Mechanics of Materials and Structures

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Computational models for impact mechanics and related protective materials and structures

Computational models for impact mechanics and related protective materials and structures

The proposed analytical models [157] to describe the mechanics of these modified honeycombs are based on geometrical consideration and on the elastic theory of plates and shells and, thus, are limited to the description of the elastic regime up to yielding onset. The high complexity of phenomena within the material, which experiences yielding, elastic-plastic instabilities, and fracture under large strain, in addition to the geometrical non-linearity introduced by the complex 3D geometry, require the use of non-linear simulation in order to thoroughly describe mechanical behaviour of such honeycombs up to crushing. Further advantages are associated with the virtual modelling. The closed cell structure of the honeycombs does not allow to directly visualize the formation and the evolution of plastic folds and fractures during the experiments. Moreover simulations can go beyond the mere measurement of the force displacement curves being able to measure other important quantities such as local stresses and strain (and thus highlight with precision the yielded and damaged regions), to visualize the formation of shear bands, and to precisely control and evaluate the role of different frictional properties (static and dynamic coefficient of friction) at the contact interfaces on the overall behaviour. Scope of the study was the development of a simulation model able to predict the energy absorption capability of such structures and to be use for future studies on further geometries or constituent materials.

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Application of Damage Mechanics for Prediction of Failure of Structural Materials and Elements

Application of Damage Mechanics for Prediction of Failure of Structural Materials and Elements

Very interesting research with an extremely practical application was done by Wen and Mahmoud [24]. Authors attempted to model numerically steel joints in building structures. The problem concerned phenomenon of block shear failure in bolted steel connections. Due to high complexity, i.e. the varying stress-state conditions along the failure path, the applied damage model required to take into account all components of stress-state prevealing in the failure region. For this type of joints the ductile fracture is observed, especially on the shear plane. This failure mechanism is dependent on stress triaxiality and on Lode angle parameters. Basing on this assumptions, the numerical simulations of block shear in gusset plate and coped beam connections were conducted. By using newly developed ductile fracture criterion, taking into consideration the stress triaxiality and Lode angle parameter it was possible to model and analyse total failure material and elements.

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Mechanics of Micro-Structured Soft Materials and Their Applications in Adhesion and Wetting

Mechanics of Micro-Structured Soft Materials and Their Applications in Adhesion and Wetting

In our study, we changed the geometry to stabilize the pillar recovery for wettability manipulation and patterning, as shown in Chapter 4. We demonstrated that the static contact angle and the sliding angle can be controlled simply by deforming and recovering the SMP pillar arrays. At the same time, anisotropic droplet shape was observed for large spacing patterns. In this aspect, it is interesting to investigate how the orientation of deformation, which is always fixed to the lattice vector direction in our study, would impact the shape of the droplet. Especially, we mentioned that for smaller spacing patterns, saw-tooth exists as the pillar overlaps where the droplets atop are circular in shape. Conversely, if the SMP pillars are deformed along the diagonal or other orientation, where the spacing along the chosen direction is larger than the pillar height, the deformed pillars should also form channel-like structures, inducing the formation of anisotropic droplet. Varying the deformation direction can thus control the morphology of the droplet. On the other hand, the anisotropic liquid spreading behavior on metal- tilted SMP pillars deserves a systematic study, exploring the spreading speed, droplet retention force and spreading dynamics as a function of tilting angle and comparing to existing systems. 7, 8 Lastly, while the hierarchical structures were fabricated by selective picking up of silica nanoparticles onto the SMP, there are a variety of particles of different size, 9, 10 type 9, 11, 12 and shape 12 can be used, which could lead to novel wetting and optical properties.

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Mechanics of Viscoelastic Thin Walled Structures

Mechanics of Viscoelastic Thin Walled Structures

In the proposed modeling framework, the composite has been assumed to be thermorheologically simple and its temperature dependent behavior is the same as that of the matrix. This assumption is generally not true for heterogeneous materials made of phases with distinct molecular structures. Perfect interfacial bonding has been assumed in the unit cell finite element modeling. It has been suggested that a thin interfacial region having mechanical properties different from the constituents exists because the molecular structures are altered when two constituents adhere. As good agreement has been obtained between model predictions and experimental results, it is concluded that in the present case this microscopic interfacial bonding effect is secondary. The micromechanical model presented is limited to linear viscoelastic behavior only. Since the difference in modulus between carbon fibers and epoxy matrix is generally more than 10 times, locally nonlinear deformation in the interfacial regions is possible when the composite is subject to larger overall deformation. The model predictions based on the assumption of linearity would produce an over-estimation of composite modulus.

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The implementation of building information 
		modeling technologies in the training of bachelors and masters at 
		Saint Petersburg Mining University

The implementation of building information modeling technologies in the training of bachelors and masters at Saint Petersburg Mining University

When studying special disciplines, such as Theoretical mechanics, Materials resistance, Basements and foundations, Reinforced concrete and stone structures, Metal structures, and others, students get acquainted with the software and computer complex Autodesk Robot Structural Analysis Professional and other finite-element programs (Ing+, Sofistik, Plaxis) (Demenkov, Trushko and Potseshkovskaya 2018; Demenkov, Goldobina and Trushko 2018; Protosenya, Karasev and Ockurov 2017; Sych 2012), which can be used to perform calculations of various building structures, buildings, and structures. It is known that Autodesk Robot Structural Analysis Professional allows performing accurate calculations of the most complex building structures and buildings in general by means of automatic meshing of finite elements, nonlinear algorithms, and an extensive library of calculation norms. Autodesk Robot Structural Analysis Professional easily connects with other Autodesk solutions, supporting two-way 3D communication with them.

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Determination of Fracture Parameters of High Performance Concrete

Determination of Fracture Parameters of High Performance Concrete

Cracking is an essential feature of the behavior of concrete structures. Even under service loads, concrete structures are normally full of cracks. Clearly, cracking should be taken into account in predicting ultimate load capacity as well as behavior in service. Fracture researchers have at the present no doubt that the introduction of fracture mechanics into the design criteria for all brittle failures of reinforced concrete structures (such as diagonal shear, punching shear, torsion or pull out, or for concrete dams), can bring about significant benefits. It will make it possible to achieve more uniform safety margins, especially for structures of different sizes. This, in turn, will improve economy as well as structural reliability. It will make it possible to introduce new designs and utilize new concrete materials. Fracture mechanics will be particularly important for high strength concrete structures, fiber- reinforced concrete structures, concrete structures of unusually large sizes, and for prestressed structures. The application of fracture mechanics is most urgent for structures such as concrete dams and nuclear reactor vessels or containments, for which the safety concerns are particularly high and the consequences of a potential disaster enormous.Facture mechanics is concerned with the qualitative description of the mechanical state of a deformable body containing a crack or cracks with a view toward characterizing and measuring the resistance of materials to crack growth . It is a relatively new area of solid mechanics research, with its foundation laid in the late 20 th century. Already it has broad application in systems ranging in size from micrometer length scales ( thin films) up to kilometer length scales ( earthquake fault lines). Fracture mechanics deals with the mechanical responses of a flawed or a cracked body subjected to the application of forces or stresses. For certain cracked configurations subject to external forces, it is possible to derive closed- form expressions for the stresses in the body, assuming isotropic linear elastic material behavior.Fracture behavior can be classified into three basic types (Fig 4.1), each associated with a local mode of deformation. Mode I, or the opening mode, where the principal load is applied normal to the crack plane, tends to open the crack. Mode II, or sliding mode, corresponds to in-plane shear loading and tends to slide one crack face with respect to the other. Mode III, or the tearing mode, refers to out-of-plane shear. A cracked body can be loaded in any one of these modes, or a combination of two or three modes.

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Mechanics of diffusion-induced fractures in lithium-ion battery materials

Mechanics of diffusion-induced fractures in lithium-ion battery materials

crack closure technique (VCCT) with the ANSYS finite element software (ANSYS, Inc. Canonsburg, Pennsylvania) is utilized to obtain energy release rates and the stress intensity factors [20]. Energy release rates are used to predict the fracture tendency and the stress intensity factors are used to relate stress fields around crack tips. The fracture mechanics information (energy release rates and stress intensity factors) are calculated from the command-coding interface of ANSYS [21], and they are currently not available on the graphical user interface of ANSYS.

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Experimental Analysis of Fracture and Damage Mechanics of Pre-Stressed Concrete Sleepers B70: Part B- Analysis

Experimental Analysis of Fracture and Damage Mechanics of Pre-Stressed Concrete Sleepers B70: Part B- Analysis

studied longitudinal crack propagation in pre-stressed concrete sleepers. In their experimental and numerical studies, the effects of extra pressure in rawlplug positions were modeled by applying cylindrical pressure inside the holes [Rezaie, Shiri and Farnam, 2012]. Fracture and damage mechanics of pre-stressed concrete sleepers B70 were analyzed experimentally. González-Nicieza and co-authors investigated the failure analysis of a railway track used for transporting heavy haul industrial freight [González-Nicieza et al, 2008]. Three dimensional finite element methods and a series of experimental programs are used to examine the failure mechanism of concrete railway sleepers by Goangseup Zi and colleagues [Goangseup Zi et al. 2012]. Also, in 2014, fatigue and failure of Pre-stressed concrete sleepers (or railroad ties) were investigated using full- scale experimental tests [Remennikov and Kaewuruen, 2014].

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Understanding cracked materials: is Linear Elastic Fracture Mechanics obsolete?

Understanding cracked materials: is Linear Elastic Fracture Mechanics obsolete?

Linear Elastic Fracture Mechanics has enabled the research community to solve a wide variety of problems of practical and scientific interest; however, it has historically suffered from two main shortcomings. Firstly, it predicts physically unrealistic singular stresses and strains at crack tips. Secondly, microstructural effects are lacking, so that a major source of size-dependent behaviour is not captured. Gradient-enriched elasticity overcomes both these shortcomings: singularities are avoided, so that crack-tip stresses can be used to assess integrity, and the inclusion of microstructural terms implies that size effects can be captured. In this investigation, it is shown that gradient-enriched crack tip stresses can directly be used to model the transition from the short to the long crack regime. The accuracy of this approach was validated by a wide range of experimental results taken from the literature and generated under both static and high-cycle fatigue loading. This high level of accuracy was achieved without having to resort to phenomenological model parameters: the extra constitutive coefficient was simply the (average) grain size of the material.

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Single-nary Philosophy for Non-Linear Study of Mechanics of Materials

Single-nary Philosophy for Non-Linear Study of Mechanics of Materials

In other approach, a Chinese philosopher named Trang Chau in 369-298 B. C., had a belief which contradicted the true - false view of the world. He stated that true and false are one and undivided – a single-nary philosophy. He advised that we should go out beyond the framework of binary thinking: true - false, black - white etc. in order to better understand the nature of things. By single-nary thinking, which will be represented in this work, we introduce a modification of Aristotle’s philosophy using modal logic and multi-valued logic (these logics we call ‘high-order’ logic). Next, non-linear cause - effect relations are expressed through non-additive measures and multiple-information aggregation principles based on fuzzy integration. In this study, non-linearity will be singled out as an important concept for understanding high-order complex systems. The study of real time behaviors required experiences and intuition, will be realized using truth measures (non-additive measures) and a procedure for information processing in intelligence levels. Here, emphasis is put on a multidisciplinary approach using a single-nary philosophy based on high-order logic (modal logic and multi-valued logic) and fuzzy arithmetic. Non-linear study of mechanics of materials, in this paper, is formulated as a problem of meta- intelligent system analysis.

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Evaluation of the Compatibility of Repair Materials for Concrete Structures

Evaluation of the Compatibility of Repair Materials for Concrete Structures

The repair was prepared by wrapping half of the horizontal repair plane with tape to prevent the repair material from leaking out and causing voids. The repair materials were applied by pouring the mix in the dam created by the tape and attach each block section into place. The blocks were pressed firmly into the repair material. Excess amounts of material were not allowed to drain so as to reduce the amount of voids. If the blocks were higher than the middle compressive zone of the concrete beam, it would not affect the overall strength of the beam since the strength is limited by the smallest moment arm in the pure flexural zone of the loading arrangement. As each block was placed into posi- tion, the vertical face mating with the beam or another block was coated with repair material and pressed together. Once all blocks were in place, the vertical crack was sealed with tape and the repair mix was poured over the crack to com- pletely fill all the voids. Once the two beams were repaired, they were allowed to cure for a minimum of 7 days before the tape was removed. The cracks were inspected for pres- ence of voids and no voids were observed.

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Efficiency and durability of wearable smart materials and structures

Efficiency and durability of wearable smart materials and structures

Moreover, while ceramics have a higher piezoelectric constant, the polymers are more flexible making them more appropriate for areas such as wearable applications (Vatansever et al., 2012b). Wearable applications, smart textiles, and e-textiles in general (multifunctional textile products) place specific limitations regarding the rigidity, elasticity, thickness, wearability, comfort etc. of the usually fibrous materials to be incorporated in the product, hence the need for piezoelectric material forms that emulate classic textile structures (fibres, yarns, fabrics). Multifunctional textile materials become increasingly important for combined applications. Piezoelectric fibres and yarns open a new field in the multifunctional textile area, especially for energy harvesting applications. It is expected that soon a garment using piezoelectric fibres will be developed capable of producing usable electrical power (Jost et al., 2014).

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Study on Flexoelectric Materials, Structures, and Its Applications.

Study on Flexoelectric Materials, Structures, and Its Applications.

Flexoelectricity has been mostly reported for insulating ferroelectric materials such as BaTiO3, SrTiO3, BST, BT-8BST, SrTiO3, PMN-PT and polyvinylidene fluoride (PVDF).[11]– [13], [18], [22], [52], [71], [80], [89], [90] However, recently, it was found that some semiconducting materials can also yield polarization upon strain gradients, like the oxygen depleted BaTiO3 (BTO-δ), whose flexoelectric coefficient can reach up to 1 mC/m.[52] In Section 1.3.4, we discussed this research with Error! Reference source not found.. Due to the o xygen depletion process, BaTiO3 (BTO) became an n-type semiconductor where the surface was fully oxidized and capped by the thin insulating layer. The enhanced flexoelectricity was induced by the surface reduced layer, where the strong electric field was generated in the semiconducting BTO-δ under strain gradients.

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Finite Element Modeling of CARBON nanoTUBES

Finite Element Modeling of CARBON nanoTUBES

Evaluation of the effective mechanical properties of single walled carbon nanotubes using a spring based finite element approach, Computational Materials Science, 41, 561-569 (2008). [9] B. WenXing, Z. ChangChun, and C. WanZhao, Simulation of Young's modulus of single-walled carbon nanotubes by molecular dynamics, Physica B: Condensed Matter, 352, 156- 163 (2004).

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EXPERIMENTAL TECHNIQUE TO EVALUATE THE NANOMECHANICS AT NANOSCALE OF CARBON NANO TUBES

EXPERIMENTAL TECHNIQUE TO EVALUATE THE NANOMECHANICS AT NANOSCALE OF CARBON NANO TUBES

quantum dots or synthetic chromophores to selected molecules .Although wide benefits emerge from the nanotechnologies, we have also to keep in mind that the toxicology of many nanomaterials has not yet been fully evaluated. Thus, while nanotechnology promises many solutions related to health care or energy saving based for example on low weight high strength materials, it remains important to develop at the same time the knowledge of their impact on our environment and for this, it is important to characterize as accurately as possible each nanomaterial.

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Application of Smart Materials in Smart Structures

Application of Smart Materials in Smart Structures

Smart building is one which monitors itself or that monitors itself and its environment in order to respond to changes in its condition. In large civil engineering structures such as bridges, an integrated instrument system could tell both maintenance in charge or the user of the structure, an enormous amount about both the environmental and traffic loading conditions and the general conditions of the bridge , when and whether it will be in need of structures.

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Micro mechanics modelling of smart materials

Micro mechanics modelling of smart materials

made composite materials, at over 6000 years old, in which a woven lattice of wooden strips called wattle is daubed with a sticky material usually made of some combination of wet soil, clay, sand, animal dung and straw. Many historic buildings include wattle and daub construction, and the technique is again becoming popular in more developed areas as a low-impact sustainable building technique [25]. Concrete is also a composite material, composed of aggregate (a broad category of coarse particulate material used in construction, including sand, gravel, crushed stone, slag and recycled concrete) bonded together with a fluid cement which hardens over time. Concrete can be formulated with high compressive strength, but always has lower tensile strength. For this reason it is usually reinforced with materials that are strong in tension (often steel). Concrete is used more than any other man-made material in the world. As of 2014, about 4.18 billion metric tons concrete was made [26].

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Aluminum and Composite Materials for Satellite Structures - A Comparison of Thermal Performance

Aluminum and Composite Materials for Satellite Structures - A Comparison of Thermal Performance

The satellite thermal control maintains temperatures of all satellite components within their allowable operational temperature limits, throughout the satellite mission. Aluminum and composite materials are used for satellite structures. Thermal control performance, structural properties and manufacturing cost are important factors in selection of satellite structures. In this paper, we present the comparison of thermal performance of aluminum and composites, used as structural materials for a small satellite. We have also studied the effect of thermal contact resistance, between the satellite main components and the structural elements, on the overall thermal performance of these satellite structures. The temperature results, for major satellite components in the two types of structures considered in this paper, show the improvement in the overall thermal performance of composite satellite structures over the aluminum satellite structure.

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Modern Insulating Materials and Flat Evacuated Structures

Modern Insulating Materials and Flat Evacuated Structures

There is complete analogy between heat flow in solids and electric current in metals. Models for solid conductance, based on simple constriction re­ sistance theory and prolonged heat paths, give quite realistic agreement with measured values especially for powder or fiber materials. Unfortunately, they are compressed substantially under atmospheric pres­ sure in many cases which means increase of conduc­ tivity. A major part of heat transfer reduction in pow­ ders can be explained by a simple model of Hertz contacts between smooth elastic spheres (with dif­ ferent radii r, moduli of elasticity E and Poisson num­ bers p). During the action of force F, real contact is formed over relatively small round area with radius rc , named Hertz radius, calculated from:

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Modeling and Analysis of Outrigger Reaction Forces of Hydraulic Mobile Crane (TECHNICAL NOTE)

Modeling and Analysis of Outrigger Reaction Forces of Hydraulic Mobile Crane (TECHNICAL NOTE)

The routes of the solution to this problem are listed as follows: first, the forces of each part are moved to the barycentre of this lifting system to get the total equivalent equilibrium gravitational force and total equivalent equilibrium moment; second, the reaction force of each outrigger is obtained via force and moment equilibrium equation sets of theoretical mechanics, and the deformation equations of each outrigger are extracted besed on Hooke’s law, when the boom rotates to different positions in horizontal direction as the lifting angle is restricted to the rotation radius in steady operation; third, as this problem is concerned statically indeterminate, thus, a compatibility equation of the deformation about one of the four outriggers is derived to solve the target forces.

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