Influence of heat treatment processes on fatigue performance of particle reinforced aluminium alloys

Abstract

The fatigue performance of particle reinforced metal matrix composites improves as the matrix strength is increased. However, the heat treatment required for high matrix strength induces residual stresses into the material, which need to be balanced against potential distortion during machining of components. This paper reports results showing the fatigue behaviour of a 2124 aluminium alloy reinforced with 25 vol.-% of silicon carbide particles. The effect of quench medium on tensile and rotating bend fatigue strength is reported. Results are correlated with residual stress profiles measured in quenched plates of the material.     

Influence of Erroneous Data on the Results of Calculations From Acid–Base Surface Free Energy Theories. III. Solution of a Three-Equation Set in the Case of Homoscedastic Error

The van Oss–Chaudhury–Good theory (vOCGT) was checked for a large artificial set of work of adhesion input data calculated for 15 solids and 300 liquids. Numerical values of LW component and acid (A) and base (B) parameters were assigned to 15 solids. These 15 solids were grouped in 5 sets of 3 solids in each. Also numerical values of LW component and A and B parameters were assigned to 300 liquids (three sets of 100 liquids in each). Data for these solids and liquids were especially selected to represent real types of materials encountered in practice. For all 15 solids and 300 liquids the work of adhesion values were calculated and these values were assumed to be error-free. Next, new values of the work of adhesion were obtained by adding a random homoscedastic error (A vector of random variables is homoscedastic if it has the same finite variance.) of the normal distribution (Also called the Gaussian distribution — it is continuous probability distribution defined by two parameters: the mean and variance (standard deviation squared, σ ²).), belonging to 8 distributions of a mean value equal to the error-free work of adhesion value and standard deviations of 0.5, 1, 2, 5, 7, 10, 15 and 20 mJ/m². The LW components and A and B parameters for these solids were back-calculated for each error level. Two different methods for the solution of a 3-equation set were used and they gave practically the same results irrespective of the error level and liquids and solids used. It was found that there existed a linear correlation between the RMSE (root mean square error) of the solution and the standard deviation of the work of adhesion data. This correlation was highly significant (with a correlation coefficient higher than 0.999) and was true separately for LW component, A and B parameters as well as for the total solution vector (i.e., combinedly for the LW component, A and B parameters). The RMSE values of the total solution vector (having as elements values of the LW component, A and B parameters) as well as separately for LW component and A and B parameters were correlated with the condition number of a given 3-equation set. A very good correlation was found only for the total solution, much worse for A or B parameters, and practically there was a lack of correlation for the LW component. Based on the correlation between the RMSE and the standard deviation of the work of adhesion it was possible to determine what should have been the maximal standard deviation of the work of adhesion if the calculated value of a given LW component or A or B parameter did not differ by more than 1 mJ/m² from an error-free (true) value.     

33—THE SNARLING OF HIGHLY TWISTED MONOFILAMENTS. PART II: CYLINDRICAL SNARLING

An account is given of an experimental investigation of the cylindrical snarling of highly twisted monofilaments.

The theory underlying cylindrical snarling is set out, and an expression is derived for calculating the critical twist level at which normal snarling will be replaced by cylindrical snarling. Experiments on rubber filaments are described, and it is shown that there is good agreement between the theoretical and experimental results. Further experiments, in which the specimen was allowed to contract freely or forced into other forms, are also described.

It is shown from these experiments that it is difficult to establish the true equilibrium behaviour, since the situation appears to be dominated by frictional effects or by direct barriers to relative movement.     

Effect of heating rate on dielectric and pyroelectric properties of double doped PZT

Abstract

Double doped lead zirconium titanate (PZT) was synthesised by solid state reaction method. Calcination and sintering was carried out at various heating rates in order to study the effect of heating rate on the extent of phase formation of double doped PZT. Furthermore, the effect of heating rate on dielectric and pyroelectric properties was also investigated. Rhombohedral perovskite phase was confirmed in the double doped PZT samples. Quantitative X-ray diffraction (XRD) analysis suggests that the extent of PZT formation decreases beyond 8°C min^?1 heating rate. The crystallite and grain sizes calculated from Scherrer's equation and field emission scanning electron microscope (FE-SEM) photographs respectively show the decreasing behaviour with increasing heating rate. Dielectric and pyroelectric properties show the increasing behaviour up to 8°C min^?1 and decreasing behaviour beyond this heating rate.     

1st Mediterranean Conference on Heat Treatment and Surface Engineering

Abstract

Energy and the environment are not only receiving mass public attention, but are also indisputably the main drivers for the development of present day scientific, industrial, economic and social progress. However, anyone attempting to review these topics faces two huge problems: the overwhelming volume of often conflicting information and the rapidly evolving national, international and global situation. Thus, the survey presented here, with heat treatment and surface engineering in mind, is a selection of ideas, discussion material and data that is designed to trigger focused discussion and substantive contributions.     

32—THE SNARLING OF HIGHLY TWISTED MONOFILAMENTS. PART I: THE LOAD–ELONGATION BEHAVIOUR WITH NORMAL SNARLING

An account is given of an experimental investigation of the normal snarling of highly twisted monofilaments, those used being vulcanized rubber and nylon.

An earlier theoretical analysis is corrected, and the experimental results show that, after this correction, the theory put forward for the mechanical properties of the snarling mechanism holds reasonably well for elastic filaments. Although, as would be expected, there are larger deviations from the theory for viscoelastic filaments, the theory still gives a good indication of the behaviour of these filaments under torsion.     

Effects in Surface Free Energy of Sputter-Deposited VNx Films

Vanadium nitride (VN _x ) thin films have attracted much attention for semiconductor integrated circuit (IC) packaging molding dies, and forming tools due to their excellent hardness and, thermal stability. VN _x thin films with VN_0.45, VN_0.83, VN_1.22, VN_1.73, VN_2.06 were prepared using a radio frequency (RF) sputter technique. The experimental results showed that the contact angle at 20°C increases with increasing nitrogen content of the VN _x films, to 101.4° corresponding to VN_1.73 and then decreased. In addition, the contact angles decreased with increasing surface temperature, because an increase of the surface temperature disrupts the hydrogen bonds between water and the films and the water gradually vaporizes. The total surface fee energy (SFE) at 20°C decreased with nitrogen content of the VN _x films to 29.8 mN/m (VN_1.73) and then increased. This is because a larger contact angle means weaker hydrogen bonding which results in a lower SFE. The polar SFE component had the same trend as the total SFE, but the dispersive SFE component had the opposite trend. The polar SFE component is also lower than the dispersive SFE component. This is because hydrogen bonds are polar. The total SFE, dispersive SFE and polar SFE of the VN _x films all decrease with increasing surface temperature. This is because with increasing temperature, water evaporates from the surface, disrupting hydrogen bonds and hence increasing surface entropy. The film roughness has an obvious effect on the SFE and there is tendency for the SFE to increase with increasing film surface roughness. As a result the SFE and surface roughness can be expressed in terms of a simple ratio function.     

Effect of the surface roughness of sulfuric acid-anodized aluminum mold on the interfacial crystallization behavior of isotactic polypropylene

The influence of the surface topography of aluminum alloy (Al) on the heterogeneous nucleation of isotactic polypropylene (iPP) at the iPP/Al interface has been investigated using a polarized optical microscope (POM) with a hot stage. Different textures of the Al surface were prepared by electrochemical processes, including polishing and anodizing, and utilized to induce interfacial nucleation upon supercooling. This process enabled the topological features of the aluminum surface to be controlled without altering their chemical composition by such a procedure. The pretreated surfaces were investigated by scanning electron microscopy and quantitatively characterized by a surface texture instrument in terms of RMS roughness (R _a). The Al surface with a higher surface roughness induced more nuclei of iPP and led to a transcrystalline layer (TCL) in the interfacial region upon supercooling over the temperature range 128°C < T _c < 154°C. Based on the theory of heterogeneous nucleation, it was found that the induction time correlates well with the nucleation rate in determining the interfacial free energy difference function Δσ of iPP. The ratio of Δσ at the interface to that in the bulk matrix (ΔσTCL/Δσ _bulk) for the polished surface (R _a = 0.38 μm) is 4.45, implying that transcrystallization growth is unfavorable from a thermodynamic point of view. On the other hand, the Δσ _TCL/Δσ _bulk ratio decreases as the current density for anodizing increases, indicating that transcrystallization growth becomes favorable. The induction times and nucleation rates were also measured to characterize quantitatively the nucleating ability of various Al surfaces. The oxide porosity was filled in when sealing treatment by hydration was carried out. This resulted in Δσ _TCL/Δσ _bulk being slightly higher as the surface roughness decreased.     

The Do's and Don'ts of Wettability Characterization in Textiles

Surface treatments introduce chemical modifications to the fiber surface that affect the surface free energy (SFE). This is done either with the obvious aim to change the wetting behavior, or to affect related properties, such as, e.g., adhesion phenomenon, surface conductivity, adsorption of proteins, etc. On planar substrates, the measurement of contact angles of specific liquids and making use of formalisms such as Neumann or Owens–Wendt equations is a commonly used approach to determine the surface free energy. It is to be observed that this direct approach is often and lightheartedly applied to porous and textured samples, such as textiles, too. The geometry of a textile is extremely complex and defined by the topography of the fiber, the construction of the yarn, and the construction of the fabric. In addition, polymer fibers may be porous and take up water from the environment. Accordingly, wetting is the result of simultaneous spreading on a rough surface, penetration, and capillary motion in the multi-porous system. Therefore, the critical consideration of any analytical method for wettability measurements cannot be overemphasized, and the present paper is meant to critically discuss the pros and cons of various methods common to the textile researcher. It can be summarized that contact angles can be useful for comparative measurements on hydrophobic samples, while the established drop penetration tests characterize the effects of fabric finishing, fiber surface modifications, etc. with limited quantification. By no means can these test be used to derive the SFE, and in all cases it is essential to avoid accidental distortions of the fabric. The single fiber micro-Wilhelmy method can be regarded as the only reliable method to obtain advancing and receding contact angles.     

Influence of the interfacial resin layer on delamination initiation in broken ply composite laminates

The present study has investigated the influence of a resin layer on the delamination initiation at the interface of broken and continuous plies in the case of GR/E (graphite/epoxy) laminates with broken central plies. A full three-dimensional (3D) finite element (FE) analysis was performed with each layer of the laminate modelled as homogeneous and orthotropic. The interface between the broken and the continuous plies was modelled with a thin resin-rich layer. Eight-noded isoparametric layered elements were used to model the laminate specimen. Also, 3D contact elements were used to prevent inter-penetration of the delaminated faces at the interface. Based on the results of the 3D FE analysis, strain energy release rates were calculated at the delamination front using Irwin's 'crack closure integral'. Using the concepts of linear elastic fracture mechanics (LEFM), the strain energy release rate was used as a parameter for assessing delamination initiation. The effects of various factors such as resin layer stiffness, resin layer thickness, and fibre orientation at the interface on the three components of the strain energy release rates, namely G_I, G_II and G_III, were studied for laminates with various crack sizes of the broken ply, and the influence of the resin layer in the delamination initiation was established. It was observed that delamination initiation is a mixed-mode phenomenon even in the case of uniaxial loading and the dominance of the mode of delamination is governed by the resin layer stiffness, thickness, and lamina orientation at the interface. The present work also concludes that an increase in the resin layer modulus leads to an increase in the probability of mode I delamination while the probability of mode II delamination decreases. A 0/90 interface exhibits a higher chance of delamination in modes I and II, while mode III delamination is maximum for 0/30 and 0/60 fibre orientation interfaces. It was also observed that the larger the crack width, the greater the probability of delamination initiation at the interface.