Propagation of harmonic Lamb waves in plates made of functionally graded materials (FGM) with transverse inhomogeneity is studied by combination of the Cauchy six-dimensional formalism and matrix exponential mapping. For arbitrary transverse inhomogeneity a closed form implicit solution for dispersion equation is derived and analyzed. Both the dispersion equation and the corresponding solution resemble ones obtained for stratified media. The dispersion equation and the corresponding solution are applicable to media with arbitrary elastic (monoclinic) anisotropy.

In this study, the aerodynamic characteristics of a vertical-axis wind turbine blade coupled with a high-lift device, such as the Gurney flap at the trailing edge, are investigated. For numerical analysis, the force element theory is used to understand how the Gurney flap influences the force evolution of the lift-type vertical-axis wind turbine. This study shows that the lift and drag can be respectively approximated into four elements, which are induced by volume vorticity, rotational velocity, angular acceleration and surface friction of the flow around the blades. Based on the perspective of the force element theory, the present simulation provides a clear picture of how the Gurney flap influences the formation of the aerodynamic force elements during a rotational cycle for a vertical-axis wind turbine. Simulation results show that the contributions mainly result from the surface vorticities, the rotational acceleration of the airfoil, and the acceleration of the surface.

The problem of semi-infinite crack situated in an orthotropic strip sandwiched between two identical half planes has been considered. The considered boundary value problem has been solved to convert it into the standard Wiener-Hopf equation by using Fourier transform technique, which has been solved to obtain analytical expressions for stress intensity factor and crack opening displacement. The variations of stress intensity factors and crack opening displacement are displayed graphically for different pair of orthortropic materials and for various depth of the strip of the composite media.

The article deals with the modeling of stiffness properties of the rotors flange joints, which largely determine overall dynamics. Research is conducted on the example of the standard compressor shaft flange connection and the disk of the high-pressure turbine in the gas generator of the gas turbine engine (GTE). It is noted that the bending stiffness of the flange connection is a nonlinear function of the bending moment, whose both experimental and analysis magnitude is related to the rotor deflection from the unbalanced forces. It is shown that the value of the bending stiffness essentially depends not upon the flange connection geometry but on the bolts tightening force, the axial force, the tensile joint, the contact strain of the flange surfaces. Analysis of the effect obtained in different models of the flange connection of the bending stiffness values on the overall dynamics of the rotor showed the necessity of taking into account the entire set of factors acting in the joint.

In this paper, a novel continuous fiber reinforced piezoelectric composite (CFRPC) actuator is proposed to improve the stability and reliability of piezoelectric actuators. A piezoelectric driving structure composed of a cantilever beam and the CFRPC actuator is utilized to research the actuation performance of the CFRPC actuator. The expression of the equivalent moment for the CFRPC actuator is obtained using the equivalent load method and electro-mechanical coupling theory. Based on Euler-Bernoulli beam theory, the analytical expression of the deflection for the cantilever beam is derived. The accuracy of the obtained analytical expressions is demonstrated by finite element simulation as well as published experimental results. The actuation performance of the CFRPC actuator is investigated through the analytical expressions of the equivalent moment and deflection. The results show that the key parameters such as driving voltage, fiber volume fraction, cantilever beam height, actuator height, actuator length and actuator position have great influence on the actuation performance of the CFRPC actuator. The CFRPC actuator has good mechanical and electrical properties, and has a wide application prospect in the field of structural shape control.

The prediction of crack propagation is an important engineering problem. In this work, combined with triangular plane stress finite elements, a new remeshing algorithm for crack opening problems was developed. The proposed algorithm extends the crack iteratively until a threshold maximum crack length is achieved. The crack propagation direction is calculated using the maximum tangential stress criterion. In this calculation, in order to smoothen the stress field in the vicinity of the crack tip, a weighted average of the stresses of the integration points around the crack tip is considered. The algorithm also ensures that there are always at least eight elements and nine nodes surrounding the crack tip, unless the crack tip is close to a domain boundary, in which case there can be fewer elements and nodes around the crack tip.

Four benchmark tests were performed showing that this algorithm leads to accurate crack paths when compared to findings from previous research works, as long as the initial mesh is not too coarse. This algorithm also leads to regular meshes during the propagation process, with very few distorted elements, which is generally one of the main problems when calculating crack propagation with the finite element method.

In forming procedure of the micro grooves in the flat micro-groove heat pipe, the tie rod is often observed to be broken and the multi-tooth cutter is damaged due to the sharp increase of the ploughing-pulling pressure. This paper theoretically analyzes the factors affecting the capillary heat transferring limit of the micro-groove heat pipe, and simulates the machining process using finite element to acquire the best processing parameters: the squeeze angle is 120°, the drawing depth is 0.25mm, and the ploughing-pulling velocity is 100mm/s. Then these parameters are verified by real manufacturing experiments. The experimental results show that the ploughing-pulling pressure of the micro-groove forming process is close to the strength limit of the rod or multi-tooth cutter, and the process makes little swarf during work. Thus, only using the appropriate machine tool parameters, forming parameters and forming methods can make the wicking structure of flat micro-groove micro-heat pipe with the best heat transferring performance.

Finite element analysis is carried out to investigate the characteristics of Rayleigh, Sezawa and Love surface acoustic modes travelling along c-axis tilted ZnO layer on Si (001) half-space. The phase velocity dispersion curves, electromechanical coupling, reflectivity and mass loading sensitivity are studied for different electroacoustic coupling configurations and c-axis tilt angles θ. The behavior of Rayleigh and Sezawa modes operating as gas sensor, was simulated under the hypothesis that the ZnO free surface is covered with a thin polyisobutylene (PIB) film, 0.2 μm thick, able to selectively adsorb volatile gases at atmospheric pressure and room temperature. The sensor sensitivity to gas concentration in air, i.e. the frequency shifts per unit gas concentration, is studied and compared to some common materials used in literature. The obtained results, demonstrate the feasibility of high-frequency multimode micro-sensor based on the c-axis tilted ZnO piezoelectric thin film and operating in both liquid and gaseous environments.

The three dimensional standard damage model developed by Lavedeze et.al [9, 13] for uni-directional fibre reinforced ply is implemented into the nonlinear solution of NX Nastran within composite solid element to analyze the progressive damage process and ultimate failure of fibre reinforced composite laminates. This ply level meso-damage-constitutive-model takes into account main damage mechanisms including fibre breaking, matrix transverse cracking, and fibre/matrix de-bonding; also considers contributions like plasticity coupling, damage delay effects, and elastic nonlinearity in fibre compression. Dissipated energy and damage status are also introduced to reflect the damage condition on the macrostructural-level. Using the implemented code, simulation is carried out on the uniaxial tension of a [±45]2s laminate with IM6/914 material, wherein the predicted ply shear rupture stress matches the experimental results very well and better than the theoretical predictions in literature. Moreover, a [-45/0/45/90] holed laminate loaded in tension is simulated to show the complex behavior of subcritical damage evolution and failure process in the composite structure. The composite solid element with damage model supported in NX Nastran is shown to be a reliable tool to analyze the progressive failure of uni-directional fibre reinforced composite laminates.

The objective of this work is to computationally investigate the impact of an incidence-tolerant rotor blade concept on gas turbine engine performance under off-design conditions. When a gas turbine operates at an off-design condition such as hover flight or takeoff, large-scale flow separation can occur around turbine blades, which causes performance degradation, excessive noise, and critical loss of operability. To alleviate this shortcoming, a novel concept which articulates the rotating turbine blades simultaneous with the stator vanes is explored. We use a finite-element-based moving-domain computational fluid dynamics (CFD) framework to model a single high-pressure turbine stage. The rotor speeds investigated range from 100% down to 50% of the designed condition of 44,700 rpm. This study explores the limits of rotor blade articulation angles and determines the maximal performance benefits in terms of turbine output power and adiabatic efficiency. The results show articulating rotor blades can achieve an efficiency gain of 10% at off-design conditions thereby providing critical leap-ahead design capabilities for the U.S. Army Future Vertical Lift (FVL) program.

To evaluate the thermal deformation induced by 3D Printing (Three Dimensional Printing) process, a novel meshless analysis procedure is established. To account for the heat transfer and solidification effects of each printing layer from liquid to solid phase transition, the layer temperature is measured by the implanted thermocouples. Based on the temperature variation measured, the printing layer temperature can be averaged and considered as uniform for thermal analysis. In addition, as observed by the deformation of the printed target through experiment, only linear thermal elastic analysis is performed.

A rigorous algorithm for simulating the 3D Printing process is presented herein. Since the interpolation functions are no longer polynomials, a simple integration scheme using uniform integration points is applied to calculate the global stiffness matrix. Thus, the density and location of the integration points can be easily adjusted to fulfill the required accuracy. Further, for practical implementation, the simulation is also carried out by the concept of equivalent layer.

Demonstrative cases of printing a rectangular PLA (Polylactic Acid) brick are tackled to prove the accuracy and efficiency of the proposed meshless analysis procedure. The effects of layer thickness, equivalent layer and slenderness ratio on the thermal deformation of the printed brick are also investigated.

An elastic-plastic B spline finite strip method is proposed to investigate the continuous plate straightening process in this paper. First, the B spline displacement function that satisfies the boundary conditions of simply supported end and free end of the strip element is established, and then the stress-strain matrix is established. Second, the set method of total stiffness matrix based on B spline finite strip method for plate straightening problem is proposed, and the influence of nodal line number and strip elements number on the sparsity of total stiffness matrix is analyzed. Third, the loads on the strip elements are taken as linear uniform distribution, and the transformation matrix between the equivalent linear load and the actual load of the strip element is established. At last, the plate straightening simulation of 11 rolls straightening machine is made based on the elastic-plastic B spline finite strip method, the calculated results agree with the measured results, which approves that the elastic-plastic B spline finite strip method established can be applied to the plate straightening process.

Structural integrity plays an important role in any industrial activity, due to its capability of assessing complex systems against sudden and unpredicted failures. The work here presented investigates an unexpected new mechanism occurring in structures subjected to monotonic and cyclic loading at high temperature creep condition. An unexpected accumulation of plastic strain is observed to occur, within the high-temperature creep dwell. This phenomenon has been observed during several full inelastic finite element analyses. In order to understand which parameters make possible such behaviour, an extensive numerical study has been undertaken on two different notched bars. The notched bar has been selected due to its capability of representing a multiaxial stress state, which is a practical situation in real components. Two numerical examples consisting of an axisymmetric v-notch bar and a semi-circular notched bar are considered, in order to investigate different notches severity. Two material models have been considered for the plastic response, which is modelled by both Elastic-Perfectly Plastic and Armstrong-Frederick kinematic hardening material models. The high-temperature creep behaviour is introduced using the time hardening law. To study the problem several results are presented, as the effect of the material model on the plastic strain accumulation, the effect of the notch severity and the mesh element type and sensitivity. All the findings further confirm that the phenomenon observed is not an artefact but a real mechanism, which needs to be considered when assessing off-design condition. Moreover, it might be extremely dangerous if the cyclic loading condition occurs at such a high loading level.

A simple numerical model has been proposed for laser cladding. The model does not involve complex techniques such as cell addition, moving mesh, or prescribing a clad profile with a certain polynomial function. Instead, a mass function has been introduced to register the clad mass deposition on substrate, and from which the clad-track height can be estimated. The model takes several operational parameters, laser power, laser-head speed, and clad powder feeding rate, into consideration and predicts clad-track geometry, dilution, and substrate temperature. Experiments using two different combinations of substrate and clad powder materials to lay single and multiple clad tracks were conducted to provide data for model validation. The results show that the present model returns good agreement with experimental clad profiles for single and multiple tracks.

When the Symmetric Galerkin boundary element method (SGBEM) based on full-space elastostatic fundamental solutions is used to solve Neumann problems, the displacement solution cannot be uniquely determined because of the inevitable rigid-body-motion terms involved. Several methods that have been used to remove the non-uniqueness, including additional point support, eigen decomposition, regularization of a singular system and modified boundary integral equations, were introduced to amend SGBEM, and were verified to eliminate the rigid body motions in the solutions of full-space exterior Neumann problems. Because half-space problems are common in geotechnical engineering practice and they are usually Neumann problems, typical half-space problems were also analyzed using the amended SGBEM with a truncated free surface mesh. However, various levels of errors showed for all the methods of removing non-uniqueness investigated. Among them, the modified boundary integral equations based on the Fredholm’s theory is relatively preferable for its accurate results inside and near the loaded area, especially where the deformation varies significantly.

The influence of combined corrosion and vibration to the anti-loosening performance of a precision locknut used in a machine tool is investigated. Firstly, the locknut was submerged in 5% NaCl solution according to ASTM B895 standard for corrosion testing. The locknuts, after submerged in 1-hr, 2-hr and 4-hr periods, respectively, were then installed on the rotating spindle in a vertical dynamic impact tester for performing anti-loosening test. The initial installed pretension was 9800 N and the spindle was rotating in a constant speed of 1000 rpm. Turmogrease Li 802 EP lubricant was used on the contact surface between spindle thread and locknut. The set screws on the locknut were tightened sequentially and evenly in three-stage of torque: 1.96 N-m, 3.92 N-m and 5.88 N-m. Its real-time pretension variation with the periodic transverse impact and its final loosening torque were measured. Accordingly, the axial force ratio and anti-loosening torque ratio were calculated and discussed. It was found that corrosion treatment had similar influence on both the axial force ratio and the anti-loosening torque ratio. More corrosion on the locknut with longer submersion in NaCl solution deteriorated its anti-loosening characteristics. The result could serve as the reference for evaluating the fastening performance of precision locknut and guide the design and manufacturing for the application improvement.

In glaze ice conditions, beads on the surface usually grow to form roughness elements through coalescence, finally resulting in enhancement of local collection efficiency. However, the effects of roughness elements due to freezing of beads are not reflected on the local collection efficiency in CFD icing simulations. This is problematic for predicting the resultant ice shape, which may lead to inaccurate aerodynamic performance and load distribution. The aim of this study is to propose a macroscopic icing model which can reflect bead microscopic phenomena using the Eulerian approach. To this end, a correction was made for collection efficiency by introducing a novel parameter - the effective impinging angle- which is the angle to calculate the local collection efficiency depending on the physical state of surface. It is assumed that the parameter related to the contact angle represents the state of beads. The computational icing analysis of airfoil was performed using the proposed model both in the rime condition and glaze conditions. The results show that the icing characteristics in the feather region is captured with enhanced accuracy in both conditions.

This paper aims to investigate the freeze-thaw resistance of cement-paste containing with different diameter and content of multiwalled carbon nanotubes (MWCNTs) in terms of mechanical properties and microstructure. Three groups of cement-paste with MWCNTs diameter of 10-20 nm, 20-40 nm and 40-60 nm were prepared by incorporating 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt% MWCNTs by cement weight. Experimental results showed that the addition of 0.1 wt% MWCNTs with diameters of 10–20 nm effectively improved the freeze-thaw resistance of cement-paste. In addition, microstructural analysis of these cement-paste specimens showed that MWCNTs addition increased the materials’ initial porosity, but a proper amount of MWCNTs decreased the porosity of cement-paste after freeze-thaw cycles and effectively improved the pore size distribution. MWCNTs 10–20 nm in diameter were found to be the optimal size for improving the microstructure of these MWCNTs cement-paste

We formulate and solve the mathematical problem for antiplane cracks in a pre-stressed and pre-polarized piezoelectric material with static initial fields, assuming the initially deformed configuration of the body is locally stable. Using the boundary conditions of antiplane cracks, we get the Riemann-Hilbert problems. Nonhomogeneous linear complex differential equations having the unknown complex potential are obtained. For constant value of the applied incremental forces can be obtained the complex potentials, incremental displacement and stress fields corresponding to the third mode of the classical fracture. The problem of interaction of two collinear, unequal cracks in a pre-stressed and pre-polarized piezoelectric material, is also studied.

Specific conditions at the tip of a crack and discontinuities in a material are the challenges in analyzing the growth of cracks using conventional methods. In recent years, a method has been developed based on the non-local mechanics, called peridynamic theory, which has improved the analysis process of such structures. In this theory, the points of matter whose displacement or displacement derivatives are discontinuous are not distinguished from other material points. In this paper, we employed the bond-based peridynamic theory to investigate the rate of crack propagation and the path of crack growth in a beam with an initial crack due to low velocity impact. Two beams made of polymethyl-methacrylate (PMMA) and steel alloy with different projectile shapes were considered. The effects of changes in the impact velocity and the fracture toughness were studied and the obtained results were validated with other conducted studies. The crack path was predicted successfully and the branching of the crack was captured. The results confirm the ability of the peridynamic theory to model the crack growth in impact problems.