Analysis of a radial crack in cross-ply laminates under uniaxial tension

The problem of a radial crack in cross-ply laminates under uniaxial tension is investigated in this paper. The normalized stress intensity factors are obtained by the modified mapping collocation method which is based on analytic complex function theory of complex variables. The present results for an isotropic infinite plate show good agreement with existing solutions. In the range of small crack length, the stress intensity factor for a radial crack in cross-ply laminates under uniaxial tension becomes larger as the percentage of 0° plies increases. However in the range of large crack length, it is insensitive to the percentage of 0° plies.     

Application of residuals from regression of experimental mode shapes to locate multiple crack damage in a simply supported reinforced concrete beam

The objective of the study was to propose an effective, simple and reliable technique to determine the location of triple-crack damage in a simply-supported reinforced concrete beam using the method of mode shape regression. The study required simply supported finite element reinforced concrete beam models to be constructed with one as control and another as the test beam with predetermined triple-cracks along the length of the beam. The technique necessitated the performance of linear and Eigen analyses on the control beam, and nonlinear analysis on the beam with triple-cracks. Residuals obtained from regression of the mode shape using the Chebyshev series rational on the modal frequencies and transformation and application into the fourth order centered finite divided difference formula were used. The use of the regressed mode shapes for the reinforced concrete beam model showed large residuals around the areas of the crack damage. The results showed that the method was successful in determining the locations of the triple cracks and was comparable with other techniques proposed by other researchers in terms of its simplicity and reliability.     

Analysis of a kinked crack in an anisotropic material under antiplane deformation

This paper analyzes the asymptotic problem of a kinked crack in an anisotropic material under antiplane deformation. Using the linear transformation method proposed in this paper, a solution to the asymptotic problem of a kinked crack in an anisotropic material can be obtained from the solution of the corresponding isotropic kinked crack problem. The exact solution of the stress intensity factor for the kinked crack in the anisotropic material is obtained from the solution of the isotropic problem. The effect of the kink angle and two anisotropic parameters on the stress intensity factor is discussed for the inclined orthotropic material as well as the anisotropic material. In order to verify the exact solution of the stress intensity factor, numerical calculations are performed by using finite element analysis.     

Stress concentration factor due to a circular hole in functionally graded panels under uniaxial tension

The effect of the material property inhomogeneity on the stress concentration factor (SCF) due to a circular hole in functionally graded panels is numerically investigated. The multiple isoparametric finite element formulation is used to simulate the elastostatic boundary value problem. A parametric study is performed by varying the functional form and the direction of the material property gradation. The material property inhomogeneity is characterized by the intrinsic inhomogeneity length scale, modulus ratio and the power-law index. The results from our parametric study showed that the SCF is reduced when Young's modulus progressively increased away from the hole. The angular position of the maximum tensile stress on the surface of the hole remains unaffected by the material property inhomogeneity. The SCF is seen to be most influenced by the power-law index, followed by the variation of the inhomogeneity length scale. The SCF is least affected by the modulus ratio.     

Analysis of a conducting crack in an electrostrictive ceramic under combined electric and mechanical loading

A conducting crack in an electrostrictive ceramic under combined electric and mechanical loading is investigated. Analysis based on linear dielectric model predicts that the surfaces of the crack are not open completely but they are contact near the crack tip. The complete solution for the crack with a contact zone in a linear electrostrictive ceramic under combined electric and mechanical loading is obtained by using the complex variable formula. The asymptotic problems for a semi-infinite crack with a partial opening zone as well as for a fully open semi-infinite crack in a nonlinear electrostrictive ceramic are analyzed in order to investigate the effect of the electrical nonlinearity on the stress intensity factor under small scale nonlinear conditions. Particular attention is devoted to a finite crack in the nonlinear electrostrictive ceramic subjected to combined electric and mechanical loading. The stress intensity factor for the finite crack under small scale nonlinear conditions is obtained from the asymptotic analysis.     

弯管内拱壁含环向贯穿裂纹的极限载荷分析研究

含环向贯穿裂纹的弯管在受平面弯矩时明显地降低了其极限载荷,因此对含裂纹弯管的极限载荷研究是很有必要的。研究工作涉及了基于不同的裂纹角度、壁厚以及平均弯曲半径的弯管,进而比较了这些因素对弯管极限载荷的影响。利用ABAQUS软件对弯管进行三维有限元分析,得到了弯矩与末端转动曲线,以及用TES（Twice—elastic slope）方法得到每种情况的极限载荷值,该值与现有的部分工程方法进行了对比分析。结果表明,在大多数情况下工程法相对于有限元法保守。     

Application of the ultrasonic propagation imaging system to an immersed metallic structure with a crack under a randomly oscillating water surface

Ultrasound is widely used and studied to satisfy the increased demands of the Non-destructive evaluation (NDE) and testing of underwater structures. However, because of the large size and mass of underwater structures, such as submarines, ship hulls, or nuclear reactor pipe lines, it is difficult to inspect the structures during operation. This underwater NDE technology is challenging but could be highly beneficial because the time and cost of maintenance will be effectively reduced. We propose an NDE method for immersed structures using an ultrasonic propagation imaging system with a piezoelectric sensor. The underwater sensing capability of a piezoelectric sensor is experimentally demonstrated using an aluminum plate specimen. A piezoelectric sensor can compensate for the decreased signal amplitudes due to leaky waves that are generated on interfaces between structures and water, since water transmits signals better than air. Additionally, a piezoelectric sensor can be applied even if the water surface is oscillating. Using these properties, the laser induced guided Ultrasonic propagation imager (UPI) inspected a T-shaped steel structure with a 2-mm crack on the weld zone. The inspection was implemented in three cases: a specimen without water, a specimen immersed in water and a specimen immersed in water with a randomly oscillating surface. The crack was visualized and measured using the ultrasonic wave propagation imaging algorithm, the adjacent wave subtraction algorithm, and the variable time window amplitude mapping algorithm. In the case with a randomly oscillating water surface, the laser pulse was refracted randomly based on Snell’s law. This phenomenon may cause degradation of the inspecting results. However, a repeated scanning process and outlier elimination led to an improved signal-to-noise ratio such that it was able to detect the crack. These results demonstrate the possibility to apply the laser UPI to submerged structures even if the water surface is randomly oscillating.     

Stress intensity factors of a crack lying in a viscoelastic layer embedded in two different media under an anti-plane concentrated load

A general solution to the problem of a crack lying in a viscoelastic layer sandwiched between two different media under an anti-plane concentrated load is presented. The fundamental elastic solution is obtained as a rapidly convergent series in terms of complex potentials via successive iterations of Möbius’ transformation in order to satisfy continuity conditions on two different interfaces. Based on the correspondence principle, the Laplace-transformed viscoelastic solution is then directly determined from the corresponding elastic solution. Therefore, the time-dependent mode-III stress intensity factor (SIF) of the crack tip can be solved numerically in a straightforward manner. Furthermore, the viscoelastic moduli of polyurethane at various temperatures are regressed from a uni-axial test with a constant load while a standard solid model is applied to formulate the viscoelastic constitutive equation. Finally, the effects of working temperature, boundary conditions and the geometric relation on the SIF are also discussed.     

On the technique used to determine plasticity margin in high-speed deformation under high pressure

The work treats the determination of metal plasticity margin. Cylindrical Fe specimens were tensioned in a high-pressure machine. Constitutive equations and plasticity margin were determined from experiments, the specimen material being incompressible and isotropic. A new technique is proposed to determine plasticity margin by solving a boundary value problem modelling breaking tests. The stress–strain states until the moment of fracture were calculated with the application of the variable separation method based on the variational formulation of the boundary value problem. Plasticity margin calculated from the solution by the method is compared to the experimental one.     

Elastodynamic response of a crack perpendicular to the graded interfacial zone in bonded dissimilar materials under antiplane shear impact

A solution is given for the elastodynamic problem of a crack perpendicular to the graded interfacial zone in bonded materials under the action of antiplane shear impact. The interfacial zone is modeled as a nonhomogeneous interlayer with the power-law variations of its shear modulus and mass density between the two dissimilar, homogeneous half-planes. Laplace and Fourier integral transforms are employed to reduce the transient problem to the solution of a Cauchy-type singular integral equation in the Laplace transform domain. Via the numerical inversion of the Laplace transforms, the values of the dynamic stress intensity factors are obtained as a function of time. As a result, the influences of material and geometric parameters of the bonded media on the overshoot characteristics of the dynamic stress intensities are discussed. A comparison is also made with the corresponding elastostatic solutions, addressing the inertia effect on the dynamic load transfer to the crack tips for various combinations of the physical properties.     

A technique for localized heating in tissue: an adjunct to tumor therapy.

Increasing evidence of the beneficial effects of hyperthermia in the treatment of tumors, particularly when combined with radiation therapy or chemotherapy, has created the need for practical methods of localizing heat in arbitrary tissue volumes. Heating superficial transplanted animal tumors in hot-water baths has been of considerable importance in research, but the method has very limited clinical application. Microwave diathermy and ultrasound diathermy are capable of greater penetration than external conduction heating, but are also generally limited to the heating of superficial tissue volumes. A more direct method for localized tissue heating is proposed: localized electric current fields produced with carefully specified electrode configurations. This technique, although often quite invasive, offers the possibility of heat localization in almost any treatment volume specified by the therapist. Variations in electrical and thermal properties of tissues can be exploited to improve the architecture of the treatment plan. Several electrode configurations are illustrated. Limitations of the technique are discussed.     

Reaction layer formation on bronze with an S-P extreme pressure additive in boundary lubrication under increasing load: I

An extreme pressure film formed on a phosphor bronze sliding against hardened ball-bearing steel with an S-P compound in mineral oil was examined. Film formation under boundary lubrication with continuously increasing load was observed using surface analytical methods. The concentration of tin in the reaction layer was found to be more enhanced than that of other elements. The segregation of phosphorus and tin showed good correlation but the sulphur distribution in the film was distinctly different. The film formed was often thick, up to 20 μm. Such a film had poor lubricity and weak strength against shearing.     

On the relationship between the parameters of the electric response to pulsed mechanical exposure and the formation of cracks in concrete

The relationship between the parameters of acoustic emissions and the electric response to pulsed mechanical excitation of high-density concrete and the stages of deflected mode that is formed by external compressive loadings was studied. It was established that the attenuation coefficient of the electric-response energy increases considerably when a concrete sample passes from elastic deformation into the fracturing zone.     

Sensitivity of an optimized contour mask technique to errors in fabricating piecewise continuous relief diffractive optical elements

This paper considers the effect of errors in the technological process using an optimized contour mask technique for fabricating piecewise continuous relief diffractive optical elements on the reduction in the backward slopes of diffraction zones and the increase in the diffraction efficiency of the elements. The process parameter tolerances necessary for the implementation of the method are within the parameters of the standard microelectronic processes and equipment. The proposed method can be useful for laser writing systems and projection lithography that form the relief in a photoresist with a backward slope width exceeding 1 µm since it provides a significant improvement in the performance of the fabricated diffraction structures.     

Application of a data-driven monitoring technique to diagnose air leaks in an automotive diesel engine: A case study

This paper presents a case study of the application of a data-driven monitoring technique to diagnose air leaks in an automotive diesel engine. Using measurement signals taken from the sensors/actuators which are present in a modern automotive vehicle, a data-driven diagnostic model is built for condition monitoring purposes. Detailed investigations have shown that measured signals taken from the experimental test-bed often contain redundant information and noise due to the nature of the process. In order to deliver a clear interpretation of these measured signals, they therefore need to undergo a ‘compression’ and an ‘extraction’ stage in the modelling process. It is at this stage that the proposed data-driven monitoring technique plays a significant role by taking only the important information of the original measured signals for fault diagnosis purposes. The status of the engine's performance is then monitored using this diagnostic model. This condition monitoring process involves two separate stages of fault detection and root-cause diagnosis.The effectiveness of this diagnostic model was validated using an experimental automotive 1.9 L four-cylinder diesel engine embedded in a chassis dynamometer in an engine test-bed. Two joint diagnostics plots were used to provide an accurate and sensitive fault detection process. Using the proposed model, small air leaks in the inlet manifold plenum chamber with a diameter size of 2–6 mm were accurately detected. Further analyses using contribution to T² and Q statistics show the effect of these air leaks on fuel consumption. It was later discovered that these air leaks may contribute to emissions fault.In comparison to the existing model-based approaches, the proposed method has several benefits: (i) it makes no simplifying assumptions, as the model is built entirely from the measured signals; (ii) it is simple and straight-forward; (iii) there is no additional hardware required for modelling; (iv) it is a time and cost-efficient way to deliver condition monitoring (i.e. fault diagnosis application); (v) it is capable of pin-pointing the root-cause and the effect of the problem; and (vi) it is feasible to be implemented in practice.     

Investigating the formation of intermetallic compounds during friction stir welding of magnesium alloy to aluminum alloy in air and under liquid nitrogen

This research demonstrates the use of submerged friction stir welding under liquid nitrogen as an alternative and improved method for creating fine-grained welds, and hence, to alleviate formation of intermetallic phases. Magnesium alloy and aluminum alloy were joined by friction stir welding in two environments, namely air and liquid nitrogen, with 400 rpm rotation and 50 mm/min travel speed. The temperature profile, microstructure, scanning electron microscope energy dispersive X-ray spectroscopy analysis and hardness were evaluated. In the stir zone of air-welded specimen, formation of brittle intermetallic compounds causes the weld to crack. These phases were formed because of constitutional liquation. The stir zone of under liquid nitrogen-welded specimen showed that formation of intermetallic compounds is suppressed significantly because of lower heat input.     

Reduction in the service life due to an overload test of a metallic structure operated under corrosive conditions

The effect of an overloading test on the remaining service life of a metallic structure exposed to corrosion is discussed. Conditions of destruction during such tests have been determined. The reduction in the service life as a result of such tests is quite considerable, but, if an overloading test does not lead to destruction, the reduction in the service life is small.     

A Method for Evaluating Failure in Reinforced Concrete under Bending Based on the Response of Electrical Parameters to an Impact Action

The regularities of changes in the properties of the electrical response of reinforced concrete to an impact action in a four-point bending flexural test and the influence of the rebar cage configuration on the processes of failure in reinforced beams and on electrical response parameters have been studied. Criteria have been proposed for determining the stages of failure in reinforced concrete beams, based on electrical response parameters. The nucleation and growth of macrocracks in the tensile zones of reinforced beams is accompanied by a drop in the maximum cross-correlation coefficient of signal spectra at the current and previous loading levels to 0.45–0.6. An increase in the energy attenuation coefficient of electrical responses in a reinforced beam by 1.5–2.5 times can serve as a precursor to its impending catastrophic breakdown.     

Accessory allowing an optical cell of 6-10,000 microm path for liquids and gases to be filled in vacuum and used under pressure

An accessory for introducing liquid or gaseous samples without any contamination into an evacuated cell for optical spectrometry is described. The procedure for its use is similar to that of sample injection into a gas-liquid chromatograph, no glove box or glove bag being needed. Main benefits are the wide choice of size of the samples, their recoverability, safety, and a range of optical paths allowing to measure the absorbance of strongly absorbing liquids and gases, very dilute liquid solutions, and liquefied gases under moderate pressure. Short path spectra of gaseous water pressure standards consent quantification of water partial pressure measured in common gas cells.