Experimental Study of Hysteresis in Clayey Soils under Compression

The energy dissipation for one cycle of clay soil deformation over the area of ​​a hysteresis loop under conditions of one-dimensional deformation has been experimentally studied. Several series of trials were carried out under different conditions of soil density and moisture and different loading modes. It was established by the experiments that after several cycles of loading and unloading of the samples, the transient process of the closed loop formation ends and certain dependences of stress on deformations are established in the sections of the ascending and descending branches of the hysteresis loop. To determine these dependencies, rheological relations obtained directly from the hysteresis loop by approximating the arcs of its contour have been used. By integrating the approximating rheological dependences along the branches of the loop, the dissipated energy per deformation cycle has been obtained as a function of cyclic deformation amplitude, measured by the area of the hysteresis loop. Experiments on obtaining a hysteresis loop were carried out on a compression device with a cyclic sample. Samples with different states of density and moisture content were produced by consolidating a paste having yield point moisture under different pressures. Several series of experiments have been carried out. In the first series, soil absorption coefficients were derived for different states of density-moisture at different loading rates. In the second series, three types of clayish soil (clay, loam, sandy loam) were studied. Dissipation coefficients have been found out for the indicated soils. In the third series, three types of clay soil were tested under different conditions of density and moisture. The dissipation coefficients have been obtained. In the fourth series, the dependences of the absorption coefficient on the amplitude value of the cyclic stress for three types of clay soil were disclosed. It was found that a change in the loading rate within the range from 0.05 MPa to 0.2 MPa does not lead to the significant change in the absorption coefficient, the increase in the number of clay fractions in the sample leads to an increase in the absorption coefficient, a change in the amplitude of cyclic loading (in the indicated range of change) does not affect the absorption coefficient.

A Novel Notion of Local and Nonlocal Deformation-Gamuts to Model Elastoplastic Deformation

Localization and nonlocalization are characterized as a measure of degrees of separation between two material points in material’s discrete framework and as a measure of unshared and shared information, respectively, manifested as physical quantities between them, in the material’s continuous domain. A novel equation of motion to model the deformation dynamics of material is proposed. The shared information between two localizations is quantified as nonlocalization via a novel multiscale notion of Local and Nonlocal Deformation-Gamuts or DG Localization and Nonlocalization. Its applicability in continuum mechanics to model elastoplastic deformation is demonstrated. It is shown that the stress–strain curves obtained using local and nonlocal deformation-gamuts are found to be in good agreement with the Ramberg–Osgood equation for the material considered. It is also demonstrated that the cyclic strain hardening exponent and cyclic stress–strain coefficient computed using local and nonlocal deformation-gamuts are comparable with the experimental results as well as the theoretical estimations published in the open literature.

Effect of high-frequency PCB laminate on thermal cycling behavior of electronic packaging structures

PurposeAs the solution to improve fatigue life and mechanical reliability of packaging structure, the material selection in PCB stack-up and partitioning design on PCB to eliminate the electromagnetic interference by keeping all circuit functions separate are suggested to be optimized from the mechanical stress point of view.Design/methodology/approachThe present paper investigated the effect of RO4350B and RT5880 printed circuit board (PCB) laminates on fatigue life of the QFN (quad flat no-lead) packaging structure for high-frequency applications. During accelerated thermal cycling between −50 °C and 100 °C, the mismatched coefficients of thermal expansion (CTE) between packaging and PCB materials, initial PCB warping deformation and locally concentrated stress states significantly affected the fatigue life of the packaging structure. The intermetallics layer and mechanical strength of solder joints were examined to ensure the satisfactorily soldering quality prior to the thermal cycling process. The failure mechanism was investigated by the metallographic observations using a scanning electron microscope.FindingsTypical fatigue behavior was revealed by grain coarsening due to cyclic stress, while at critical locations of packaging structures, the crack propagations were confirmed to be accompanied with coarsened grains by dye penetration tests. It is confirmed that the cyclic stress induced fatigue deformation is dominant in the deformation history of both PCB laminates. Due to the greater CTE differences in the RT5880 PCB laminate with those of the packaging materials, the thermally induced strains among different layered materials were more mismatched and led to the initiation and propagation of fatigue cracks in solder joints subjected to more severe stress states.Originality/valueIn addition to the electrical insulation and thermal dissipation, electronic packaging structures play a key role in mechanical connections between IC chips and PCB.

A Liquefaction Study Using ENN, CA, and Biogeography Optimized-Based ANFIS Technique

In any construction projects,assessment of liquefaction potential induced due to seismic excitation during earthquake is a critical concern.The objective of present model development is to classify and assess liquefaction potential of soil.This paper addresses Emotional Neural Network(ENN), Cultural Algorithm(CA) and biogeography optimized(BBO) based adaptive neuro-fuzzy inference system (ANFIS) for liquefaction study.The performance of neural emotional network and cultural algorithm has been also discussed. BBO-ANFIS combines the biogeography features to optimize the ANFIS parameters to achieve higher prediction accuracy.The model is trained with case history of liquefaction databases.Two parameters are used as input such as the cyclic stress ratio and standard penetration test (SPT) value.The performance of these models was assessed using different indexes i.e. sensitivity, specificity, FNR, FPR and accuracy rate.The performance of all models is compared.Among the models, the BBO-ANFIS model has been outperformed and can be adopted as new reliable technique for liquefaction study.

DEVELOPMENT OF DIES WITH DIFFERENTIATED CLAMP FOR CUTTING BLANKS FOR PRECISION STAMPING

A large contribution to the final cost of machine-building products is made by the efficiency of blank production, in which a waste-free shear cut is used. The most promising for the implementation of the method of shear cutting are dies with a differentiated clamping of rolled products. The aim of the work is to develop a new die design with a differentiated clamping of rolled products with high technical and economic characteristics and recommendations for the design of such equipment. On the basis of the developed graph of constructions of dies with a differentiated clamping of rolled products, design features have been identified, which made it possible to create a new die design. Compared with the known structures, in the stamp of the DSEA structure, the transverse dimensions and weight are reduced by an average of 25%, and the height of the open stamped space – by 10%. In the process of dividing in the vertical plane, a constant position of the rolling axis is ensured. The transfer of force to the clamp through the rolling is excluded. The stamp has high rigidity. The stamps of the DSEA design have been introduced at the Odessa PJSC "Stroygidravlika". The economic effect of the implementation was 100000 UAH. Acceptance test results showed that the dies of the new design are efficient and reliable in operation. The quality of the cut workpieces corresponds to the quality indicators of the workpieces cut on modern similar equipment. On the basis of theoretical analysis, experimental studies and operating experience of dies with differential clamping of rolled products, known and formulated new recommendations for the design of such dies. The main ones are: it is necessary to provide a differentiated clamping of rolled products on both sides of the separation plane, subject to the condition that the clamping force should be one and a half times greater than the cutting force; the die body is preferably box-shaped to compensate for thrust forces and torsional moments of forces; the power parts of the stamp must be made in a closed form with stiffening ribs to ensure strength under cyclic stress conditions.

Evaluation of the durability of mastic deck covering based on polymer composites in the range of operating stresses and temperatures

The urgency of anticorrosive protection issues of ship hulls, deck structures, mechanisms, etc., as one of the main problems of the naval, is noted. One of the options for its effective solution is the use of coatings based on various polymer-composite materials. The authors substantiate the need for a preliminary assessment of the reliability and durability of such coatings, taking into account high humidity and aggressiveness of the operating environment, the corrosion of the repaired surfaces, the cyclic effect of stresses and alternating temperatures, etc. Proceeding from this, using the example of multicomponent polymer-composite compositions of the “Sprut” type, methodological approaches to the study of the polymer-composites durability for ship repair are considered. Their comparative characteristics are given. A mathematical model for assessing the durability of polymer-composite materials and coatings based on them is described, and the experimental studies’ results of their durability under static and cyclic stress in the operating temperature range are presented. The obtained results of theoretical and experimental studies are important for development of the methodological approaches to increasing the durability of mastic deck coatings based on polymer composite materials and the development of practical guidelines for the use of adhesives in shipbuilding and ship repair. The research results make it possible to develop new and improve the adopted technologies for the use of protective coatings on the structures of ship hulls and deck structures. Thus, the problems of the water transport operation, associated with the anti-corrosion protection of ship hull and deck structures and their repair, can be solved.

Degradation mechanisms analysis for SiC power MOSFETs under repetitive power cycling stress

In this work, investigation on the degradation behavior of the 1.2-kV/52-A silicon carbide (SiC) power MOSFETs subjected to repetitive slow power cycling stress have been performed. Electric characteristics have been characterized periodically over the stress and the respective degradation mechanisms also have been analysed. A comprehensive degradation analysis is further conducted after the aging test by virtue of the X-ray inspection system, Scanning Acoustic Microscope (SAM), Scanning Electron Microscope (SEM) and emission microscope (EMMI), etc. Experimental results reveal that both the degradation of gate oxide on chip-level and the degradation of the bond wire and solder layer on package-level have emerged over the cyclic stress. Specifically, growths of threshold voltage (Vth) and gate leakage current (Igss) are thought to be relevant with the degradation of gate oxide by SiC/SiO2 interface states trapping/de-trapping electron on chip-level, while the appearances of the fatigue of bond wire and the delamination of solder layer imply the degradation on package-level. This work may provide some practical guidelines for the assessments towards the reliability of SiC power MOSFETs in power conversion system.