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A complementary methodology to the teaching of photovoltaic systems is proposed where students can develop a complete project if they were immersed in the industry. The complementary strategy incorporates activities usually not taught which are delivered via web-classroom to develop and reinforce the abilities needed to face the industry once they are graduated. A project-based learning strategy is used to reinforce the teaching on sizing, planning, modeling, installations with international standards, the start-up of a photovoltaic system with a monitoring system. Students carry out a financial investment analysis rarely taught, such as the calculation of the payback period, the internal rate of return and the net present value are made to ensure the project viability. Planning-dimensioning usually is taught analyzing the electrical bill to determine the required sizing capacity without considering the building installed capacity. A three-dimensional dimensioning using the geographic location of a possible installation is proposed to provide better information in terms of losses due to shading or obstacles that may affect an installation. Furthermore, it is proposed to perform an analysis of mechanical stresses on the mounting rail system under natural phenomena such as hurricanes. This type of analysis is not usually taught in classes and it is important since an investment can be lost due to natural phenomena as has already occurred in some solar plants. The proposed activities are aimed to develop self-directed learning skills motivating to do research leading to problem-solving and meaningful activities to work autonomously in a natural and real-life situation. This approach allows the teacher and students to ponder deeply about worthy subjects and issues. Five questions were formulated to verify student satisfaction; the 30 surveyed students have a very positive view of this complementary utilized strategy. [ABSTRACT FROM AUTHOR]

In this study, the stress analysis for an orthotropic thin film bonded to an orthotropic elastic substrate is addressed using both the analytical and finite element methods. The analytical method employs the integrodifferential formulation with the aid of membrane assumption. Utilizing the finite element method, the effect of orientation of the material principal directions are studied. The loading scenarios include a temperature gradient imposed on the film and a far-field uniaxial tension on the substrate. The results of current study indicate that the ratio of the film to the substrate stiffness plays a leading role in the film stress distribution. For the mechanical loading applied to the substrate, a soft thin film attached to a relatively stiffer substrate is preferred. The film can tolerate the induced thermal stresses as it is bonded to a softer host structure. The rotation angle of material orthotropy directions significantly affects the stress singularity near the film edges up to a certain extent. [ABSTRACT FROM AUTHOR]

Effective waste concrete recycling is desirable from the viewpoints of environmental protection and extending the working lives of waste concrete final disposal sites. Recycled fine aggregate powders (RFAP) were obtained by milling waste concrete, and in this paper, we attempted to use RFAP as reinforcement particles in a polyethylene (PE) composite material. The PE powder and RFAP were blended together, and composites were fabricated using compression molding. Our results showed that the flexural strength and flexural modulus of the created composites improved with increased RFAP content. The RFAP dispersion state was honeycomb-like in the composite material, and from inspecting the specimen side view after three-point bending tests, it was apparent that crack propagation proceeded into the RFAP part of the composite, between PE particles. We then performed elastic stress analysis on the composites, in order to define the RFAP reinforcing behavior, using finite element analysis based on the homogenization method. As a result, it was revealed that the Mises stress decreased with increased RFAP content, confirming that there is a potential role for RFAP as reinforcement particles in PE-based composites. [ABSTRACT FROM AUTHOR]

In this paper, the transverse loading of sandwich plate is formulated to study the three-dimensional stress field in the sandwich plates for various edge conditions. The formulation is based on the weak formulation approach. A complete three-dimensional displacement field is considered and the weak formulation approach is employed to obtain the governing equations of the plate using the three dimensional equilibrium equations of elasticity. An analytical solution is presented for governing equations when two opposite edges of plate are simply supported. A one-step stress recovery scheme is used to compute the out-of-plane stresses in the sandwich plates. A comparison is made with the predictions of exact elasticity solutions in the open literature and very good agreements are achieved. The distribution of stresses is investigated for various boundary conditions and the log-linear procedure is employed to study the order of stress singularity at free and clamped edge of the plate. It is seen that the present approach accurately predicts the distribution of out-of-plane stresses and local concentration of stresses in the vicinity of free and clamped edges of sandwich structures. [ABSTRACT FROM AUTHOR]

Topology optimization is a widely used lightweight design method for structural design of the collaborative robot. In this article, a topology optimization method for the robot lightweight design is proposed based on finite element analysis of the assembly so as to get the minimized weight and to avoid the stress analysis distortion phenomenon that compared the conventional topology optimization method by adding equivalent confining forces at the analyzed part's boundary. For this method, the stress and deformation of the robot's parts are calculated based on the finite element analysis of the assembly model. Then, the structure of the parts is redesigned with the goal of minimized mass and the constraint of maximum displacement of the robot's end by topology optimization. The proposed method has the advantages of a better lightweight effect compared with the conventional one, which is demonstrated by a simple two-linkage robot lightweight design. Finally, the method is applied on a 5 degree of freedom upper-limb exoskeleton robot for lightweight design. Results show that there is a 10.4% reduction of the mass compared with the conventional method. [ABSTRACT FROM AUTHOR]

The purpose of this paper is to present a study of creep deformation and stress analysis in a transversely material disk subjected to the rigid shaft by using Seth's transition theory. It has been observed that radial stress has the maximum value at the inner surface of the rotating disk made of isotropic material as compared to the hoop stress and this value of radial stress further increases with the increase in the value of angular speed. Strain rates have maximum values at the inner surface for the disk made of transversely material. [ABSTRACT FROM AUTHOR]

In drilling and completion operations, a packer is a downhole tool to seal the annular space between various sizes of string and borehole. As a key component of packer, slip plays a role of fixed support in the process of setting, thus ensuring a long-term stable sealing of the packer. Aiming at the problem of damage caused by casing pressure on the slip after setting, based on the stress analysis of slip during setting, the slip material with hardness lower than casing was selected, and its finite element analysis model was established. Then, the pressure-bearing law of the slip teeth under three tooth parameters was analyzed. The results of analysis were as follows. With the increase of the number of slips or the distance between teeth or tooth top angle, the strain of slips decreased, but the bending moment of slips increased. At the same time, orthogonal test method was used to optimize the parameters of the slips. The conclusion is that the tooth top angle is 90 degrees, the distance between teeth is 6 mm and the number of teeth is 16, which is the best combination of compressive effect. It will provide a reference for improving the long-term effectiveness of the packer seal in drilling and completion engineering. [ABSTRACT FROM AUTHOR]

Based on the "elastic modulus method" derived from the hypothesis of strain equivalence and test data of complete stress-strain curves of marble, granite, and sandstone under uniaxial compression, a damage model in the form of Logistic equation is proposed to simulate the stress-strain relation of rocks. This model can describe the complete deformation process of rocks under uniaxial compression satisfactorily. The used mathematical function is simple with just four model parameters, and each parameter has distinct physical meaning. The validity of the model is demonstrated by a mathematical deduction analysis and the model is further verified using laboratory test data. In addition, this model provides a method for estimating the elastic modulus of undamaged rocks using uniaxial compression test results and it presents a reasonable explanation of the chaos phenomenon occurred in uniaxial compression test. [ABSTRACT FROM AUTHOR]

The synergistic combination of mechanical fatigue stresses and environmental agents acting together can be more detrimental than that of the summation of the contributions of each mechanism acting separately. Major attempts to understand the contribution of the different agents (microstructure, chemical composition of environment, temperature, loading conditions, etc.) have been reported in the literature. Nevertheless, current knowledge is insufficient to address life estimation with a sound physical basis from the initiation of localised corrosion (such as pitting) to the estimation of crack propagation. Major simplifications and assumptions have been required in the development of life prediction methodologies. This paper reviews recent efforts made by the different interested parties, in both academia and industry, in the development of corrosion fatigue (CF) lifetime prediction procedures. The paper mainly focuses on the methodologies proposed in the literature for oil and gas, nuclear, energy generation and aerospace applications, dealing with pitting CF damage in aluminium alloys, carbon and stainless steels. The transition of a pit into a small crack (SC) and its growth is influenced by the interaction of the pit stress/strain concentration and the local environmental conditions, making the modelling of this stage of the utmost complexity. A major trend in the models reviewed in this paper is to simplify the analysis by assuming the pit (a volumetric defect) as a sharp crack, decouple the CF problem and account for the mechanical and environmental contributions separately. These procedures heavily rely on fitting experimental data and exhibit low generality in terms of application to varying system conditions. There is a clear opportunity in this field to develop mechanistically based methodologies, considering the inherent dependence of the damage mechanism on the interaction of environmental, metallurgical and mechanical features, allowing more realistic lifetime estimates and defect tolerance arguments, where pit-to-crack transition and SC initiation stages pose a significant challenge. Abbreviation: ASME: American Society of Mechanical Engineers; API: American Petroleum Institute; BP: British Petroleum; BS: British Standards; BWR: Boiling Water Reactor; CF: Corrosion fatigue; DNV: Det Norske Veritas; FCGR: Fatigue crack growth rate; FCI: Fatigue crack initiation; FCP: Fatigue crack propagation; FFS: Fitness for service; HA: Hydrogen assisted; HRR: Hutchinson, Rice and Rosengren stress fields; LC: Long crack; LEFM: Linear Elastic Fracture Mechanics; S-N: Stress vs. number of cycles [ABSTRACT FROM AUTHOR]

This article proposes a Rayleigh’s quotient–based damage detection algorithm. It aims at efficiently revealing nascent structural changes on a given structure with the capability to differentiate between an actual damage and a change in operational conditions. The first three damage detection levels are targeted: existence, location, and severity. The proposed algorithm is analytically developed from the dynamics theory and the virtual energy principle. Some computational techniques are proposed for carrying out computations, including discretization, integration, derivation, and suitable optimization methods. Field implementation strategies are also considered for the purpose of online damage monitoring. In order to prove the efficiency of this strategy, one experimental and three numerical case studies were conducted. The proposed algorithm successfully detected the damage in all simulated cases and estimated the damage severity with acceptable accuracy. The conclusion is that the proposed algorithm was able to efficiently detect damage appearance in a range of structures for various damage levels and locations, and under different operational conditions. [ABSTRACT FROM AUTHOR]

The strut-and-tie model has become an effective design methodology for deep beams replacing the conventional beam theory that does not apply to these members due to their geometric or static stress discontinuities. This article examines the applicability of shear models for deep beams with lightweight aggregate concrete. Eight lightweight aggregate concrete deep beams were constructed and tested to failure under concentrated loading. Tests were conducted to investigate the effects of shear span-to-effective depth ratio (a/d), ranging from 0.26 to 1.04, and an effective span–depth ratio (le/h), ranging from 2 to 3, on the failure mode and shear behavior of deep beams. All specimens presented a shear compression or shear-flexure failure mode. Failure from the flexure mode showed a dominant pattern with increasing a/d. The le/h value minimally influenced the diagonal cracking and ultimate strength of deep beams. In contrast, a/d significantly affected the beam strength. Our results were compared with predictions proposed by American Concrete Institute 318-14, Canadian Standard, EC2, the Tan and Cheng model, the softened strut-and-tie model, and the simplified softened strut-and-tie model, which are all based on the strut-and-tie model. These comparisons indicated that all of these shear methods can be used to predict the shear strength of lightweight aggregate concrete deep beams. [ABSTRACT FROM AUTHOR]

In the present work, for the first time, the accuracy of the Refined Zigzag Theory in reproducing the static bending response of sandwich beams is experimentally assessed. The theory is briefly reviewed and an analytical solution of the equilibrium equations is presented for the boundary and loading conditions under investigation (four-point bending). The experimental campaign is described, including the material characterization and the bending tests. The experimentally measured deflections and axial strains are compared with those provided by Refined Zigzag Theory and by the Timoshenko Beam Theory with an ad hoc shear correction factor. The Refined Zigzag Theory is shown to be more accurate than the Timoshenko Beam Theory, in particular for beams with higher face-to-core thickness and stiffness ratios and with a reduced slenderness. [ABSTRACT FROM AUTHOR]

A microscale model of multifilament reinforcement yarns made of technical carbon fibers is established based on the finite element method. The model is used to perform simulations of tensile failure. The failure behavior of dry multifilament carbon yarns is modeled using a maximum stress criterion with statistical distribution of the strength. The maximum stress is assigned to every single element and varied according to a normal distribution found in experimental tests of single filaments. The Weibull distribution is used for calculating the local failure stress. The material parameters are calculated in function of the element size to account for the volume-specific statistical breaking effect. Representative simulations of the tensile failure behavior prove the concept of the introduced assumptions. [ABSTRACT FROM AUTHOR]

On the basis of the introduction of the stiffness matrix of tensegrity structures, the eigenvalue analysis is carried out to study the influence of the prestress level on the stiffness of tensegrity structures. The triangular prismatic tensegrity structure, the star-shaped tensegrity structure and the star-shaped tensegrity structure with a central strut are selected as the numerical examples. The analytical results show that some eigenvalues increase linearly with the prestress level, whereas other eigenvalues firstly increase and then decrease or firstly decrease and then increase with the increase of the prestress level. This is because the stiffness matrix of the tensegrity structures is mainly composed of the material stiffness matrix and geometric stiffness matrix. As the contribution of these two parts of stiffness to eigenvalue models is different, the trends of eigenvalue variations are different with the increase of the prestressed level. [ABSTRACT FROM AUTHOR]

This work establishes a survival probability methodology for interface-initiated fatigue failures of monolithic ceramic crowns under simulated masticatory loading. A complete 3-dimensional (3D) finite element analysis model of a minimally reduced molar crown was developed using commercially available hardware and software. Estimates of material surface flaw distributions and fatigue parameters for 3 reinforced glass-ceramics (fluormica [FM], leucite [LR], and lithium disilicate [LD]) and a dense sintered yttrium-stabilized zirconia (YZ) were obtained from the literature and incorporated into the model. Utilizing the proposed fracture mechanics-based model, crown survival probability as a function of loading cycles was obtained from simulations performed on the 4 ceramic materials utilizing identical crown geometries and loading conditions. The weaker ceramic materials (FM and LR) resulted in lower survival rates than the more recently developed higher-strength ceramic materials (LD and YZ). The simulated 10-y survival rate of crowns fabricated from YZ was only slightly better than those fabricated from LD. In addition, 2 of the model crown systems (FM and LD) were expanded to determine regional-dependent failure probabilities. This analysis predicted that the LD-based crowns were more likely to fail from fractures initiating from margin areas, whereas the FM-based crowns showed a slightly higher probability of failure from fractures initiating from the occlusal table below the contact areas. These 2 predicted fracture initiation locations have some agreement with reported fractographic analyses of failed crowns. In this model, we considered the maximum tensile stress tangential to the interfacial surface, as opposed to the more universally reported maximum principal stress, because it more directly impacts crack propagation. While the accuracy of these predictions needs to be experimentally verified, the model can provide a fundamental understanding of the importance that pre-existing flaws at the intaglio surface have on fatigue failures. [ABSTRACT FROM AUTHOR]

This paper investigates the linear steady state problem of several moving cracks in a functionally graded magneto-electro-elastic strip subjected to anti-plane mechanical and in-plane electric and magnetic loading. For simplicity, it is assumed that the properties of the strip vary continuously according to exponential functions along the thickness of the functionally graded piezoelectric piezomagnetic (FGPP) layer. By combining the dislocation method and integral transform technique, an exact solution in closed form to this problem is obtained. Electro-magneto-mechanical loads are applied on the crack surfaces, which are assumed to be magneto-electrically impermeable. Numerical examples are presented to show the interesting mechanical and electromagnetic coupling phenomena induced by multi-crack interactions. Finally, the effects of crack velocity, material constants, and geometric parameters upon the field intensity factors are studied. The results are useful for the design of the magneto-electro-elastic structures. [ABSTRACT FROM AUTHOR]

By combining advanced imaging tools with morphology-based numerical modelling, a methodology has been proposed to measure the wood-adhesive bond performance at the micro level. Through this integration of multi-modal and multi-scale tools, this methodology provides a tool to understand the complex interactions between wood and adhesive phases at a microscale. Focusing all measurements and modelling on matched physical specimens avoided many simplifying assumptions. Direct measurement of strain development validated that the model was capable of representing the effects of cellular structure and adhesive penetration. With this measurement tool one can analyse stress and strain distribution patterns throughout adhesively bonded materials and virtually experiment with a range of variables like adhesive properties, wood species, compression levels, processing parameters, penetration patters, etc. [ABSTRACT FROM AUTHOR]

In this work, the authors discuss a systematic method of characterizing the damage process in graphene. The mathematical formulation is limited to the elastic range. In the elastic constitutive equation for graphene, both the second-order and third-order elastic stiffnesses are considered. The formulation is performed within the framework of Continuum Damage Mechanics. Thus, both the hypotheses of elastic strain equivalence and elastic energy equivalence are utilized. In addition to the classical damage variable that is defined in terms of the cross-sectional area, a new damage variable is introduced and defined in terms of the surface area. This particular damage variable is suited for general nanomaterials, especially graphene. Both the scalar and tensorial formulations are presented. The special case of plane stress in graphene is illustrated as an example using the derived general equations and some interesting results are obtained. [ABSTRACT FROM AUTHOR]

The fatigue behaviour of two-dimensional weave composites under constant and variable amplitude loading was discussed in this article. The theories of life prediction methods were represented, including cycle counting, S-N formulation, constant life diagrams (CLD), damage accumulation rule and stress analysis. Special focuses on CLDs were studied through the interpolation method known as the kriging model. Fatigue tests under constant amplitude loading were carried out utilising the servo-hydraulic Shimadzu testing machine. Tension-tension, tension-compression and compression-compression loading patterns were investigated in fatigue testing. The macro-failure mode was obviously different between tensile and compressive loading. Micro-failure surfaces were observed in micro-mechanism with scanning electron microscopy (SEM). The Basquin equation and the linear Palmgren-Miner (P-M) rule were employed to characterize the fatigue properties under random loading conditions. A new constitutive relation was introduced which took into account the tensile-compressive asymmetry of composites. Finally, the benchmarking for the stochastic loading case was executed using proposed methodology and variable amplitude fatigue experiments. Through the contrast between prediction and the experimental data, it was inferred that the proposed prediction method under any loading conditions (stress ratios and ranges) gave an accurate life prediction. [ABSTRACT FROM AUTHOR]

A thin rectangular plate is modelled as an (initially flat) shell. Following Koiter, the two fundamental forms of the deformed middle surface are then used to define the strain measures of the body. On the middle surface of the plate two local coordinates are introduced: we will call them longitudinal and transversal, respectively. It is assumed that the components of the displacement field which characterize the middle surface kinematics can be expressed as a product of two functions: one defined along the longitudinal coordinate and one defined along the transversal coordinate. Given an explicit expression of the latter functions, the 2D plate fields are reduced to 1D ones. The functions of the transversal coordinate are chosen so that the stretch along it together with the membrane shear vanish. It is worth noting that the linearization of these constraints leads to the well-known Vlasov’s assumptions. It is shown that by modelling each side of a thin walled beam as a 1D continuum, the entire assembly can be reduced to a 1D model as well. This procedure gives rise to an hyperelastic 1D beam model in which at least the warping effect is taken into account. The main features of the model are shown by means of some simple applications. [ABSTRACT FROM AUTHOR]

We consider an interface crack whose crack faces are coated with a thin reinforcing film of separate elastic material. We obtain asymptotic solutions, which, in the case of plane elasticity, demonstrate that the addition of the thin film effectively eliminates the well-known oscillatory behavior of the displacement and stress fields in the vicinity of the crack tip leading to a strong square-root stress singularity. In the case of anti-plane elasticity, the effect of the reinforcement is to reduce the order of the stress singularity at the crack tip. In addition, we demonstrate that the reinforcement induces a displacement field which is smooth locally and bounded at the crack tip. [ABSTRACT FROM AUTHOR]

Free vibration of a fiber-reinforced polymer honeycomb sandwich beam with sinusoidal core configuration is studied based on a refined sandwich beam theory. Using a micro/macromechanics approach for face laminates and a mechanics of material approach for honeycomb core, the equivalent elastic properties of face laminates and honeycomb core are obtained. A free vibration model based on the refined sandwich beam theory is formulated using the Hamilton's variational principle. Analytical solutions for a cantilevered sandwich beam are obtained by the Ritz method. Experimental results conducted on the fiber-reinforced polymer honeycomb sandwich beams with different lengths are applied to validate the proposed analytical solutions. As a comparison and further verification, the analytical solutions based on the Timoshenko beam theory and high-order beam theory are also presented. The analytical solutions in term of natural frequencies are compared with the numerical simulation results as well. Good agreements among various comparisons demonstrate the accuracy and capability of the refined sandwich beam theory and its potentials in design applications and health monitoring of fiber-reinforced polymer honeycomb sandwich beams. [ABSTRACT FROM AUTHOR]

Solid-state sintering theory predicts shrinkage kinetics assuming the two-sphere model. Spheres are of equal diameter, undeformed and smooth. The actual condition of powder particles in cold compacted green parts deviates very much from this model: particles have a broad size distribution and an irregular surface profile, they are not spherical and plastically deformed. Therefore the sintering stress cannot be directly correlated to the particle radius, as made in the two-sphere model. The actual neck curvature radius should be therefore determined. In this work, a first attempt to determine sintering stress experimentally is presented. Iron green parts produced by cold isostatic pressing were pre-sintered in order to provide a minimum consolidation avoiding densification. By means of image analysis, the microstructure was investigated to characterise the particle and the pore morphology, and in particular their profiles. A geometrical model of the pore morphology was proposed, from which the radii of curvature in correspondence of the neck regions may be calculated. [ABSTRACT FROM AUTHOR]

Competition of a crack and two debondings at the interface of a circular rigid inclusion in an infinite elastic body is analyzed under uniaxial loading in the x and y directions, respectively, and under biaxial uniform loading. It is investigated how these debondings develop along the interface of the inclusion from the initial debondings and where a crack occurs from the tip of debonding. Particularly, when there are both possibilities of the debonding development and of the crack occurrence from the tip of the debonding, it can be decided which phenomenon actually occurs. The angles at which the debondings develop and the crack occurs are determined. The magnitude of the load is also determined. As the criterion for debonding development and crack occurrence, strain energy release rates are used. Moreover, the restricting condition is that the normal stress at the interface ahead of the debonding tip is positive and the stress intensity factor of mode I just after crack occurrence is positive. As for the load, the constant load and the gradually increasing load from zero are considered. The stress analysis is carried out as a mixed boundary value problem with two stress and two displacement boundaries of plane elasticity. The rational mapping function of a sum of fractional expressions and complex stress functions are used for the stress analysis. [ABSTRACT FROM AUTHOR]

An increasing threat of global terrorism has led to concerns about bombings of buildings, which could cause minor to severe structural damage. After such an event, it is important to rapidly assess the damage to the building to ensure safe and efficient emergency response. Current methods of visual inspection and nondestructive testing are expensive, subjective, and time consuming for emergency responders' usage immediately after an attack. On the other hand, vibration-based damage detection methods with wireless smart sensors could provide rapid assessment of structural characteristics with low cost. For blast analysis, structural response is usually determined using a simplified SDOF version of the undamaged structure, such as used in a Pressure-Impulse (P-I) Diagram, or using more complex FEM (finite element method) models. However, the simplified models cannot take into account damage caused by blast focus at a specific location or on a specific element, which may induce local failure leading to potential progressive collapse, and the more complex FEM models take too long to derive applicable results to be effective for a rapid structural assessment. In this paper, a new method to incorporate vibration-based damage detection methods to calculate the multi degree of freedom structural stiffness for determining structural condition is provided to create a framework for the rapid structural condition assessment of buildings after a terrorist attack. The stiffness parameters are generated from the modal analysis of the measured vibration on the building, which are then used in a numerical simulation to determine its structural response from the blast. The calculated structural response is then compared to limit conditions that have been developed from ASCE blast design codes to determine the damage assessment. A laboratory-scale building frame has been employed to validate the developed use of experimentally determined stiffness by comparing the P-I diagram using the experimental stiffness with that from numerical models. The reasonable match between the P-I diagrams from the numerical models and the experiments shows the positive potential of the method. The framework and examples of how to develop a rapid condition assessment are presented. [ABSTRACT FROM AUTHOR]