Point Of Load Application Research Articles

Micromotion analysis of immediately loaded implants with Titanium and Cobalt-Chrome superstructures. 3D finite element analysis.

ObjectiveThe aim of this study was to evaluate the amount of micromotion of dental implants under immediate loading supported by Titanium (Ti) and Cobalt‐Chrome (Co‐Cr) superstructures.Material and methodsA model of tridimensional half‐edentulous maxilla with three dental implants was made using the Finite Element Analysis (FEA). Two standard and one zygomatic implants were connected to a superstructure with an elliptic section of 6x 3 mm (mm). Two study models were established. Model A: Titanium (Ti) alloy superstructure; Model B: Cobalt‐Chrome (Co‐Cr) alloy superstructure. To simulate an immediate‐loading situation, a friction coefficient of 0.71 was applied between the implant and the bone surface. An axial load of 252.04 [N] was applied on standard and zygomatic implants.ResultsThe Micromotion of dental implants was similar in both superstructure situations. The amount of micromotion was slightly higher in B1 and B3 models (Co‐Cr alloy‐superstructure) compared with A1 and A3 models (Titanium alloy superstructure). The micromotion values in two groups were greater than 150 μm in the incisive region (standard implant) and molar region (zygomatic). In general, the micromotion was higher on the implant that received the load with respect to the other implants. The greater difference was observed when the load was applied on the standard implant A1 (Model A1 = 189.12 μm) compared with standard implant B1(Model B1 = 263.25 μm).ConclusionsWithin the limits of present study, all implants on different load application points showed micromotion; in general, the amount of micromotion was slightly higher in the implants connected with Co‐Cr alloy superstructure.

Mechanotropism of single cells adhering to elastic substrates subject to exogenous forces

Adherent cells are able to actively generate internal forces, channelled by cytoskeletal protein filaments and transmitted through transmembrane receptors to the surrounding environment by means of focal adhesions. Cells also dynamically interact with extracellular matrix by sensing external chemo-mechanical stimuli and then inducing formation of stress fibres mediated by polymerization/de-polymerization processes which continuously redesign the interplay between structural organization and contractility activities in the cytoskeleton, so orchestrating selected signal pathways at the basis of many important cell’s physiological functions like adhesion, migration and division. Despite chemo- and duro-taxis have been intensively studied in the last years to understand how cells move on a substrate, their polarization and reorientation – observed during gastrulation, wound healing and morphogenesis – are only partially understood. By starting from the evidence highlighted in some recent studies that cells reorient in response to substrata deformation by essentially obeying a pure mechanical interaction, we propose to interpret the seeming overall cells’ rotation resulting from the reconfiguration of their cytoskeleton – here named mechanotropism – as a nonlinear optimization problem in which the adherent cell aims to align along directions leading it to minimize a physically coherent measure of work spent to deform the elastic substrate while retaining a prescribed level of homeostatic contractile force. To do this, the single-cell is simply modelled as a finite size contractile force dipole that acts on the boundary of a half-space perturbed by applied point loads. The effects of fences of forces acting orthogonally and tangentially on the boundary of the adhesion medium and encircling the cell are then investigated, so obtaining solutions that predict multiple non-trivial cell polarizations as functions of number, direction, relative magnitude and distance from the cell-dipole of the forces, as well as of the substrate’s Poisson ratio, with unprecedented outcomes under the hypothesis of auxetic (i.e. negative Poisson ratio) materials. The results lead to envisage that the proposed theoretical model might contribute to unveil the mechanobiological principles ruling in vivo cells orientation processes by guiding the design of novel experimental strategies and to conceive new mechanics-based markers for guessing cells’ pathological conditions from their mechanotropism.

Analysis of Additional Load and Fatigue Life of Preloaded Bolts in a Flange Joint Considering a Bolt Bending Load

The influence of the working load on the dynamic loading of the bolt was investigated in our study for two cases of flange joints. The analytical calculation according to the Verein Deutscher Ingenieure (VDI) 2230 recommendation and the numerical analysis using the finite element method (FEM) were performed for a model of a four-bolt joint. To verify the FEM analysis, the forces in the bolts were measured during preloading and during the application of the working load on the test rig. Based on the analytical and numerical results, the influence of the working load application point on the bolt load and its fatigue life was analysed for different cases. Comparison of the results shows that the analytical method overestimates the additional bolt stresses at low working load, mainly due to the extremely large fraction of bending stress. As the working load increases, the differences between the two methods decrease, but only for the reason that the analytical method can only linearly scale the overestimated results at lower working load, and FEM analysis, on the other hand, shows a progressive increase of the additional stress in the bolt at higher working loads due to the spreading of the flange. It is also shown that a high washer significantly increases the fatigue life of the bolt for two reasons: (i) a high washer reduces the additional stress in the bolt, and (ii) the high washer shifts the critical fatigue point from the thread area to the transition of the bolt shank to the head.

Flexural behavior of carbon-textile-reinforced concrete I-section beams

In the present work, the flexural behavior of carbon textile reinforced concrete (TRC) I-beams is investigated. Four-point bending tests were performed in I-beams, considering SBR-laminated textile and the following conditions: (a) plain cementitious matrix; (b) plain matrix and sand-coated textile; and (c) strain hardening cement-based composite (SHCC) matrix. The main goal of the research was to correlate the improvements on interface and matrix properties with the crack pattern, failure mode and ductility. For a comprehensive discussion, full mechanical characterization was performed and a design model is proposed for a better evaluation of the experimental results. Cracking behavior was greatly improved for conditions (b) and (c) with respect to (a), due to enhanced bonding between reinforcement and matrix in the former and due to fiber bridging mechanism in the latter. Beams with plain matrix exhibited brittle failure, whereas the beam having SHCC matrix showed premature local failure near load application point, resulting in an apparent ductility due to concrete softening mechanism. The reduced cracking load and the premature flange detachment along web-flange junction for condition (a) are also discussed. The proposed model is also validated through comparison with experimental results available in the literature.

Small signal modelling and stability analysis of internal ramp compensated constant on‐time controller with improved output voltage accuracy for point of load application

This paper investigates a constant on-time controller (COT) with internal ramp compensation and improved output voltage accuracy for point of load applications. The pulse width modulation (PWM) output is generated based on internal ramp: by sensing the regulated output voltage and comparing it to an internal reference target, an error signal is generated. This error signal is used to generate a reference for an added ramp signal, which is compared against an error voltage to generate a PWM trigger signal. An adaptive constant on-time scheme ensures a fairly constant switching frequency over a wide range of input and output voltages. This COT control algorithm is able to achieve high accuracy regulation (±0.5% of target) and fast transient response during load step change. A frequency domain small signal model is proposed, and an open loop gain transfer function is developed for this COT control system. The proposed small signal model and design analyses are verified with SIMPLIS simulations and experimental results.

Исследование прочности конструктивной противоледовой защиты винторулевого комплекса

Steering and propulsion are one of the most vulnerable elements of ice-going ships. This paper discusses structural ice protection for steering and propulsion units suggested and patented by the authors. This system protects rudder blade from the stern over its whole height. The paper gives the results of strength study for this structure depending on relative size of its elements, their stiffness ratios, as well as on application point and direction of ice load.

On development of a ring type mechanical force transducer: Shape optimization, modification and characterization with different optimization codes

This research paper focuses on the design and optimization of a ring type mechanical force transducer known as a proving ring. Three different optimization codes were used and compared to develop a universal ring design with optimum stress and enhanced ring sensitivity. In the optimization section, minimum ring thickness was found between 45 and 60° with maximum thickness at point of load application across all three optimization codes. Generalized reduced gradient code (GRG) yielded the largest decrease in maximum stress at 98% with a ring sensitivity increased by 19.5%. Bidirectional evolutionary structural optimization code (BESO) sees a slight reduction of stress at horizontal location at 8.3% but sensitivity was increased by 8%. ABAQUS shape optimization codes saw significant decrease in stress at horizontal location with reduction of 66.5% with ring sensitivity having the largest increase by 48.7%. From the optimization results, a simple geometric modification of the circular ring was made. Using finite element analysis, the modified ring design showed increased sensitivity as well as better stress levels compared to the conventional circular and octagonal ring shapes. With respect to the stress and deflection characteristics of the modified ring, the design can be said to be universal due to no minimal change in those factors when ring size increases. A last design modification was made to the modified ring by implementing a double ring design with two curved sections. It was found that the double ring design had lower stress levels compared to the modified ring with a slight increase in ring sensitivity.

Mode I debonding under large deformation conditions including notes on cleavage-peeling transition

Peeling and cleavage are common load cases for studying and evaluating adhesion between materials. The former is suitable for testing adhesion of thin or highly flexible materials for which the bending energy is negligible while the latter uses the rate of released bending energy as a measure of fracture energy. Their data reduction schemes are very different, which could lead to situations where peel-cleavage transition cases are misinterpreted. In this work, two analytical frameworks allowing transition between peel and cleavage configurations to be accounted for, are exploited. The first is an elliptic integral based solution, which in the present study is enhanced by the elastic foundation formulation to mimic interfacial reaction forces to external loading. The second is built on a pseudo-linear equivalent system, which allows representation of geometrically non-linear problem through a number of simple, linear segments. Both solutions are successfully confronted against each other and a geometrically non-linear finite element formulation. In addition to the analytical framework, a number of phenomenological insights into the transition are gained. These are presented as master curves relating geometrical and material parameters to the shape of the steady-state fracture response and the rotation of the load application point through the spectrum from cleavage to peeling. The disclosed results could prove valuable when designing, evaluating or analyzing mode I fracture of materials and structures of finite and non-zero bending stiffness.

Investigation of mechanical resistance of external thermal insulation composite systems (ETICS)

This paper investigates the mechanical resistance of ETICS, with different types of thin-layer rendering, by means of hard body and point load impacts on such surfaces. Core materials, made of different thicknesses of EPS (expanded polystyrene) were also tested for their resilience to such loads, as well as the elasticity of widely-used applied rendering. Test results focused on the possible impact level on ETICS in use. The robustness of the output results and testing methodology can be replicated and used independently by any stakeholder in the construction industry. The aim of the research is to develop a reliable method to determine the elasticity of the rendering which can be used to predict the mechanical resistance of ETICS. This paper presents the results of a study on the influence of a particular component of ETICS systems on their overall impact resistance, based on standards and modified methods. A novel simplified device for testing the rendering bending angle was designed, constructed and tested. The device investigates the rendering elasticity of ETICS. Results indicated that, with an increasing angle of cracking, the more elastic coats crack less while being subjected to an applied point load.

Revised Lewis Bending Stress Capacity Model

Background: During operation, cylindrical gearset experiences tangential, radial, and axial (helical gears only) force components that induce bending, compressive, and shear stresses at the root area of the gear tooth. Accurate estimation of the effective bending stress at the gear root is a challenge. Lewis was the first person who attempted estimating the root bending stress of spur gears with some reasonable accuracy. Various gear standards and codes in use today are modifications and improvements of the Lewis model. Objective: This research aims at revising the Lewis model by making adjustments for dynamic loads, shear stresses, axial bending stress for helical gears, and stress concentration factor that is independent on the moment arm of tangential or axial force component. Methods: An analytical approach is used in formulating a modified formula for the root bending stress in cylindrical gears starting with the original Lewis model. Intermediate expressions are developed in the process and works from many previous authors are reviewed and summarized. The new model developed is used to estimate the root bending stress in four example gearsets of 0o to 41.41o helix angle and the results are compared with those of AGMA (American Gear Manufacturers Association) formula. Results: Analysis from the examples shows that neglecting the radial compressive stress over-estimated the root bending stress by 5.27% on average. When shear stresses are ignored, the root bending stress is under-estimated by 7.49% on average. It is important, therefore, to account for both compressive and shear stresses in cylindrical gear root bending stress. When the root bending stress estimates from the revised Lewis model were compared with AGMA results, deviations in the range of -4.86% to 26.61% were observed. The stress estimates from the revised Lewis formulae were mostly higher than those of AGMA. Conclusion: The new root bending stress model uses stress concentration factors (normal and shear) that are independent of the point of load application on the gear tooth. This decoupling of stress concentration factor from the load moment arm distinguishes the new model from AGMA formula and brings bending stress analysis in gear design in line with classical bending stress analysis of straight and curved beams. The model can be used for both normal contact ratio and high contact ratio cylindrical gears.

Nonlinear analysis of laterally loaded rigid piles at the crest of clay slopes

This paper proposes a method for nonlinear analysis of a rigid pile under lateral load at the crest of clay slope. It is assumed that the ultimate soil resistance in front of the pile and behind the pile vary nonlinearly with depth. The modulus of horizontal subgrade reaction in front of the pile and behind the pile vary nonlinearly with the pile displacement at ground surface. The horizontal shear resistance at the pile base is considered and a bilinear relationship between the shear resistance and the displacement is used. Three distribution patterns of the soil resistance along a pile are also considered. Based on the force and moment equilibrium, the system equations are derived for a laterally loaded rigid pile in sloping ground with different soil resistance distribution patterns. The proposed method is validated by comparing its results with those from field tests, finite element analyses and a theoretical method. Finally, the method is used to analyze the effect of slope angle, pile-soil adhesion factor, height above ground surface of point of load application, pile diameter and embedded length on the lateral response of rigid piles.

Next Generation of Power Supplies—Design for Manufacturability

In today’s market, quality and reliability in power electronics products are a given. Greater emphases are placed on high efficiency, high power density, and low cost. Most products are custom-designed with significant nonrecurrent engineering and manufacturing processes that are labor-intensive. In certain isolated areas, we have witnessed improvements by integrating power devices, drivers, sensing, and control, in the forms of standard power modules, such as the “Intelligent Power Module” (IPM) in small motor drives and “Dr.MOS” in power supplies for point-of load applications. The major road blocks for widespread applications using these more integrated solutions hinge on the ability to integrate large and bulky passive components with power semiconductors in a form suitable for automation. Suffice it to say that the design practice for magnetic components has remained largely the same for the past five decades. With recent advances in wide-bandgap (WBG) power semiconductor devices, namely, SiC and GaN, we have witnessed significant improvements in efficiency and power density, compared with the current practice using silicon counterparts. Furthermore, with significant higher operating frequency, the integration of magnetic components with embedded windings in the PCB is feasible for a wide range of applications. Design trade-offs, previously considered neither practical nor conceivable, can be realized, not only with significant gain in efficiency and power density but also with drastic improvements of EMI/EMC and manufacturability. Several examples are given to illustrate the new design paradigm.

AN INVESTIGATION OF A GENERATIVE PARAMETRIC DESIGN APPROACH FOR A ROBUST SOLUTION DEVELOPMENT

AbstractThe main design activity in engineering practice is to adapt existing designs or to create variants of existing products to new demands, which require a robust model against both parametric and topological changes. To design such a kind of model becomes a big challenge, especially in the development of structural components due to the number of load application points, variable load cases and restrictions from manufacturing technologies. Thus, the generative parametric design approach is applied to generating high dynamic product models, allowing them to be adjusted for changes feasibly.

A New Finite-Element Approach to Contact Problems

The use of boundary and volume finite elements in contact problems permits determination of the influence function for bodies of any specific form, with elimination of the indeterminacy at the point of load application; and direct construction of the system of equations for determining the contact regions and the corresponding contact-stress distribution, without the need for complex transformations and without loss of physical significance. As an illustration, the proposed method is used to solve a contact problem.

Research of the calculation scheme for the brake lever transmission and construction of the load model for the brake pads of freight cars

In the article, the points of load application effecting the pads and other parts of the freight car three-element bogie during braking is considered theoretically using the example of the 2D diagram of the brake rigging. The special differences between the operating conditions of the first and second triangles of the car brake rigging and their effect on the wear of the pads when the train is moving without braking are described. The different operating conditions of the triangles are described to establish a causal relationship regarding the abnormal wear of the brake pads of the three-element bogies. For the first time, a calculation algorithm of a more accurate approach to theoretical calculations was proposed to determine the actual pressing forces in the brake pads on the wheels of the bogies. It proves the existence of the theoretical error, which is now inherent to the design models of freight cars brake rigging elements. The obtained algorithmic equations will help assess the wear of the brake pads and its effect on the stress-strain state in order to guarantee the railway traffic safety during the relevant theoretical and practical studies.

An improved stiffness matrix model of the functional spinal unit for application to an improved understanding of pathological changes

The stiffness matrix is a useful way to describe the mechanical behaviour of the functional spinal unit, which is defined as the superior and inferior vertebrae, capsules and ligaments. This usefulness is extended by means of the concept of the “balance point”. The balance point is the load application point where the coupling coefficients of the stiffness matrix are minimized. Theoretical considerations are used to demonstrate that the stiffness matrix varies with load point location and thus a single stiffness matrix does not fully characterize the motion segment as well as to derive the stiffness matrix at any one specified point from the stiffness matrix at some other specified point. Special characteristics of the stiffness matrix obtained by loading through the “balance point” were shown. Some possible advantages derived from mechanical testing using the “balance point” concept are discussed. This study validates an improved stiffness matrix model that enhances the understanding of pathological changes by setting the gold standard of the behaviour of a normal functional spinal unit.

A free, square, point-loaded ice sheet: A finite element-discrete element approach

Deflection of a free, thin, square, elastic, point-loaded ice sheet is studied. A three-dimensional, combined finite element-discrete element method (FEM-DEM) is applied. Examined is a set of square, self-similar (plan view) ice sheet samples with the side lengths of L=20, 40, 80, and 160 m; thicknesses of h=0.5, 1.0, and 1.5 m; and the average discrete element sizes of l=2h and 3h. The samples are generated and meshed via a centroidal Voronoi tessellation procedure. Each mesh is unstructured and consists of convex polyhedra as the discrete elements and a Delaunay-triangulated, in-plane beam lattice of co-rotational, viscously damped Timoshenko beam finite elements. Two load cases are considered: a sheet sample subjected to i) a vertical, centrally applied point load; and ii) a vertical point load on an edge. In both load cases, a good agreement is found between the deflections computed with the FEM-DEM approach and with FEM. Maximum, non-dimensionalized deflections w¯max (w¯max=q/Fz, where q=q(wmax) is an approximate, resultant reaction force due to the buoyancy, wmax the computed maximum deflection, and Fz the applied point load) scale, in each load case, either by a power-law, w¯max∝hm1(L), or exponentially, w¯max∝10m2(h)L, depending on whether computed over h (for each L) or vice versa. The exponents m1 and m2 are not constants, but functions of L and h, respectively, and approximately equal in either load case. In-plane size estimates are sought for an FEM-DEM sheet sample to represent either a) an infinite, elastic, point-loaded ice sheet; or b) a semi-infinite, elastic, point-loaded (with the load on the free edge) ice sheet with a free edge. A free, square, point-loaded FEM-DEM sheet sample well approximates both a) and b), if L/2>≈5lch, where lch denotes a characteristic length.

Loading points for industrial scale sandwich structures – A numerical and experimental design study

Objective of the present study is a design study on optimum geometries for load application points for thermoplastic sandwich structures suitable for industrial scale mass production. The design of the loading points is performed using a combined numerical and experimental multi-step approch. In a preliminary numerical study, promising design options are identified using a four-step procedure: starting from an initial concept phase, a trade-off analysis of a variety of design options is performed. Based on the results, the three most promising options are optimized further until a detailed optimization of the leading design option is performed. All design options are chosen such that they can be manufactured in an economic manner using a compression molding process for functionalization of sandwich structures with thermoplastic tape laminates as their face sheets. In a subsequent experimental study, the three most promising options identified in the preliminary numerical design study are re-designed considering manufacturing aspects, manufactured, tested and assessed under quasi-static, creep and fatigue conditions.

Analysis, Design, and Control of Switching Capacitor Based Buck–Boost Converter

A switching-capacitor-based buck–boost converter (with common ground) for point of load applications is proposed in this paper. It is capable of operating in stand-alone buck or boost mode in addition to its primary operation of performing the buck–boost conversion. The striking feature of the proposed converter is low source current ripple content irrespective of its mode of operation (buck–boost, buck, or boost). First, feasible pulsewidth modulation schemes for the proposed converter are identified and thereafter the corresponding circuit performance analysis, steady-state analysis, and state-space modelling is established. Through steady-state analysis, voltage gain expressions are formulated and equations defining L - C components are derived in terms of their ripple quantities. The state-space models are used to formulate small-signal analysis and to obtain the relevant transfer functions required in the controller design. A voltage-mode/current-mode controller is designed, with a tradeoff in bandwidth, to control the proposed converter and transit it from buck to boost mode or vice versa seamlessly. A 30–55 W , 100 kHz, prototype point of load converter with 36-V input dc source is built to supply power at constant load voltage of either 48 or 28 V. The proposed converters’ effectiveness is demonstrated experimentally in terms of reduced source current ripple along with seamless transition from buck to boost mode and vice versa.

Numerical and experimental analysis of bonded joints with combined loading

The metallic materials bonding using structural adhesives has become an increasingly used process, presenting advantages when compared to other fastening methods such as screws and rivets. The aim of this paper is the numerical evaluation of bonded joints with combined loading (traction and shear) using the finite element method, comparing the results obtained with the experiments performed at the same configurations. Considering adhesive joints with the same bonded area, but with different linear dimensions, the mechanical strength may be different, which characterizes the shape factor. In this way, the analyzes considered the bonded area shape factor in nine different configurations, being modified both the height and the width of the joint, considering two points of force application for each group. For the numerical simulation, the cohesive zone models (CZM) were used, which use the concepts of linear elastic fracture mechanics (LEFM). These models consider that one or multiple interfaces or regions of fracture may be artificially introduced into the structures, which is done through the separation-traction laws. For this purpose, DCB (double cantilever beam) and ENF (end notched flexure) tests were performed, measuring this way the essential cohesive properties to the numerical modeling, especially the critical energy release in I and II modes (normal and shear, respectively). The influence of some cohesive properties on the maximum load of the bonded joint was investigated. The good numerical and experimental concordance in different configurations studied confirms that the CZM provide consistent results with the bonded joint experiments for the presented conditions of adhesive thickness, surface treatment and load application point, not only in single lap joints, but also in combined loading joints, whose investigation was done in this work.