Transient Intensity Factors for a Parallel Crack in a Plate of a Functionally Graded Piezoelectric Material Under Thermal Shock Loading Conditions

A crack in a plate of a functionally graded piezoelectric material is studied under thermal shock loading conditions. The crack faces are supposed to be completely insulated. All material properties are assumed to be exponentially dependent on the distance from the crack line parallel to the boundaries of the plate. By using both the Laplace transform and Fourier transform, the thermal and electromechanical problems are reduced to a singular integral equation and a system of singular integral equations that are solved numerically. The stress and electric displacement intensity factors vs. time for various material constants and geometric parameters are calculated.     

Thermoelectromechanical Response of a Center Crack in a Symmetrical Functionally Graded Piezoelectric Strip

The thermoelectromechanical fracture problem for a symmetrical functionally graded piezoelectric strip containing a center crack parallel to the free boundaries is considered in this study. It is assumed that the thermoelectroelastic properties of the medium vary continuously in the thickness direction, and that the strip is under thermomechanical loadings. The crack faces are supposed to be insulated thermally and electrically. By using the Fourier transform, the thermal and electromechanical problems are reduced to singular integral equations, respectively, which are solved numerically. Numerical calculations are carried out, and detailed results are presented to illustrate the influence of the crack length and the material nonhomogeneity on the temperature-stress distributions and the stress intensity factor.     

Thermoelectromechanical Interaction Among Multiparallel Cracks in a Piezoelectric Material

This paper investigates the thermoelectromechanical interaction among multi parallel cracks in a piezoelectric material under a uniform heat flow and a uniform mechanical load far away from the crack region. The crack faces are supposed to be insulated thermally and electrically. By using the Fourier transform, the thermal and electromechanical problems are reduced to systems of singular integral equations, respectively. The singular integral equations are solved numerically. Numerical calculations are carried out, and detailed results are presented to illustrate the influence of the thermoelectromechanical interaction on the stress and electric displacement intensity factors.     

Effects of Crack Surface Conductance on Intensity Factors for a Functionally Graded Piezoelectric Material Under Thermal Load

Effects of crack surface conductance on intensity factors for a functionally graded piezoelectric material under thermal load are investigated. The heat flux through the crack is assumed to be proportional to the local temperature difference. Moreover, two models for more realistic crack face electric boundary conditions are proposed. By using the Fourier transform, the thermal and electromechanical problems are reduced to a singular integral equation and a system of singular integral equations, respectively, which are solved numerically. Detailed results are presented to illustrate the influence of the thermal and electric conductance on the stress and electric displacement intensity factors.     

Transient Response of a Cracked Piezoelectric Strip Under Thermoelectric Loading

In this study, the theoretical analysis of a transient piezothermoelastic problem is developed for a piezoelectric strip with a parallel crack under static electric loading and thermal shock loading conditions. The crack faces are supposed to be insulated thermally and electrically. By using both the Laplace transform and the Fourier transform, the thermal and electromechanical problems are reduced to a system of singular integral equations, respectively, which are solved numerically. Some numerical results for the temperature change, the stress and electric displacement distributions, and the energy density factor as well as the stress and electric displacement intensity factors in a transient state are shown in figures.     

EXACT THERMOELECTROELASTICITY SOLUTION FOR A PENNY-SHAPED CRACK IN PIEZOELECTRIC MATERIALS

This paper investigates the electromechanical fracture behavior of a penny-shaped crack in piezoelectric materials subjected to a uniform heat flow far away from the crack region. The crack is treated as isothermal. First, the temperature field is obtained by using the Hankel transform technique. The thermoelectromechanical field is then investigated by solving the themopiezoelectoelasticity governing equations. The explicit solutions for the stress intensity factors near the crack tip are presented. The exact solution for the whole-field stresses and electric displacements are obtained.     

The limited electrically permeable crack model in linear piezoelasticity

The problem of a crack in a piezoelectric material under electromechanical loading is considered. The exact solution, obtained in this work, includes the unknown a priori normal component of the electric displacement inside the crack. Several different physical assumptions associated with limited electric permeability of the crack are utilized to determine those unknown electric fluxes through the crack boundaries. Analytical formulae for the stress and electric intensity factors are derived. The effects of electric boundary conditions (limited permeability) at the crack surface on the basic parameters of fracture mechanics are analyzed and some features of the solution are discussed. If the permeability of the medium inside the crack tends to zero or is very large the extreme results i.e. impermeable or permeable crack solution are obtained.     

Electromechanical diagnostic method for monitoring cracks in polymer electrolyte fuel cell electrodes

A significantly challenging issue in polymer electrolyte fuel cells (PEFCs) is the insufficient durability of the membrane electrode assembly (MEA) electrodes caused by crack formation and growth. A decrease in interconnections of the electrical pathways in the electrodes leads to poor performance and durability of the PEFCs. Therefore, fundamental understanding of the nature of the crack formation and growth in electrodes is critical for improving fuel cell durability. In this study, an electromechanical diagnostic method is proposed to monitor the cracks in the PEFC electrodes. The electrical resistance of electrode is measured through the in situ four-wire electrical resistance measurements under tension. The crack areal density is proposed and measured as a quantitative parameter to define the presence of cracks in the electrodes using an optical microscope. It is found that the change of electrical resistances under tension increases with the electrode thickness (i.e., Pt loading), which results from the crack growth in the electrodes. This electromechanical diagnostic method is useful for understanding the crack mechanics consisting of initiation, propagation, and widening stages, and expected to facilitate the design of robust electrodes for highly durable fuel cells.     

Transient Thermoelectroelastic Response of a Functionally Graded Piezoelectric Strip with Two Parallel Axisymmetric Cracks

In this article, the problem of two parallel axisymmetric cracks in a plate of a functionally graded piezoelectric material (FGPM) strip is analyzed under transient thermal loading conditions. It is assumed that the thermoelectroelastic properties of the strip vary continuously along the thickness of the strip, and that the crack faces are supposed to be insulated thermally and electrically. By using both the Laplace and Hankel transforms, the thermal and electromechanical problems are reduced to two systems of singular integral equations. The singular integral equations are solved numerically, and a numerical method is then employed to obtain the time dependent solutions by way of a Laplace inversion technique. Systematic numerical calculations are carried out, and the field intensity factors versus time are presented for various values of dimensionless parameters representing the crack geometry and the material non-homogeneity.     

The Crack Problem in Piezoelectric Strip Under Thermoelectric Loading

This paper investigates the thermoelectromechanical fracture behavior of a parallel crack in a piezoelectric strip under thermoelectric loading. The crack faces are supposed to be insulated thermally and electrically. By using the Fourier transform, the thermal and electromechanical problems are reduced to a system of singular integral equations, respectively, which are solved numerically. Numerical calculations are carried out, and the energy density factor as well as the stress and electric displacement intensity factors are presented for various values of dimensionless parameters representing the size and the location of the crack and the magnitude of the electric loading.     

Transient Thermoelectromechanical Response of a Piezoelectric Strip with Two Parallel Cracks of Different Lengths

This work is concerned with the thermoelectromechanical fracture behavior of two parallel cracks of different lengths in a piezoelectric material strip under thermal shock loading. The crack faces are supposed to be insulated thermally and electrically. By using both the Laplace transform and the Fourier transform, the thermal and electromechanical problems are reduced to two systems of singular integral equations, respectively, which are solved numerically. A numerical method is employed to obtain the time dependent solutions by way of a Laplace inversion technique. The intensity factors versus time for various geometric parameters are calculated and presented in graphical forms. Temperature change, the stress and electric displacement distributions in a transient state are also included.     

Transient thermoelectroelastic response of a piezoelectric material strip with two parallel cracks in arbitrary positions

This work is concerned with the thermoelectromechanical fracture behavior of two parallel cracks in arbitrary positions of a piezoelectric material strip under thermal shock loading. The crack faces are supposed to be insulated thermally and electrically. By using both the Laplace transform and the Fourier transform, the thermal and electromechanical problems are reduced to two systems of singular integral equations. The singular integral equations are solved numerically, and a numerical method is then employed to obtain the time-dependent solutions by way of a Laplace inversion technique. The intensity factors versus time for various geometric parameters are calculated and presented in graphical forms. The temperature, stress and electric displacement distributions in a transient state are also included.     

Industrial energy use-III. The prospects for providing motive power in a machine tool shop from a centralized hydraulic system

This paper describes a comparative economic study of electric and hydraulic power transmission. the data and results apply to a particular site, but the methodology is generally applicable. the study used mathematical models of the various components in electromechanical and hydraulic power transmission systems to determine in each case the necessary energy input to supply a specified load cycle at the machine tool spindle. the study concludes that a central hydraulic system on the site studied would operate with 20 per cent less energy consumption than the existing electromechanical system. the economic appraisal of the merits of electromechanical and hydraulic power distribution systems is dominated by capital savings in the final drives; these are assessed.     

Performance analysis of a directly coupled photovoltaic water-pumping system

The application of a stand-alone directly coupled photovoltaic (PV) electromechanical system for water pumping has increased in remote areas of developing countries. In this work, the performance of a PV-powered dc permanent-magnet (PM) motor coupled with a centrifugal pump has been analyzed at different solar intensities and corresponding cell temperature. The results obtained by experiments are compared with the calculated values, and it is observed that this system has a good match between the PV array and the electromechanical system characteristics. Through manual tracking (i.e., changing the orientation of PV array, three times a day to face the sun) the output obtained is 20% more compared to the fixed tilted PV array. It has been observed that the torque-speed curve at low solar intensities for a PV electromechanical system should be steeper than at higher solar intensities, and the load torque-speed curve should be as steep as possible in the operating region with low starting torque. The performance analysis will be helpful to select the suitable PV electromechanical system for water-pumping applications.     

Examination of a crack found in a welded joint of steel TTStE36 after 13 years service

This article reports the study of a crack found in an in-service shell. After analyzing the chemical compositions, microstructure of the welded joint of steel TTStE36, and according to the macro-crack, the microstructure of the crack fracture, the character of the crack is determined. It is a cold crack. The genesis of this cold crack is analyzed, and measures to avoid such a cold crack in welded joint of steel TTStE36 are put forward.     

Stability of a crack in a cantilever beam undergoing large plastic deformation after impact

A simple model is employed to determine the dynamic response of a rigid-perfectly plastic cantilever beam with an attached tip mass and a crack, taking into account the weakening effect of the crack. The crack is assumed to be located at the base of the beam, and an initial velocity is imparted to the tip mass. The subsequent stability of the crack is considered by calculating the tearing modulus based on the J-integral associated with the deflecting beam. For the example of circumferential cracks in thin-walled piping, whose idealized geometry models some stress corrosion cracks found in service, radial propagation and instability are found to be more likely than circumferential. Once a crack penetrates the wall, however, stability in the circumferential direction is found to depend in a complex way upon loading and crack geometry.     

业主技术管理在水电站机电投资目标控制中的应用与启示

为提高水电站机电设备的投资效益,以ZJKF项目为例,结合建设项目管理实践,从业主技术管理的角度分析了项目特点及实施阶段机电设备投资目标决策过程,阐述了技术管理在机电设备投资目标控制中的具体应用及其效果,并总结了技术管理在机电设备投资目标控制中的应用启示,为建设项目机电设备投资目标控制工作提供了有益参考。     

浅析加强煤矿机电管理和促进机电设备升级

煤矿机电故障极易导致矿难事故,提高机电管理水平和促进机电设备升级有助于降低矿井事故的发生。通过了解国内煤矿机电管理的不足,提出一些改进的措施,并指出煤矿机电一体化的优势,智能化是其未来的发展方向。     

Transient thermal fracture analysis of a penny-shaped magnetic and dielectric crack in a magnetoelectroelastic cylinder

The problem of penny-shaped magnetic and dielectric crack in a magnetoelectroelastic cylinder is investigated under thermal shock load. The problem is reduced to solve three coupled Fredholm integral equations. The field intensity factors are derived. Numerical results of crack opening displacement intensity factors are presented, and the effects of thermal shock time, crack configuration, and magnetoelectrical crack surface conditions on crack propagation and growth are evaluated. Among others, the larger cylinder's radius, the easier to propagate the crack is. For a fixed crack configuration, magnetoelectrical crack surface conditions have different effects on crack propagation as well.     

Inhibition of a curvilinear bridged crack by induced thermoelastic stress field

Temperature changes near the end of a curvilinear crack in the presence of end areas with cohesive forces of the material are considered. It is assumed that these areas adjoin to the crack tip and their sizes are comparable with the crack size. The goal of local changes of temperature is to delay or inhibit the growth of a curvilinear crack. A boundary value problem on equilibrium of a bridged curvilinear crack under the action of external tensile loads, induced thermoelastic temperature field, and tractions in the bonds preventing its disclosure is reduced to the system of nonlinear singular differential equations with a Cauchy-type kernel. Normal and tangential tractions in the bonds are found from the solution of this system. The stress intensity factors are calculated. The condition of limit equilibrium of a curvilinear crack with an end area is formed based on two-parameter fracture criterion.