated temperatures supports the understanding of microstructural changes as a function of application temperature. A sintered alumina and three carbon‐bonded alumina materials with carbon contents of 20 and 30 wt% and alumina grain size of 0.6–3 mm were investigated. Young's modulus was measured in a temperature range from 25°C to 1450°C by the impulse excitation technique. The Young's modulus of carbon‐bonded materials increases up to 140% at 1450°C. After one cycle, a decrease of the Young's modulus up to 50% is registered at room temperature. There is a strong hysteresis behavior during one cycle. Thermal expansion measurements show highest expansion for the highest graphite content material. The expansion of alumina grains and graphite flakes, resulting in microcrack generation during cooling and microcrack healing during heating, is reflected in the registered values of the Young's modulus as a function of the temperature. It is assumed, that higher graphite amounts as well as coarse grains lead to lower sintering effects of the microstructure at elevated temperatures and as a result lower values of the Young's modulus have been registered.     

The dependence of the elastic properties of silica/alumina materials on the conditions used for firing

The dependence of the elastic properties of a range of powder compact samples has been measured as a function of firing variables. It was found that both Young's modulus and Poisson's ratio are particularly sensitive to the peak temperature and the time for which the peak temperature is maintained, over a range of these variables for which density is not significantly affected. The material investigated is used industrially for the manufacture of wall tiles. Firing trials conducted in an industrially operated tunnel kiln have indicated that sufficient variation in firing conditions exists, in the cross-section of the tunnel kiln, to cause significant variation in the values of Young's modulus and Poisson's ratio of bodies fired in different positions in the kiln. Microstructural examination of bodies produced to have very similar densities but vastly different values of Young's modulus and Poisson's ratio has indicated that the dependence of Young's modulus and Poisson's ratio on firing conditions can be explained by the extent of sintering within the ceramic matrix.     

Compilation of mechanical properties for the structural analysis of solid oxide fuel cell stacks. Constitutive materials of anode-supported cells

The mechanical failure of one cell is sufficient to lead to the end of service of a solid oxide fuel cell (SOFC) stack. Therefore, there is growing interest in gaining knowledge on the mechanical properties of the cell materials for stress analysis.This study compiles available data from the literature on the mechanical properties of the most common materials used in intermediate-temperature anode-supported cells: nickel and yttria-stabilized zirconia (Ni–YSZ) anodes, YSZ electrolytes, yttria (YDC) or gadolinia-doped ceria (GDC) compatibility layers and lanthanum strontium manganite (LSM) or lanthanum strontium cobalt ferrite (LSCF) cathodes. The properties for the simulation of stresses, i.e. coefficient of thermal expansion (CTE), Young's modulus, Poisson's ratio, creep behaviour and strength are reported, with an emphasis on temperature and porosity dependence and the evolution upon aging or cycling when available. Measurements of our Ni(O)–YSZ anode material includes the CTE (oxidised and reduced state), Young's modulus and strength at room temperature (oxidised and reduced) and 1073 K (oxidised).     

Mechanical studies on poly(vinylidene fluoride) based polymer electrolytes

The mechanical strength of the poly(vinylidene fluoride) (PVDF) based polymer electrolyte deteriorates with increasing salt content. For a salt concentration of 2 wt% the Young's modulus is 10^?5 Pa. The Young's modulus reduces by 60% when the salt concentration increases five‐fold. The decrease in mechanical strength of the polymer electrolyte by the incorporation of the salt is attributed to the intramolecular interaction between the chains of the polymer and the salt. The mechanical strength of the polymer electrolyte was also analyzed for different plasticizer content. The plasticizer used was ethylene carbonate (EC). The Young's modulus of the plasticized polymer electrolyte decreased with increased in EC content, but the elongation of the material and the energy at break increased with EC content, showing increased flexibility.     

Processing–mechanical property relationships in injection moldings of polybutylene

Two unfilled nonpigmented extrusion grades of polybutylene have been injection-molded into a tensile bar mold under a wide range of barrel and mold temperatures. The overall structure of the moldings has been determined and correlated with processing conditions. The short term tensile mechanical properties of the moldings have been ascertained and correlated with molding structure. For low mold temperatures, the Young's modulus and tensile strength of injection moldings of polybutylene are controlled by the extent of and structure within the highly oriented skin. Low barrel temperatures can give rise to highly crystalline thick skins that treble the Young's modulus and fracture stress, when compared to high barrel temperature moldings. Increasing the mold temperature introduces a brittle response in polybutylene injection moldings. Modulus is controlled, at the high mold temperatures, by the skin thickness and by the crystallinity of the material comprising the core of the molding.     

Young's modulus of isotropic porous materials with spheroidal pores

Based on the Eshelby solution for the single-inclusion problem and Wu's specification of this solution to spheroidal pores, we show that the Eshelby–Wu coefficients for Young's modulus, in contrast to their counterparts for the bulk and shear moduli, are quite insensitive to changes of the Poisson ratio. Therefore the Eshelby–Wu coefficients of Young's modulus can be described (to a very good approximation) by a unique function of the aspect ratio, which is calculated in this paper and for which a master curve is obtained by segment-wise fitting. Also the implementation of the Eshelby–Wu coefficients into the well-known effective medium approximations (Maxwell, self-consistent, differential) and our exponential relation is discussed. Irrespective of the model into which the Eshelby–Wu coefficients are implemented, prolate pore shape affects the porosity dependence of Young's modulus only very weakly, whereas oblate pore shape can lead to an arbitrary reduction of Young's modulus.     

The amorphous contribution to the modulus of a semi-crystalline polymer

The amorphous contribution to the Young's modulus of a semi-crystalline polymer is calculated for two morphologies: the spherulite and the stacked lamellae structure. Four types of amorphous chains are considered: bridges (or tie molecules); cilia; loops; and floating, unattached chains. The statistics of a polymer chain between two, infinite, impenetrable, parallel walls are used in the modulus calculation. It is found that for each type of amorphous chain, the Young's modulus is greater in the stacked lamellae structure than in the spherulite. The Young's modulus of a cilium, loop and floating chain all increase with increasing chain contour length while the Young's modulus of a bridge passes through a minimum value. The behavior of the Young's modulus as a function of temperature is analogous. These results are discussed in terms of the relative importance of crystalline lamellar impenetrability and the inherent elastic nature of the amorphous chains, in the Young's modulus behavior.     

Fiber orientation control of short‐fiber reinforced thermoplastics by ram extrusion

In this study we examine the fiber orientation distribution, fiber length and Young's modulus of extruded short‐fiber reinforced thermoplastics such as polypropylene. Axial orientation distributions are presented to illustrate the influence of extrusion ratio on the orientation state of the fibrous phase. Fibers are markedly aligned parallel to the extrusion direction with increasing extrusion ratio. The orientation state of extruded fiber‐reinforced thermoplastics (FRTP) is almost uniform throughout the section. The control of fiber orientation can be easily achieved by means of ram extrusion. Experimental results are also presented for Young's modulus of extruded FRTP in the extrusion direction. Young's modulus follows a linear trend with increasing extrusion ratio because the degree of the molecular orientation and the fiber orientation increases. The model proposed by Cox, and Fukuda and Kawada describes the effect of fiber length and orientation on Young's modulus. The value of the orientation coefficient is calculated by assuming a rectangular orientation distribution and calculating the fiber distribution limit angle given by orientation parameters. By comparing the predicted Young's modulus with experimental results, the validity of the model is elucidated. The mean fiber length linearly decreases with increasing extrusion ratio because of fiber breakage due to plastic deformation. There is a small effect on Young's modulus due to fiber breakage by ram extrusion.     

Tensile behaviour of magnesia carbon refractories

The determination of the Young's modulus and the tensile strength of heterogeneous refractories are the subjects of this paper. Great differences have been observed for a similar material according to both the usual tests performed and the interpretation proposed to define these properties. The causes of the discrepancies of the Young's modulus under compression and tensile loading are examined in detail. Then, it is shown that (i) the accuracy measurement of the deflexion in the bend test with a particular device and (ii) the integration of the shearing distorsion in the calculation of the deflexion by the classical beam theory, allow for finding the appropriate value of the Young's modulus. The classical definition of the modulus of rupture (M.O.R.) is also examined. Considering a nonlinear behaviour of the refractory, it is shown by finite element analysis of the beam, that the M.O.R. overestimates the tensile strength.     

Unveiling the environment-dependent mechanical properties of porous polypropylene separators

Porous polypropylene (PP) is commonly used as separator materials for lithium ion batteries (LIB). Its mechanical properties, especially critical for abuse tolerance and durability of LIB, are subject to change in different environments. To capture the mechanical responses of a porous PP separator, its microstructure was mapped into separate atomistic models of bulk crystalline phases and oriented amorphous nanofibers. These structures were relaxed and stretched in vacuum, water, and dimethyl carbonate (DMC) using molecular dynamics (MD). The simulation results revealed DMC molecules penetrated into the amorphous PP nanofiber, and reduced the local density and the Young's modulus. In contrast, water increased the Young's modulus of the amorphous PP nanofiber. Furthermore, neither water nor DMC had any impact on the Young's modulus of the crystalline phase. These results suggest that the DMC induced separator softening was attributed to the strong attraction of the less-polar DMC solvent with the amorphous fibrous PP nanofibers.     

Measurement of in‐plane elastic moduli of composites with a circular disk specimen and piezoelectric sensors

Many test specimen configurations and test methods have been used for measuring the in‐plane elastic constants of orthotropic composites. While the measurement of the Young's modulus is straightforward, the shear modulus determination is more difficult. Most of the experimental methods require more than one specimen for the measurement of all the in‐plane elastic constants. In the proposed method, a single test specimen in the form of a circular disk is sufficient. The Young's modulus and the shear modulus are measured with piezoelectric sensors that produce and detect dilatational and shear waves, respectively. The experimental techniques involved and the possible methods of interpreting the results are explained. The results obtained were compared with those determined for bar specimens of the same material, using piezoelectric sensors and strain gauges. The comparisons are encouraging. POLYM. COMPOS., 26:542–551, 2005. © 2005 Society of Plastics Engineers     

Analysis of the mechanical properties of TiN/Ti multilayer coatings using indentation under a broad load range

In this study, physical vapor deposition was used to prepare TiN/Ti multilayer coatings as well as the corresponding monolithic coatings for comparison. Nanoindentation using a large load range (5–4800 mN) and finite element method (FEM) simulations were conducted to investigate the influence of various multilayer structures on the mechanical behavior of multilayer coatings. The nanoindentation results show that the TiN/Ti multilayer coating has the maximum hardness and Young's modulus while retaining good crack resistance and fracture toughness. The FEM results show that increasing the number of layers in the multilayer coatings reduced the hardness and Young's modulus as well as the maximum stress, while it increased the equivalent plastic strain. As the layer thickness ratio increased, both the hardness and Young's modulus gradually increased, and the stress in the coating reached its maximum at the highest thickness ratio. In addition, to consider the effect of the indentation depth on the coating, the influence of the number of layers and the layer thickness ratio on the multilayer coating is combined into the indentation response of the multilayer coating. Therefore, we establish an expression describing the relationship between the number of layers and the ratio of the layer thickness to the mechanical properties of TiN/Ti multilayer coatings.     

Using polystyrene spheres to produce thin,porous interlayers in alumina laminates

Porous alumina layers were produced by colloidal processing of alumina with the addition of 15, 30, and 45 vol% polystyrene spheres (PS) as pore formers. Alumina laminates were designed with dense layers alternated with porous interlayers using 45 vol% of PS spheres and sintered at 1350°C. The layers’ thickness ranged from 2 to 15 μm, with a random distribution of pores. The higher volume fraction of pores tends to decrease the alumina average grain size, but does not influence the final size of bulk and surface pores. The obtained values of hardness and Young's modulus for the porous interlayer are ∼30% of the values obtained for the dense layer. Vickers indentations suggested that crack propagation can be opposed by the porous interlayers. However, values of mechanical strength, fracture toughness (K_IC), and work of fracture presented no relevant difference compared to a monolithic reference. R-curves presented a slight increase and K_IC a decrease due to crack propagation through the porous interlayers. Although no macrodeviations of the crack path were observed in the fractured surfaces, microdeviations were detected in the interlayer regions.     

Structure and properties of nanocomposites prepared by directly melt blending ethylene‐co‐vinylacetate and natural montmorillonite

The poly(ethylene‐co‐vinylacetate)/montmorillonite (EVA/MMT) nanocomposites were prepared by directly melt blending EVA and natural MMT in the presence of hexadecyl trimethylammonium bromide. The interlayer spacing of the silicate layers in EVA/MMT nanocomposites increased within 15 min of the blending time, and then remained unchanged with further increase in the blending time. The tensile and tear strength and Young's modulus of EVA/MMT nanocomposites increased with increasing blending time and reached the maximum value at 15 min, and then decreased. The tensile and tear strength and Young's modulus of EVA/MMT nanocomposites blended at 140°C were lower than those of the nanocomposites blended at 120°C. The thermal stability of EVA/MMT nanocomposites was improved compared with EVA. Furthermore, the thermal stability of EVA/MMT nanocomposites in nitrogen was higher than thermal stability of the nanocomposites in air because of the air destabilized the EVA and speeded up both deacylation and degradation. POLYM. COMPOS., 27:529–532, 2006. © 2006 Society of Plastics Engineers     

Influence of the mechanical behaviour specificities of damaged refractory castables on the Young's modulus determination

This paper deals with the problematic of the determination of the Young's modulus of refractory castables by the way of mechanical tests. Two materials are considered: a cordierite based refractory castable that is reinforced with short steel fibres and an andalusite based refractory castable. Discrepancies in Young's modulus values are noticed depending on whether they are determined on direct tensile test curves, four points bending test curves or compression test curves. Damage due to a first thermal cycle is underlined as enhancing these discrepancies. Original mechanical tests have been performed in order to understand the influence of such a damage on the four points bending and compression behaviours. Results show that depending on the method that is used to measure displacements and strains, the calculated Young's modulus values can be highly influenced by local strain effects that occur at the contact between the sample and the loading system. Related to the damage that develops in these materials during the first heat treatment, these effects are more important when samples have been previously fired.     

The determination of the axial Young's modulus of honeycomb specimens under bending

For solid specimens, Young's modulus is commonly determined from straightforward uniaxial tension experiments. However, honeycomb specimens are far more challenging to test in tension, and it is therefore desirable to conduct bending experiments to determine Young's modulus. The premise of this work is that the bending response of honeycomb specimens may be significantly different from that of solid specimens, and therefore it is necessary to establish a sound protocol for the determination of the axial Young's modulus of honeycomb specimens under bending. Toward this goal, we present results of a study that combines experimental, finite element simulation, and classical beam theory approaches. These results confirm that accurate measurements of Young's modulus of honeycombs require careful consideration of the specimen geometry and analysis of the data. We demonstrate that the use of conventional Bernoulli‐Euler's beam theory to interpret the data requires very slender specimens. We also show that less slender specimens can be used if the experimental data is interpreted on the basis of three‐dimensional elasticity theory and numerical simulations. A third option is to use a combination of moderately slender specimens and Timoshenko's beam theory.     

Relationship between Young's modulus and temperature in porcelain tiles

A focused research was conducted on samples prepared from an industrial porcelain tile composition containing quartz, used to produce ceramic floor tiles, with the aim of evaluating the variation of fired specimens’ Young's modulus with temperature. These samples were fired in controlled laboratory conditions so that specimens with pre-existing cracks were obtained and subject to non-destructive in situ thermo-mechanical measurements (impulse excitation technique) in the 22–700 °C temperature range during heating and cooling processes in order to find evidences to explain the hysteresis phenomenon in the Young's modulus versus temperature curve. The observed irreversible Young's modulus may be directly related to the pre-existent cracks that on heating and cooling are closed and opened up respectively, changing thus the Young's modulus which is well characterized by a hysteresis cycle.     

Elastoplastic finite element stress analysis and strength evaluation of adhesive lap joints of hollow shafts subjected to tensile loads

The stress distributions in adhesive lap joints of dissimilar hollow shafts subjected to tensile loads have been analyzed by the elastoplastic finite element method, taking the nonlinear behaviors of the adhesive and the hollow shafts into consideration. A prediction method for the joint strength has been proposed based on the Mises equivalent stress distribution in the adhesive and the frictional resistance between the adhesive and the shaft after rupture of the adhesive. In the experiments, three different kinds of adhesive lap joints were made, i.e. the inner and outer hollow shafts were aluminum alloy/aluminum alloy, steel/steel, and steel/aluminum alloy combinations, and the tensile strength of each joint was measured. From the numerical calculations, in the case of the two hollow shafts made of the same material, the tensile strength increases with an increase of Young's modulus of the shaft and in the case of the two hollow shafts made of different materials, the tensile strength increases when the inner hollow shaft of larger Young's modulus is bonded to the outer one of smaller Young's modulus. Also, the effects of the overlap length and the inner diameter of the inner shaft on the tensile strength of the joint are discussed. By comparing the predicted values of the tensile strength with the experimental results, it was shown that the proposed prediction method could estimate the tensile strength of the adhesive lap joints of hollow shafts within an error of about 15%.