Investigation of the effect of diffusion bonding parameters on microstructure and mechanical properties of 7075 aluminium alloy

In the present study, diffusion bonding of aluminium alloy (AA7075) sheet materials which are used especially in the automobile and aerospace industry has been investigated at temperatures of 425 and 450 °C and pressures of 2 and 3 MPa for 180 min in argon atmosphere. The microstructural and mechanical properties of bonding have been characterized with different welding parameters such as bonding temperature and pressure. The microstructure was characterized by light optical microscope, scanning electron microscope and energy dispersive spectroscopy, while the mechanical properties were determined by tensile-shear tests and microhardness tests. The results obtained are discussed from both the microstructural and mechanical points of view. It was observed in the microstructural investigations that the interfacial oxide layer decreased with increasing of the bonding temperature and pressure. The maximum shear strength was found to be 131 MPa for the Al 7075 sample bonded at 450 °C and 3 MPa for 180 min. It is shown that in certain extent, the bonding temperature and bonding pressure have great effect on the joint shear strength. With the increasing of bonding temperature and pressure, the shear strength of the joints increases due to diffusion of atoms in the interface. The strength achieved after bonding were dependent on interface grain boundary migration and on grain growth during the bonding process. The maximum hardness value of the Al 7075 sample bonded at 450 °C, 3 MPa for 180 min is 92.5 HV_0.2. Increasing hardness with increasing temperature can be attributed to the formation of metallic bond at high temperatures and pressures.     

A new approach to determine the base shear of steel frame structures

Base shear (V) is the maximum lateral force that will occur due to seismic ground motion at the base of a structure. Calculations of base shear depend on a lot of factors such as soil conditions, level of ductility, fundamental period of vibration of the structure, etc. A great number of methodologies have been developed to determine the dynamic responses of individual frameworks. However, there is no well established empirical solution of the dynamic response of the problem due to the base shear of the steel frames. In this study, a formulation based on NN to determine the dynamic response of both braced and unbraced plane steel frames are provided. The presented formulation is a function of number of stories (ns), bays of the frames (nb), and soil types (Z). The training and testing patterns of the proposed NN formulation are obtained from linear Finite Element Analysis (FEA) solution. The NN-based formulation results are compared with the results obtained from numerical and some current design codes. The NN- based formulation results are found to be more accurate.     

Investigations the effects of fastener, glue, and composite material types on the strength of corner joints in case-type furniture construction

This study was carried out to determine the performance of different construction techniques on the diagonal compression and tension strength of case-type furniture corner joints, and to determine the effects on these joints of some factors including the type of joint, the type of composite board and the glue type. For this purpose, melamine-coated particleboard (MCP) and melamine-coated fiberboard (MCF) panels were bonded with polyvinyl acetate D3 (PVA D3), polyvinyl acetate D4 (PVA D4) and Desmodur VTKA (DVTKA) adhesives on spline joint (Sj), butt joints (Buj), biscuit joints (Bij), plain dowel joints (PDj), grooved dowel joints (GDj). It became evident that the diagonal tension and compression strength of the joints is influenced by panel material, type of adhesive and joints. The diagonal tension strength was greater than the diagonal compression strength of all L-type corner joints. The highest diagonal tension strength was obtained in MCF with DVTKA adhesive and GDj while highest diagonal compression strength was obtained in MCP with PVA D4 and Sj. In both tests, MCF corner joints were stronger than MCP corner joints. Furthermore, diagonal tension and compression strength of the joints glued with PVA D4 adhesive was higher than the similar joints glued with PVA D3 and DVTKA adhesives.     

Preparation and Thermodynamic Properties of Camphene/Stearic Acid Composites as Phase-Change Materials in Buildings

In this study, a series of shape-stabilized phase-change materials (PCMs) of camphene/stearic acid (CS) were prepared and their thermal properties were measured by differential scanning calorimetry. The results indicated that the mixture consisting of 60 mass% camphene and 40 mass% stearic acid is the most favorable as a PCM, in terms of the phase-change temperature and latent heat. Thereafter, the CS was absorbed in fly ash, pyroclastic, barite, and marble powder, which acts as a supporting material, to prepare four kinds of composite-based PCMs. DSC, FT-IR, and scanning electron microscopy measurements were made to investigate the structures and properties of the PCMs. DSC results showed that the latent heats of melting and freezing of the composite PCMs were sharply decreased. Morphology and structural characterization revealed that, in form-stable PCMs, the dispersion of the supporting materials in the camphene/stearic acid matrix is homogeneous and there is no chemical interaction between the CS and composites. The composite PCMs showed excellent thermal stabilities and reliabilities, when their phase-change temperatures were concerned. These indicate that the prepared composite-based PCMs are suitable for thermal energy storage because of their applicable temperature range, thermal reliability, and chemical stability.     

A multi-objective genetic algorithm for the hot mix asphalt problem

Neural Computing and Applications - It is desirable for the work done in any construction process to be both cost-effective and durable. A thorough consideration of the matter reveals that the...     

Spontaneous combustion liability of coal and coal-shale: a review of prediction methods

International Journal of Coal Science & Technology - This study presents a review of the various methods to predict the spontaneous combustion liability of coal and coal-shale. The relative...     

Section modulus of corner joints in furniture frames as engineering design criteria for their efficient construction

Since joints are often the weakest points in furniture construction a detailed analysis of the factors influencing their load bearing capacity and its effectiveness in utilizing the full strength of the wood is reported here.     

Fattening performance, carcass traits and meat quality characteristics of calves sired by Charolais, Simmental and Eastern Anatolian Red sires mated to Eastern Anatolian Red dams

Comparisons were made among calves sired by Charolais (C), Simmental (S) and Eastern Anatolian Red (EAR) breeds of bulls for fattening, carcass and meat quality traits when mated to EAR dams. C- and S-sired calves had 43.1% and 36.4% higher daily weight gain, 44.5% and 43.9% heavier final weight in fattening, respectively. Calves produced by C sires had best feed efficiency value (6.51 vs. 7.44 and 7.22) compared to the S and EAR sire breed groups. Carcasses of C- and S-sired calves had heavier weight, higher dressing percentage and greater Longissimus dorsi (LD) muscle area than those of EAR-sired calves. USDA yield grades were lower (P<0.01) for carcasses from C and S sires, and highest for carcasses from EAR calves. C-sired calves received higher (P<0.01) ratings for panel tenderness score, lower shear force value and number of chews before swallow than S- and EAR-sired progeny. Overall results of the study suggested that fattening performance, carcass and meat quality characteristics might be considerably improved by using C sires in the crossbreeding program as sire breed.