Fatigue fracture failure analysis of guide valve based on welding defects

This research paper presents a failure analysis conducted on the guide valve located at the bottom of the primary outlet buffer tank in the reciprocating machine of the diesel hydrogenation unit during its operation. Various methods, including in situ observation, macroscopic fracture analysis, metallographic analysis, microscopic fracture observation, material composition analysis, and hardness testing, were employed to investigate the cause of the failure. The findings indicate that the failure resulted from insufficient fusion between the valve body and the flange of the guide shower valve during the manufacturing and welding process. This lack of fusion led to fatigue failure of the weld during operation, ultimately resulting in valve cracking and detachment. The presence of fatigue failure is widespread and poses a significant threat in petrochemical plants and their surrounding environments, given the equipment’s exposure to alternating working conditions and vibrations. This failure analysis serves as a valuable reference for future quality inspections of petrochemical equipment parts. Additionally, it assists enterprises in mitigating risks throughout the design, installation, and maintenance processes, thereby reducing the likelihood of similar accidents occurring

Fracture mechanics for multilayers with penny-shaped cracks subjected to dynamic torsional loading

This paper provides a method for investigating the penny-shaped interface crack configuration in orthotropic multilayers under dynamic torsional loading. The multilayer is said to have finite height along the direction normal to the interfaces. By utilizing Laplace transform and Hankel transform technique, the general solution for each layer is derived. The Dual integral equations of the entire elastic region are then obtained through introducing the mechanical boundary and layer interface conditions. The stress intensity factors (SIFs) are computed by solving Dual integral equations numerically in Laplace transform domain. The solution in time domain is obtained by utilizing numerical Laplace inverse. Numerical example shows that the main advantage of the present model is its ability for treating multiple crack configurations in multilayers and the number of layers can be sufficiently large. The present model can also treat crack problems for functionally graded materials (FGMs) with arbitrarily distributed and continuously varied material properties by subdividing the FGM into a number of thinner layers such that the elastic properties are constants within each individual layer, but they vary from layer to layer

Analysis of fiber breaking in fiber/matrix composites under torsional loads

The initiation of multiple cracks in a fiber/matrix composite subjected to a torsional load is studied. The composite is made of a cylindrical fiber surrounded by a matrix of different properties. A periodic array of cracks is assumed to exist in the fiber along its central axis. A dual integral equation is formulated in terms of equivalent crack face loads. The effects of crack spacing on the crack tip field intensity factor, the stress, the torque, and the equivalent stiffness of the fiber are investigated and displayed graphically

Transient thermal fracture of piezoelectric materials structures

It is generally well understood that thermal shock conditions, which arise during sudden heating or cooling of a solid, can result in very high stresses. If the thermal transient is severe enough, sudden fracture may occur. The degree of damage and strength degradation of ceramics subjected to fluctuating thermal environments is a major limiting factor in relation to service requirements and lifetime performance. Early studies to quantify the severity of thermal shock in a plate of finite thickness attempted to draw a correlation between the magnitude of maximum tensile stress on the plate surface and the likelihood of failure. This approach assumes that there are no pre-existing surface flaws. A more sophisticated fracture analysis incorporates an edge crack in the transient stress analysis and thus the degree of severity of any given thermal shock is characterized in terms of the stress intensity factor which is a function of crack size and relevant heat transfer and thermo-elastic coefficients [1-3]

Transient fracture of a layered magnetoelectroelastic medium

Most magnetoelectroelastic composites were developed in the form of a composite laminate by alternating the ferromagnetic layers and ferroelectric layers during stacking. Presence of interfacial crack may influence the magneto-electro-mechanical coupling behavior of magnetoelectroelastic materials considerably. This paper describes a method to analyze the transient response of a layered magnetoelectroelastic medium of finite size with an interface crack. Based on Fourier and Laplace transforms, the boundary value problem is reduced to a system of generalized singularity integral equations in the Laplace transform domain. By utilized numerical Laplace inversion, the time-dependent full field solutions are obtained in the time domain. Effects of medium size, crack-face electric and magnetic boundary conditions on the dynamic crack tip fields are studied. By investigating an interface notch of finite gap thickness, the electric and magnetic properties of the medium inside the notch are included in the analytical model so that the applicability of crack-face electric and magnetic boundary conditions on the transient response of the magnetoelectroelastic medium can be investigated

Applicability of the crack face electrical boundary conditions in piezoelectric mechanics

The electrical boundary conditions on the crack faces and their applicability in piezoelectric materials are discussed. A slit crack and a notch of finite thickness in piezoelectric materials subjected to combined mechanical and electrical loads is considered. Here, a crack is defined as a notch without thickness, which is filled with air or vacuum. The crack or notch is perpendicular to the poling direction of the medium. The ideal crack face electrical boundary conditions, i.e., the electrically permeable crack and the electrically impermeable crack, are investigated first. Then dependence of the field intensity factors on notch thickness at the notch tips is analyzed to obtain a closed-form. The results are compared with the ideal crack solutions. Some useful results are found

Multiple crack problem in nonhomogeneous composite materials subjected to dynamic anti-plane shearing

A recently developed method for the dynamic response of nonhomogeneous composite material subjected to in plane loading is further extended to accommodate the case of anti-plane loading. It is assumed that the composite material is orthotropic and all the material properties vary arbitrarily along the thickness direction. In the analysis, the elastic region is modeled using a series of layers of infinite length, with each layer having slightly different properties. By utilizing the Laplace transform and Fourier transform technique, the general solution for each layer is derived. The singular integral equations of the entire elastic region are then obtained through introducing the mechanical boundary and layer interface conditions via the flexibility/stiffness matrix approach. The integral equations are solved by weighted residual value method. As the numerical illustrations, the dynamic stress intensity factors for a cracked metal-ceramic joint with a functionally graded interlayer under sudden applied stress on the joint surface are presented. The results demonstrate that there existing optimal nonhomogeneity parameter at which the stress intensity factor is minimized

Thermoelastic fracture mechanics for nonhomogeneous material subjected to unsteady thermal load

This article provides a comprehensive treatment of cracks in nonhomogeneous structural materials such as functionally graded materials. It is assumed that the material properties depend only on the coordinate perpendicular to the crack surfaces and vary continuously along the crack faces. By using a laminated composite plate model to simulate the material nonhomogeneity, we present an algorithm for solving the system based on the Laplace transform and Fourier transform techniques. Unlike earlier studies that considered certain assumed property distributions and a single crack problem, the current investigation studies multiple crack problems in the functionally graded materials with arbitrarily varying material properties. The algorithm can be applied to steady state or transient thermoelastic fracture problem with the inertial terms taken into account. As a numerical illustration, transient thermal stress intensity factors for a metal-ceramic joint specimen with a functionally graded interlayer subjected to sudden heating on its boundary are presented. The results obtained demonstrate that the present model is an efficient tool in the fracture analysis of nonhomogeneous material with properties varying in the thickness direction

Anti-plane mechanical and in-plane electrical fields for a finite electrode/punch on a finite piezoelectric layer

The problems of a surface electrode and a rigid punch on a finite piezoelectric layer are considered in this paper. The resultant force and the accumulated electric charge on the electrode/punch are prescribed. Closed-form solutions for the electromechanical fields at the electrode/punch tip are obtained and are expressed in terms of the applied strain and electric field intensity factors. For infinite layer thickness, the strain and electric field intensity factors are obtained in closed-form. For finite layer thickness, the strain and electric field intensity factors are obtained numerically by the singular integral equation technique. The effect of layer thickness on the electrode/punch tip fields is discussed. It is found that the field intensities at the electrode/punch tip can be reduced considerably by decreasing layer thickness. In addition to the single electrode/punch problem, this paper also provides a solution technique for two collinear surface electrodes/punches on a finite piezoelectric layer. The effect of the relative distance between the two electrodes/punches on the electromechanical fields in the piezoelectric layer is also discussed