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We formulate and solve the problem of biaxial bending of an isotropic plate with two coaxial through cracks of identical lengths by distributed bending moments applied at infinity under the action of external load symmetric about the cracks with regard for the contact zone of their faces and in the presence of plastic zones near the crack tips, where the Tresca plasticity conditions are satisfied in the form of a surface layer or a plastic hinge. By using complex potentials of the plane problem and the classical theory of bending of the plates, we obtain an analytic solution of the problem in the class of functions bounded in the vicinity of the vertices of the plastic zones. The length of the plastic zones and the crack-tip opening displacements are found numerically. [ABSTRACT FROM AUTHOR]

We study viscoelastic stresses in the plates containing inclusions weakened by cracks by the method of boundary integral equations and the Laplace integral transformation. The case in which the rheological relations between stresses and strains are written in the differential form is analyzed in detail. To solve the boundary problem of viscoelasticity, we use the well-known approach in which the corresponding problem of the theory of elasticity is studied by replacing the differential operators with constant quantities. The solution of the auxiliary problem is obtained by the method of boundary integral equations reduced to a system of algebraic equations. After replacing the elastic quantities in this system by the corresponding differential operators, we solve the system obtained as a result by using the Laplace integral transformation and then applying the improved numerical-analytic inversion formula adapted to this class of problems. [ABSTRACT FROM AUTHOR]

A two-stage model of propagation of fatigue mode I cracks in thin isotropic plates of finite size under uniaxial symmetric and asymmetric tension-compression is constructed based on an approach that combines the force concept of crack mechanics and the concept of continuous damage mechanics. The model is validated experimentally by determining the kinetics of growth of a fatigue crack under uniaxial reversed and repeated cyclic loadings. [ABSTRACT FROM AUTHOR]

A Rayleigh-Ritz solution approach for generally restrained multilayered variable angle tow stiffened plates in postbuckling regime is presented. The plate model is based on the first order shear deformation theory and accounts for geometrical nonlinearity through the von Kármán’s assumptions. Stiffened plates are modelled as assembly of plate-like elements and penalty techniques are used to join the elements in the assembled structure and to apply the kinematical boundary conditions. General symmetric and unsymmetric stacking sequences are considered and Legendre orthogonal polynomials are employed to build the trial functions. A computer code was developed to implement the proposed approach and to establish its applicability and its features for investigating variable angle tow structures. The proposed solution is validated by comparison with literature and finite elements results. Original results are presented for postbuckling of variable angle tow stiffened plates showing the potentialities of the method. [ABSTRACT FROM AUTHOR]

Abstract: Porous materials are widespread in different areas of technology, biology, medicine. Therefore, the study of mechanical behavior for different problems of poroelasticity is important. The present work is devoted to the development of a mathematical model for the deformation of porous plates. By completing this, the model of material with voids is used. To implement a plate behavior the plane stress and Kirchhoff hypotheses are introduced. Further realization is based on the variational principle, similar to the Lagrange one. As an example there constructed solutions for the cylindrical bending and in‐plane stretching problem of a porous plate. In addition, the bending problem in the case of a homogeneous disturbed surface load is analyzed in details with a demonstration of the boundary‐layer effect. [ABSTRACT FROM AUTHOR]

Elastic fields of twist disclinations in an anisotropic elastic plate are derived in the context of Kirchhoff’s plate theory. The solution is utilized to develop a new numerical method for general anisotropic cracked plates containing an arbitrary array of cracks under bending or twisting. Integral equations are constructed by simulating cracks as continuous distributions of disclinations. Using Gauss–Chebyshev integration formulas, the integral equations can be transformed into the form of algebraic equations, with which the disclination densities and the stress intensity factors associated with each crack tip can be computed. Numerical examples are provided for isotropic or orthotropic plates with one to three cracks. [ABSTRACT FROM AUTHOR]

This article deals with the computational modelling of the fatigue crack aspect ratio evolution in embedded, surface, and corner cracks located in finite-thickness plates under tensile fatigue. The approach is based on the Paris law for fatigue propagation and an expression for the stress intensity factor (SIF) provided by Newman and Raju. Numerical results indicate that the crack path develops in such a manner that all flaws tend to reach similar aspect ratios, i.e., a preferential crack path does exist along which there is a one-to-one relationship between the aspect ratio and the relative crack depth (a sort of master curve in the matter of fatigue crack path evolution). Such a reference curve corresponds to that of a very superficial initial flaw with almost circular shape. The convergence (quicker or slower approach between fatigue crack paths starting from different initial defects) is higher for surface flaws than for corner cracks, and quicker for the latter than for embedded discontinuities. Corner defects increase their size faster than surface cracks, and the latter do the same quicker than the embedded ones. [ABSTRACT FROM AUTHOR]

In this work, weld-repaired Bisplate80 joints without or with a buffer layer (BL) were subjected to a post-weld heat treatment (PWHT) at 930 °C for 1 h followed by air cooling. The mechanical properties and fracture mechanism of the PWHT specimens were compared to those from corresponding as-welded specimens to study the influence of the PWHT and to compare them with as-received Bisplate80 specimens to inspect the welding quality of the joints. Fatigue crack growth curves and micro-hardness profiles across the welded joints for the as-weld or PWHT conditions were measured together with relevant scanning electron microscope observations along the crack growth path. Special attention was paid to the areas at and around the welded interfaces. The results showed that the incorporation of a BL with an appropriate thickness significantly improved the fatigue crack growth behavior of the welded joint for the PWHT condition, as the d a/d N over the entire area of the welded joint was much lower than for both the as-welded and as-received Bisplate80 specimens, showing that the incorporated BL greatly improved the fracture mechanisms of the fatigue specimens. [ABSTRACT FROM AUTHOR]

Fatigue performance of butt welded splices in plates of different thicknesses (hereafter referred to as BWSPDT) was investigated in this paper. Fatigue tests were conducted on 26 specimens. Experimental S-N curve of 95% survival probability for BWSPDT was established based on 21 effective fatigue test data involving 7 stress levels. Both analytical and numerical fatigue crack propagation analysis were fulfilled. It was found that the numerical approach would provide a lower stress intensity factor (SIF) level than that obtained through the analytical approach, as the numerical approach can better reflect the relationship between the local crack development and the variation of the stress distribution of the whole structural details. The influences on fatigue life due to the variation of the size, shape and location of the initial crack were investigated. The calculation formula for the fatigue crack propagation life in terms of arbitrary initial crack between 0.075 mm and 0.4 mm was derived. For the fatigue crack propagation analysis for BWSPDT, a semi-circular crack with 0.075 mm initial depth locating at the center of the specimen was recommended to be adopted as the initial crack input when no detailed inspection information on initial flaws available. [ABSTRACT FROM AUTHOR]

Mechanical models have the potential to characterize the behavior of complex steel joints, using for that the isolated behavior of its components, assembled according to their geometry. However, the mechanical models implemented in the current design codes are not prepared to deal with cyclically loaded joints, due to the complexity associated to load reversal. To overcome this difficulty this work makes to use of detailed finite elements models, to extract the needed force-displacement components response. The FE models are capable of representing the various connections components and the several sources of nonlinearity associated to them and are validated against existing experimental data. The discretized nature of the FE models is able to provide all the relevant information of any element, and even provide data that is typically unavailable from experimental tests, such as the contact or friction forces. Several models of bolted end plate beam-to column joints, with partial-strength classification in relation to the connected beam, have been developed using the ABAQUS FE package. A methodology to extract the needed force-displacement relationships of the column web components of the joint is presented and applied to the joints, through integration of stress and displacement fields. The results, presented in this paper, allow setting the base for a component-based model to simulate the dissipative behavior of steel connections subjected to cyclic loading conditions. [ABSTRACT FROM AUTHOR]

Structural health monitoring is essential to maintain the structural integrity by predicting problems in an early time. This consequently could be reflected on extending the life time of structures. Nondestructive tests based on dynamic measures are usually fast and economic in detecting damages of structures. Various numerical techniques together with recording time histories are used for this purpose. This paper presents a numerical method for damage detection in plate-like structures. The modeling of damage was conducted commercially using the module of MatLab. Comparison of different mode shapes was used in the analysis to detect the location of local damage based on residual force vector. The technique utilized the node residual force vector to locate and evaluate the degree of the suspected damaged elements. In the current study, three configurations for plates were used. The study also concentrated on the efficiency of the new method in identifying damages of different degradation levels. The plates were subjected to different combinations of artificial damages applied at various positions on each plate. The study was not only able to identify the location but also the degree of damage in plates. It has been noted that identification of severe degradation was more precisely identified. As a result, the residual force method is the simplest damage quantification technique which approved to be accurate enough to be used in practical applications. [ABSTRACT FROM AUTHOR]

We consider the elasticity operator with zero Poisson ratio on an infinite strip and an infinite plate with a horizontal crack. We prove an asymptotic formula for the distance of the embedded eigenvalues to some spectral threshold of the operator as the crack becomes small. [ABSTRACT FROM AUTHOR]

Utilization of thin plates together with laser-based welding processes allows manufacturing of large weight efficient steel structures. However, the fatigue strength of welds in thin-plate structures with plate thicknesses below 5 mm is observed to have large variation, which brings challenges to fatigue strength assessment. One possible reason for this variation is the increased influence of actual weld geometry that is neglected in common fatigue strength assessment approaches utilizing geometry idealization. To reveal this influence the fatigue strength of 3 mm thick laser-hybrid welded butt joints were studied using the measured microscale weld geometry and the notch stress approach. Notch stresses were defined using Neuber’s stress averaging approach which allows the determination of the fatigue-effective stress without fictitious geometric modifications. For the studied specimens the large scatter of fatigue strength in the high-cycle region could be explained using this approach with high-resolution weld profile measurements combined with thorough finite-element analysis. It was observed that axial misalignment in narrow laser-hybrid welds causes a significant notch stress increase on the root side reducing the fatigue strength dramatically in terms of structural and nominal stress. In order to capture the increased notch stress it is crucial to use a significantly smaller stress averaging length than commonly assumed for welded joints. [ABSTRACT FROM AUTHOR]

This paper presents experimental and numerical study of the fatigue crack growth of hollowed pre-notched plates with multiple site damages (MSD). The numerical analyses were performed using finite element method. Experiments were carried out to validate the numerical results. Fatigue tests of aluminum sheets with MSD cracks were conducted to evaluate the effects of some parameters such as the thickness, hole diameter and central distance of the holes. The results show that the distance of the holes has greatest and size of the hole has little effects on the fatigue lives. Nucleation of cracks strongly depends on the thickness, distance and hole size. [ABSTRACT FROM AUTHOR]

In this study, experimental and numerical investigations were carried out in order to compare the performances of composite and metallic patches for repairing aircraft structures. In the experimental part, an accelerating aging of the composite was realized by the immersion of the composite patch in distilled water. The fatigue lives of notched plates repaired with aged composite patch, non-aged composite patch and aluminum patch were measured. The obtained results show that the composite patch is more beneficial than the aluminum patch if there is no significant water absorption by the composite. In the numerical part, the stress intensity factor at the crack tip was computed for aged and non-aged composite patches and for aluminum patches. The numerical results confirm the experimental ones, the reduction of the stress intensity factor by the composite patch is more significant than the aluminum patch but the water absorption reduces significantly the repair efficiency. [ABSTRACT FROM AUTHOR]

We formulate a mathematical model for the determination of the effect of hydrogen on the period of initiation of creep-fatigue macrocrack in the vicinity of a stress concentrator in a plate. By using this model, we find the period of initiation of a macrocrack for a strip with two side notches under cyclic loads, high temperatures, and the action of hydrogen-containing medium. It is shown that hydrogen increases the rate of crack initiation in steel plates. [ABSTRACT FROM AUTHOR]

Fiber-reinforced polymer (FRP) overlays have been successfully used in the aerospace industry to repair fatigue damage in aluminum plates. With this success there is potential for use of similar FRP overlays to repair fatigue damage in aging steel bridge structures. This study investigated the effectiveness of repairing fatigue damage in steel plate with adhesively bonded carbon fiber-reinforced polymer (CFRP) overlays. A total of 15 steel plate specimens with preexisting fatigue cracks were repaired with varying thicknesses of CFRP overlays to evaluate the effect of the ratio of axial stiffness of the composite to that of the underlying steel, the axial stiffness ratio (SR), on increased fatigue life and decreased applied stress. The results showed that increasing the axial stiffness ratio from 0 to 0.4 could increase the fatigue life by a factor of 10 for the most extreme conditions, and with an optimal axial stiffness ratio infinite fatigue life may be reached. Fatigue life of the steel specimens in this study was found to be dependent on both axial stiffness and applied stress range. Results from finite-element analyses validated the use of axial stiffness as a design parameter and correlated to the experimental results discussed. [ABSTRACT FROM AUTHOR]

Abstract: A recently more used method of improving weld quality at the weld transition to the plate called HFMI (High Frequency Mechanical Impact) has been investigated and tried on two demonstrators, a bogie beam in an articulated hauler and a dipper arm in an excavator, see fig. 1. The designs of the beams have been made so that thinner plates can be used and higher material strength can be utilized. Such an approach needs to make use of local based analysis methods and in this case the effective notch method was used. Recently made research has suggested SN-curves where the use of HFMI in combination with different material yield strengths are described and these FAT values have been used to develop allowed stress levels in the beams to fulfill the life requirements. All this resulted in components which were 24% and 18% lighter using plate thicknesses of 8-12mm in material yield 700MPa. They were then produced and tested in a rig to verify the designs. The results imply that the HFMI treatment is a very promising method to build lighter welded structures, however, the design needs to take some new considerations into account to succeed. [Copyright &y& Elsevier]

ABSTRACT Welded steel connections of infrastructures are susceptible to fatigue failure. Advanced carbon fibre reinforced polymer (CFRP) has been demonstrated promising for fatigue strengthening of steel structures. Limited research was conducted on CFRP strengthening of welded connections. This paper focuses on the application of ultra high modulus (UHM) CFRP plates with a modulus of 460 GPa to strengthen steel plates with longitudinal fillet weld attachment using five CFRP strengthening configurations. A series of fatigue tension tests were carried out with constant amplitude fatigue loading. Beach marking technique was adopted to record the crack propagation process. Effects of CFRP bond length, bond width and bond locations on fatigue performance of welded steel joints were investigated. The experimental results showed that UHM CFRP plates could generally increase the fatigue life of the welded steel joints. It seems better to apply CFRP on the welding side of the specimen to achieve longer fatigue life. Then, the effects of weld and weld attachment on the CFRP strengthening efficiency was further studied by comparing experimental results of non-welded steel plates with single side UHM CFRP plate strengthening. Finally, the classification method was adopted to assess the strengthening efficiency of the UHM CFRP plate to the steel plates with longitudinal weld attachment. [ABSTRACT FROM AUTHOR]

A mathematical model for studying the fatigue fracture of thin-walled structural elements (plates) with cracks under block loading is formulated. The influence of the form and structure of loading blocks on the residual lifetime of a plate is investigated. [ABSTRACT FROM AUTHOR]

Welding tests were conducted using the flux-cored arc welding method on a plate made from duplex steel, grade UNS S31803, thickness of 9.5 mm with the increased 10 mm root gap. An analysis of fatigue strength was carried out, using the finite element method, on butt joints which underwent axial tension. Experimental research of fatigue strength was conducted. The influence of welding, with various root gaps, on fatigue strength was determined. A fractographic analysis of selected samples, after fatigue strength examinations, was executed. It was proven that the increase of the root gap has an influence on a decrease in fatigue resistance; however, it fulfils the requirements prescribed by Det Norske Veritas rules. [ABSTRACT FROM PUBLISHER]

Carbon fibre reinforced polymer (CFRP) has shown promise for improving the fatigue performance of steel structures. Previous studies have indicated that increasing the Young's modulus of CFRP can be beneficial for decreasing the stress intensity factor at the fatigue crack tip. In this project, ultra high modulus (UHM) CFRP plates with Young's modulus of 460 GPa were adopted to study their fatigue repair effectiveness. A series of fatigue tension tests was carried out on steel plates with an initial crack in the centre. Five strengthening configurations were used and a constant amplitude fatigue loading was applied to all the specimens. The beach marking technique was utilized to record the fatigue crack propagation. The effects of CFRP bond length, bond width and bond locations on the fatigue performance of cracked steel plates were also studied. The experimental results show that UHM CFRP plates can greatly increase the fatigue life of cracked steel plates by a factor ranging from 3.26 to 7.47. When CFRP plates cover the whole crack surface, the fatigue crack of the steel plate is arrested. The strengthening effectiveness of UHM CFRP plates is also compared with those using high Young's modulus CFRP sheeting and normal Young's modulus CFRP plates with or without prestressing. [ABSTRACT FROM AUTHOR]

Abstract: This paper describes the effect of contact forces on the fretting fatigue behavior of bolted plates. Both fretting fatigue experiments and numerical simulation with FEM and SEM/EDS observations and analysis were carried out. With the increase of contact forces, the sites of crack initiation change from the edge of the central hole to close the border of contact and the fretting fatigue life increases. The local stresses and the relative displacement in the contact zone are two principal factors which influence the fretting fatigue behavior. A Map of Material Response (MMP) was determined basing on obtained results can describe the behavior of the fretting fatigue damage and predict the conditions which conduct to cracking initiation and propagation. [Copyright &y& Elsevier]

Abstract: Impedance-based damage detection techniques gained popularity among structural health monitoring (SHM) and nondestructive testing (NDT) communities due to their sensitivity to local damage and applicability to complex structures. In general, conventional impedance-based techniques identify damage by comparing “current” impedance signals with “baseline” ones obtained from the pristine condition of a structure. However, in-situ structures are often subject to changing temperature and loading conditions that can adversely affect measured impedance signals and cause false-alarms. In this paper, a “reference-free” impedance method, which does not require direct comparison of the current impedance signals with the previously obtained baseline impedance signals, is developed for crack detection in a plate-like structure. The proposed technique utilizes a single pair of PZTs collocated on the opposite surfaces of a structure to extract mode conversion produced by crack formation. Then, a reference-free damage classifier is developed and performed on the extracted mode conversion for instantaneous damage diagnosis. Numerical simulations and experimental tests have been conducted explicitly considering varying temperature and loading conditions to demonstrate the robustness of the proposed damage detection technique under varying operational and environmental conditions. [Copyright &y& Elsevier]

Thermoelastic data are combined with an Airy stress function to determine the individual stresses on and near the boundary of a circular hole which is located below a concentrated edge-load in a plate. Coefficients of the stress function are evaluated from the measured temperatures and the local traction-free conditions are satisfied by imposing $$ {\sigma_{r{\rm{r}}}} = {\tau_{r\theta }} = 0 $$ analytically on the edge of the hole. The latter has the advantage of reducing the number of coefficients in the stress function series. The method simultaneously smoothes the measured input data, satisfies the local boundary conditions and evaluates individual stresses on, and in the neighbourhood of, the edge of the hole. Attention is paid to how many coefficients to retain in the stress function series. Although the presence of high stress concentration factors, together with a hole-diameter-to-plate-thickness ratio of only two, result in some three-dimensional effects, these are relatively small and the agreement between the thermoelastic values, those from recorded strains and FEM-predicted surface stresses is good. [ABSTRACT FROM AUTHOR]

The objective of this work was to study the influence of the boundary conditions on low-velocity impact behaviour of carbon-epoxy composite plates. Experimental work and numerical analysis were performed on [0,90] laminates. The influence of different boundary conditions on the impacted plates was analysed considering rectangular and square plates. The X-radiography was used as a non-destructive technique to evaluate the internal damage caused by impact loading. A three-dimensional numerical analysis was also performed considering progressive damage modelling. The model includes three-dimensional solid elements and interface finite elements including a cohesive mixed-mode damage model, which allows simulating delamination between different oriented layers. It was verified that plate's boundary conditions have influence on the delaminated area. Good agreement between experimental and numerical analysis for shape, orientation and size of the delamination was obtained. [ABSTRACT FROM AUTHOR]

Abstract: The present paper describes a first-order analytic model of the breach of monolithic glass plate subject to impact by chunky projectiles. The purpose of the model is to provide a theoretical framework for examining the consequences of the impact breach experiments of Sun et al. [Sun X, Khaleel MA, Davies RW. Modeling of stone-impact resistance of monolithic glass ply using continuum damage mechanics. Int J Damage Mech 2005;14:165–78]. A failure criterion of the Tuler–Butcher form [Tuler FR, Butcher BM. A criterion for the time dependence of fracture. Int J Fracture Mech 1968;4:431–7] is used with the model. The experimental impact breach experiments joined with the analytic model demonstrate time-dependent failure and lack of replica scaling for the present data. Methods are explored for the assessment of fragmentation resulting from the impact breach of brittle materials. [Copyright &y& Elsevier]

An improved higher-order shear deformation theory of plates is presented in this paper. The theory is developed from the transverse shear deformation theory presented by Ambartsumian [11]. The present plate theory contains kinematics of higher-order displacement field of plates, a system of higher-order differential equilibrium equations in terms of the three generalized displacements of bending plates, and a system of boundary conditions at each edge of plate boundaries. The present shear deformation theory of plates is validated by applying it to solve torsional plates and simply supported plates. The obtained solutions using the present theory are compared with the solutions of other shear-deformation theories. A good agreement is achieved through these comparisons and the advantages of the present theory are clearly verified. The shear deformation plate theory presented here can be applied to the analysis of laminated composite plates to better predict their dynamic and static behaviors. The proposed theory should also be supplemented to the theory of finite element analysis for developing new shell elements. [ABSTRACT FROM AUTHOR]

In the present work, the influence of strain rate on the collapse modes, the crushing mechanisms and the energy absorption characteristics of four types of composite sandwich panels was investigated in a series of impact and static in-plane tests. The tested sandwich specimens were formed combining two types of glass fibre reinforced plastic (FRP) faceplate laminates with three types of polymer foam core (poly-methacryl-imide (PMI) foam and two grades of cross-linked poly-vinyl chloride (PVC) foam) in four different material combinations. Three modes of collapse were observed in the series of impact and static compression tests, but only one of them - which was observed only at higher strain rates - was a stable mode featuring progressive end-crushing of the sandwich panel and significant crash energy absorption. The analysis of the test results showed that the increase of the strain rate influenced significantly the mode of collapse of the tested sandwich panels and some of their energy absorption characteristics such as the critical load for failure initiation and the peak collapse load. Apart from the strain rate effects, the analysis of the test works focused on the mechanics of progressive deformation and crushing related to each mode of collapse and the influence of significant parameters of the sandwich panel construction - such as the properties of the foam core and the faceplates - on the overall crushing response and the energy absorption characteristics. [ABSTRACT FROM AUTHOR]

The problem of bifurcational instability of rectangular plates made of fibrous composite materials with reinforcement subject to long-term damage is formulated and solved [ABSTRACT FROM AUTHOR]

An experimental and analytical study was conducted to investigate the fatigue behavior of tension steel plates strengthened with prestressed carbon-fiber-reinforced polymer (CFRP) laminates. A simple fracture mechanics model was proposed to predict the fatigue life of reinforced specimens. Double-edge-notched specimens were precracked by fatigue loading and then strengthened by CFRP laminates at different prestressing levels. The effects of the applied stress range, CFRP stiffness, and prestressing level on the crack growth were investigated. Experimental results show that the increase of the prestressing level extends the fatigue life of a damaged steel plate to a large amount. The CFRP with the highest prestressing level performed best, prolonging fatigue life by as much as four times under 25% higher fatigue loading. Theoretically, predicted results were in a reasonable agreement with the experimental results. A parametric analysis was also performed to investigate the effects of the applied stress range and the prestressing level on the debonding behavior of the adhesive and on the secondary crack propagation. [ABSTRACT FROM AUTHOR]

Purpose - The purpose of this paper is to demonstrate by experiments that non-linear Lamb wave modulation spectrum (NLWMS) will be a good indicator of fatigue cracks in a metallic plate. Design/methodology/approach - A system composed of piezoelectric transducers, arbitrary waveform generator, power amplifier, laser vibrometer, digital oscilloscope and computer has been constructed, and using this system, three samples made of 7075-T6 aluminium alloy plates are studied, respectively. One is with a fatigue crack, one is with a through hole and the other is intact. Findings - The experimental results show that there are no significant harmonics and sidebands in the intact sample, and there are no modulation frequencies in the drilled-hole sample. On the contrary, in the cracked sample, there is an abundance of the harmonics and sidebands. Therefore, these new modulation frequency components can be used to indicate the presence of the fatigue crack. Practical implications - This paper will provide a method for detecting fatigue crack in metallic plates, especially aluminium alloy plates for aerospace applications. Originality/value - Under the excitation of two different frequency Lamb waves, experiments on 7075-T6 alloy plates show that new rising modulation frequency components can be used to indicate the presence of the crack. So, the fatigue crack in metallic plates can be detected by NLWMS. [ABSTRACT FROM AUTHOR]

This paper describes a series of tests on Carbon Fiber Reinforced Polymers (CFRP) sheet bonded steel plates. The specimens were tensioned to failure after enduring a pre-set number of fatigue cycles at various load ratios (defined as the ratio of the maximum load in the fatigue test to the corresponding static strength). The aim of the study is to investigate the effect of fatigue loading on bond strength and failure modes. Both normal modulus (E = 240 GPa) and high modulus (E = 640 GPa) CFRP sheets were used in the tests. The experimental results were compared with those for specimens subjected to static tension alone. It was found that the failure modes of the CFRP-sheet bonded steel plates were not affected greatly by the fatigue loading except for those bonded with high modulus CFRP, where fiber fracture extended over more than one cross-section. The fatigue loads appear to have less effect on the bond strength of high modulus CFRP-sheet bonded steel plates. Reduction in bond strength from 10% to 20% was observed for normal modulus CFRP-sheet bonded steel plates when the load ratio is less than 30%. [ABSTRACT FROM AUTHOR]

Fracture mechanics is an important tool in measuring the mechanical performance of materials and components. It applies the theories of elasticity and plasticity to the microscopic crystallographic defects found in real materials in order to predict the macroscopic mechanical failure of bodies. Fracture mechanics uses methods of analytical solid mechanics to calculate the driving force on a crack and those of experimental solid mechanics to characterize the material's resistance to fractures. The objective of this paper is to develop an automated macro suitable for through cracked and double edge cracked plates and to verify its compatibility with the theoretical computations based on standard theorems of fracture mechanics. A comparison is also made for the stress intensity parameters like stress intensity based on the finite element method and the life of the structure, using numerical simulation of fatigue crack growth. [ABSTRACT FROM AUTHOR]

This paper outlines the experimental research conducted by the authors to highlight the efficiency of postwelding application of the ultrasonic impact treatment (UIT) on fillet welded lap joints in case of metal constructions subject to variable operating stress. The series of experiments consisting in fatigue testing specimens extracted from test-plates presenting fillet welded lap joints, subject and respectively not subject to post-welding UIT, led to the conclusion that increased fatigue behavior performances under UIT is relatively low by reference to the increased construction costs generated by the application of such a treatment. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents a new method based on curvelet transform to assess damage location in plate structures. The curvelet transform was developed over the last few years in an attempt to overcome inherent limitations of traditional multiscale representations such as wavelets. In this research, curvelet transform has been employed due to its favorable performance in detecting line feature. The formulation of discrete curvelet transform using unequally-spaced fast Fourier transforms for plate damage detection was investigated. The proposed method was applied to a four-fixed supported rectangular plate containing one or two damages with arbitrary length, depth and location. Thereafter, the damage was detected in the plate using the proposed method. By way of comparison between location obtained from the proposed method and simulation model, it was concluded that the method is sensitive to damage. Moreover, the performance of the method has been verified through using experimental modal data of a plate. [Copyright &y& Elsevier]

Abstract: In this research the effect of bolt interference fit on the fatigue life of lap joints in double shear was investigated by conducting experimental fatigue tests and also analytically by FE simulation. In the experimental part, fatigue tests were carried out on specimens made from aluminium alloy 2024-T3 plates joined together as double lap joints and secured using bolts having fits ranging from zero clearance to different levels of interference. The results demonstrate how the failure is affected using different levels of interference fit. In the numerical study, 3-D FE models were used to simulate the different pin in hole fits considered and the results have been used to help explain the trends which were observed in the experimentally obtained S–N curve behaviour. [Copyright &y& Elsevier]

Abstract: This paper addresses the effect of a local quasi-static indentation or a low-velocity impact on the residual strength of foam core sandwich panels subjected to edgewise compression. The damage is characterized by a local zone of crushed core accompanied by a residual dent in the face sheet. Experimental studies show that such damage can significantly alter the compressive strength. Theoretical analysis of the face sheet local bending is performed for two typical damage modes (with or without a face–core debonding). The solutions allow estimation of the onset of (a) an unstable dent growth (local buckling) or (b) a compressive failure in the face sheet. The theoretical results are in agreement with the test data for two considered sandwich configurations. [Copyright &y& Elsevier]

Abstract: The use of adhesively-bonded composite materials has lead to great advances in repairing and strengthening cracked or aged metallic structures. However, less is known about the fatigue performance of the bonding between the composites and the metallic substrate, which is the deciding factor when designing the strengthening. In this study, a series of experiments is performed to investigate the effectiveness of the composites on preventing fatigue crack propagation and extending the fatigue life of steel plates. The composite material of CFRP sheet is adopted. Both single-sided and double-sided repairs are studied. Experimental results show that the application of composite patches substantially reduces crack growth rate and prolong fatigue life. The double-sided repair scheme increased the fatigue life by 2.2–2.7 times over un-patched steel plates when normal modulus CFRP sheets were used, and by 4.7–7.9 times when high modulus CFRP sheets were used. The CFRP sheets with high modulus were found to be much more efficient. Bond width has considerable influence on the crack growth life. These two findings were especially true for double-sided repairs. The parameters of patch thickness, patch length and patch configuration, had an influence on fatigue life increase of over 20% for both single-sided and double-sided repairs, except that patch configuration had only a 6% influence on fatigue life increase for double-sided repairs. Furthermore these three parameters had slightly more influence on single-sided repairs than on double-sided repairs. [Copyright &y& Elsevier]

Abstract: Basing on the First-order Shear Deformation Theory (FSDT), this paper focuses on the dynamic behaviour of moderately thick functionally graded parabolic panels and shells of revolution. A generalization of the power-law distribution presented in literature is proposed. Two different four-parameter power-law distributions are considered for the ceramic volume fraction. Some symmetric and asymmetric material profiles through the functionally graded shell thickness are illustrated by varying the four parameters of power-law distributions. The governing equations of motion are expressed as functions of five kinematic parameters. For the discretization of the system equations the Generalized Differential Quadrature (GDQ) method has been used. Numerical results concerning four types of parabolic shell structures illustrate the influence of the parameters of the power-law distribution on the mechanical behaviour of shell structures considered. [Copyright &y& Elsevier]

Abstract: In the present article, axisymmetric bending and stretching of functionally graded (FG) circular plates subjected to uniform transverse loading based on fourth-order shear deformation plate theory (FOST) have been studied. Using a fourth-order shear deformation theory, the solutions for deflection and rotation functions of FG plates are presented in terms of the corresponding quantities for a homogeneous plate using the classical plate theory (CPT), from which solutions one can easily obtain the FOST solutions for axisymmetric bending of FG circular plates. It is assumed that the effective mechanical properties of the functionally graded plates through the thickness are continuous functions of the volume fractions of the constituent parts which are themselves defined by a power-law function. Numerical results for maximum deflection and shear stress are presented for various percentages of ceramic–metal volume fractions. These results are also compared with those obtained from the first-order shear deformation plate theory of Mindlin (FST), the third-order shear deformation plate theory of Reddy (TST) as well as the exact three-dimensional elasticity solution. It is found that although the maximum deflections obtained using FOST and TST are close to each other, the through-thickness shear stress is predicted more accurately by the FOST formulation than by the TST. [Copyright &y& Elsevier]

Abstract: Based on Mindlin''s plate theory, free vibration analysis of moderately thick shear deformable annular functionally graded plate coupled with piezoelectric layers is presented in this paper. A consistent formulation that satisfies the Maxwell static electricity equation is presented so that the full coupling effect of the piezoelectric layer on the dynamic characteristics of the annular FGM plate can be estimated based on the free vibration results. The differential equations of motion are solved analytically for various boundary conditions of the plate through the transformation of variable method. The applicability of the proposed model is analyzed by studying the effect of varying the gradient index of FGM plate on the free vibration characteristics of the structure. For some specific cases, obtained results were cross checked with those existing literatures and furthermore, verified by those obtained from three-dimensional finite element (3D FE) analyses. [Copyright &y& Elsevier]

Abstract: This paper investigates the dynamic pull-in behavior of microplates actuated by a suddenly applied electrostatic force. Electrostatic, elastic and fluid domains are involved in modeling. First-order shear deformation plate theory and classical plate theory are used to model the geometrically nonlinear microplates. The equations of motion are descritized by the finite element method. The effects of nonlinearity, fluid pressure, initial stress and different geometric parameters on dynamic behavior are examined. In addition, the influences of initial stress and actuation voltage on oscillatory behavior of microplates are evaluated. [Copyright &y& Elsevier]

Abstract: This paper provides a probabilistic formulation to design a monitoring setup for damage detection in piezoelectric plates, solving a model-based identification inverse problem (IP). The IP algorithm consists on the minimization of a cost functional defined as the quadratic-difference between experimental and trial measurements simulated by the finite element method. The motivation of this work comes from the necessity for a more rational design criteria applied to damage monitoring of piezoelectric materials. In addition, it is very important for the solving of the inverse problem to take into account the random nature of the system to be solved in order to obtain accurate and reliable solutions. In this direction, two investigations are considered. For the first, the experimental measurements are simulated combining a finite element and a Monte Carlo analysis, both validated with already published results. Then, an uncertainty analysis is used to obtain the statistical distribution of the simulated experimental measurements, while a sensitivity analysis is employed to find out the influence of the uncertainties in the model parameters related to the measurement noise. Upon the study of the measurements, they are used as the input for the damage identification IP which produces the location and extension of a defect inside a piezoelectric plate. For the second investigation, a probabilistic IP approach is developed to determine the statistical distribution and sensitivities of the IP solutions. This novel approach combines the Monte Carlo and the IP algorithm, considering the trial measurements as random. In conclusion, the analysis demonstrates that in order to improve the quality of the damage characterization, only a few material parameters have to be controlled at the experimental stage. It is important to note that this is not an experimental study, however, it can be considered as a first step to design a rational damage identification experimental device, controlling the variables that increase the noise level and decrease the accuracy of the IP solution. [Copyright &y& Elsevier]

Abstract: Butt welds are important connections for the integrity of most types of welded structures. In this paper some of the work that provides a basis for stress concentration factors for butt welds in plated structures, tubular sections, foundation piles, pipelines and shell structures is assessed. Eccentricities at plate thickness transitions and with fabrication tolerances give increased hot spot stress due to local bending when the plates are subjected to in-plane loading. This paper includes improved equations for stress concentration factors for girth butt welds in tubulars based on calibration with numerical data obtained from axisymmetric finite element analyses. In addition it includes recommendations on stress concentration factors to be used in fatigue design rules and for fatigue assessment of plated structures, tubular sections of different diameter to thickness ratios, foundation piles and pipelines. [Copyright &y& Elsevier]

Abstract: Plastic anisotropy of the as-rolled 7050 aluminum alloy plate was investigated by tensile tests conducted at different temperatures (340 and 460°C) and different strain rates of 1.0×10−4, 1.0×10−2, 0.1, and 1s−1. The results show that the plastic strain ratio of the as-rolled 7050 aluminum alloy plate deformed at 340°C is not sensitive to strain rate, which increases with increasing strain rate when the alloy was deformed at 460°C. Alloy elements of the alloy deformed at 460°C and different strain rates are in solution. The plastic strain ratio of the alloy deformed at 460°C was affected by texture components, especially the Brass orientation {011}〈211〉. Dynamic precipitation appears when the alloy was deformed at 340°C and different strain rates, and the alloy deformed is in over aged condition. Microstructure is the main influence of plastic anisotropy of the alloy deformed at 340°C. [Copyright &y& Elsevier]