Compressive Normal Force Research Articles

Poynting effect in fluid-saturated poroelastic soft materials in torsion

This work studies the Poynting effect in fluid-saturated poroelastic soft materials in torsion. The Poynting effect is a nonlinear mechanical phenomenon commonly observed in soft solids such as biological soft tissues, gels and rubber. When sheared or twisted, such materials tend to either expand or contract in the direction perpendicular to the plane of shearing or twisting. Thus, to maintain a constant height, a compressive (positive Poynting effect) or tensile (negative Poynting effect) normal force must be applied to the material’s sheared face or twisted end. The mechanical response of fluid-saturated poroelastic soft materials can be described using mixture theory. Although both of its constituents are intrinsically incompressible, the biphasic material as a whole is compressible since it may gain or lose fluid through its pores. Our model—an extension of the single-constituent, incompressible solid models found in anterior studies—allows one to quantify the effect of the fluid and the solid on the normal force and torque required to maintain the torsion deformation and shows that the anomalous negative Poynting effect cannot be attributed to the poroelastic nature of the material alone. We use finite element simulations to predict the normal force and torque for biphasic materials with weakly-compressible and fully-compressible Mooney–Rivlin skeletons and Holmes–Mow-type hydraulic permeability. We also approximate analytical expressions for the normal force and torque for a weakly-compressible Mooney–Rivlin solid, which set a benchmark for the numerical simulations.

A granular physics-based model for sediment dispersion

Current models of dispersion in marine sediments include losses due to fluid viscosity and shearing at grain-grain contacts. An additional loss mechanism, which is well established in granular physics but is not included in existing models, is the inelasticity of normal compression at grain-grain contacts. Additionally, force-bearing contact networks, often called “force chains,” involve primarily normal compressive forces. These “force chains” are known to play a dominant role in force transmission in granular materials, including wave propagation. Using theoretical analysis of a 1D model “force chain” as well as DEM simulations in higher spatial dimension, we show that this granular mechanics perspective, where forces are transmitted along lossy force chains, may be able to explain salient features of the acoustic properties of marine sediments. In particular, the low and high-frequency behavior of the attenuation coefficient match a large collection of experimental data. [This was supported by the Office of Naval Research.]

The Anatomy of an Innovation- Ziptek for Tissue Repair

All of the existing devices are load-sharing and stress shielded. If you have a tissue repair system that never releases the pressure on that tissue, then the tissue never experiences normal stress, i.e., compressive, tensile and sheer forces that are needed to create a normal tendon or ligament through remodeling. Our system, which is revolutionary not evolutionary, works such that the loop suture technology is not utilized. Resorbable button tissue repair technology is a technology whose biomechanics is completely different than suture loop technology.

Numerical investigations on infilled frames and predictive formulae in the elastic regime

An in-plane finite element model of infilled frame systems is formulated. A frame–infill interface capable of transferring only normal compressive contact forces is defined. The complex phenomenology affecting these systems is explored, with a focus on the contact/separation conditions at the interface. Comparisons with previously reported experimental and numerical findings are made, and the model is validated. Parametric analyses are performed. Interpolation formulae are determined, which estimate frame–infill contact lengths and global stiffness in the elastic regime.

Characteristics of force transmission in cohesive agglomerates impacting a rigid surface

We numerically analyze the characteristics of force transmission in a single wet particle agglomerate composed of spherical particles impacting a flat surface for a broad range of values of the cohesive force induced by the binding liquid and the initial falling speed of agglomerate by using an extensive discrete element method. The numerical method considers the spherical particles as rigid grains with the inclusion of the reversible capillary bonds between primary particles, each capillary bond induces the normal capillary attraction force and the normal viscous force. In this impact test, the force transmission characterized by the probability density function of the normal forces (tensile and compressive components) and the frictional forces which control the behavior of the early-stage impact and the early-stage deposition that observed from the mechanical responses of such agglomerate. We show that the force distribution strongly depends on the cohesive force and the impact velocity at the early-stage impact, whereas it is nearly independent at the early-stage deposition of agglomerate. In early-stage impact, in particular, the width of the positive and negative ranges of normal forces is inversely proportional to the cohesive force, the density of the normal compressive forces and tangential forces is inversely proportional to the cohesive force, whereas this density increases with increasing the impact velocity. Remarkably, by continue normalizing the normal and tangential forces by a speed ratio, defined as a ratio of the impact speed obtained at its first touching with the flat and gravitational particle velocity, all the probability density functions of normal and tangential forces collapsed on a single curve.

Pressure distribution on rolling-slide contact problem

AbstractIn this paper the generalized model of contact of two plan bodies that roll and slide or just roll is presented. The analytical solution of the correct distribution of pressure in the contact is realized in the presence of the normal compressive force, which realizes the contact, as well as of the force pair or of a tangential force. This model can be used on sprocket teeth due to sliding rolling or rolling itself on the gear pole. The results obtained have been experimentally confirmed by many researchers as well as by the damage that the wheels actually suffer from the teeth.

Keyed shear connections with looped U‐bars subjected to normal and shear forces Part I: Experimental investigation

AbstractShear connections in prefabricated concrete buildings are important for the structural performance in both the serviceability and the ultimate limit state. A normal force has a large impact on the shear strength and deformation capacity, however, no experimental record includes compression–shear and tension–shear interaction. This article presents an experimental investigation of keyed shear connections with looped U‐bars subjected to combinations of shear and normal forces. The tests were performed in a custom‐built double frame, where forces could be applied in two perpendicular directions, which was utilized to introduce normal and shear forces. The load combinations ranged from pure tension, over shear–tension and pure shear to shear–compression. The results include load–displacement relationships supplemented by digital image correlation (DIC) results to exemplify the experimental findings and underline the influence of a normal force on the behavior. It was found that a compressive normal force has a positive influence on the shear capacity in the entire displacement domain tested. A tensile normal force reduces not only the shear capacity but also the deformation capacity of the connection. The ultimate shear load was associated with failure in the joint mortar, which in all cases took place as a local key corner shearing. This article constitutes Part I of the investigation, while Part II introduces rigid‐plastic modeling of the ultimate load carrying capacity.

Longitudinal joints of tubbings with newly designed high‐strength reinforcement

AbstractContinuous tunneling using a tunnel‐boring machine is a very popular method when it comes to the construction of large tunnel projects. The use of precast reinforced concrete elements, called tubbings, is a highly economical way to secure the tunnel post excavation. Unfortunately, a loss of the load‐bearing capacity has been observed in the past in the joints between the tubbings. Reasons for that are among others the required reduction of the cross section in the longitudinal joint area and, above all, the high normal compressive forces that arise due to soil pressure. This paper describes experimental testing of longitudinal joints of tubbings conducted at TU Wien. The increase of the load‐bearing capacity of a newly designed and optimized tubbing with high‐strength joint‐compressive reinforcement, which was developed and patented by the Institute of Structural Engineering at TU Wien, is presented. The high‐strength steel is characterized by its high yield strength of 670 MPa, as well as the very large available bar diameters of up to 75 mm. This new optimized tubbing enables the production of thinner tubbings compared to conventional designs, and can thus achieve a reduction in material, transport and excavation costs.

EVALUASI KINERJA STRUKTUR JEMBATAN PELENGKUNG AKIBAT BEBAN GEMPA DENGAN ANALISIS RIWAYAT WAKTU

The behavior of the arch bridge structure has its own peculiarities in distributing loading. The curved shape of the structure allows the structure's own weight to be transferred to the foundation as the normal compressive force without bending. the load is transferred through the semicircular structure to the abutments on either side. The curved (semicircular) design will naturally shift the load received by the floor of the bridge vehicle towards the abutment which keeps both sides of the bridge from moving sideways. Earthquake is a dominant horizontal cyclic loading of a structure. The performance of bridge structures due to the effects of earthquake loading is an important aspect that needs to be taken into account in designing and evaluating the bridge structure. The method used in this study is time history analysis. This article aims to evaluate the performance of arch bridge structures due to earthquake loads by using time-history analysis method. The results of the structure performance show that. The performance of the bridge due to the loading of the Loma prieta earthquake is generated from the period scale that has been analyzed with the 10 second period of the first earthquake for each result. Based on the results of Midas analysis, the strongest location where the damage occurs is in the middle of the bridge road. At the coordinates of 19 the largest displacement is at joint 268 of 1.177169 mm and for U2 of 0.0194 mm and U3 of 31.763771 mm.

Serviceability limits of reinforced concrete hinges

Concrete hinges are monolithic necks in reinforced concrete structures. The serviceability limit states addressed herein refer to the open question how to limit tolerable relative rotations as a function of the compressive normal force transmitted across the neck. Analytical formulae are derived in the framework of the Bernoulli-Euler hypothesis and of Hooke’s law. The usefulness of corresponding dimensionless design diagrams is assessed based on experimental data taken from the literature and on new results from structural testing of reinforced concrete hinges. This way, it is shown that the proposed mechanical model is suitable for describing serviceability limit states. Corresponding design recommendations are elaborated and exemplarily applied to verification of serviceability limit states of the reinforced concrete hinges of a recently built integral bridge. Because the reinforcement is explicitly accounted for, the tolerable relative rotations are larger than those according to the guidelines of Leonhardt and Reimann. Bending-induced tensile macrocracking beyond one half of the smallest cross-section of the neck is acceptable, because the tensile forces carried by the reinforcement ensure the required position stability of the hinges.

THEORETICAL AND FINITE ELEMENT ANALYSIS TO DETERMINE CONTACT PRESSURE, VONMISSES STRESSES AND WEAR IN CAM AND FOLLOWER FOR VARIOUS CAM ROTATIONAL ANGLES IN IC ENGINE

The contact between the cam and follower that exists in the valve strain system of IC engine influences wear. The dynamic analysis of cam and follower system in carried to find the normal compressive force for various cam rotational angles. Based on this compressive force on the cam, the hertz contact stresses and surface wear are calculated theoretically. Finite element analysis was carried out in the three critical portions of the cam such as cam nose region, cam tangent region and cam base circle region to compare the results. The results showed that cam rotational angle directly affects the contact pressure. The max contact pressure occurs in the nose end of the cam. The results showed that principle stress and wear also increases with cam rotational angle

Buckling delamination of a PZT/Metal/PZT sandwich rectangular thick plate containing interface inner band cracks

This work studies the 3D buckling delamination problem around the interface band cracks which are in the PZT/Metal/PZT sandwich rectangular thick plate within the scope of the piecewise homogeneous body model by utilizing the so-called 3D linearized theory of stability loss for piezoelectric materials. It is assumed that the plate is simply supported with respect to mechanical quantities and short-circuit conditions with respect to the electric potential along all its lateral edge-surfaces. On the face planes of the PZT layers, the open-circuit condition with respect to the electrical displacement is satisfied. It is also assumed that on the opposite two ends of the plate which are parallel to the band cracks’ front, uniformly distributed normal compressive mechanical forces act. The critical values of these forces under are determined by employing an initial imperfection criterion. For solution of the corresponding boundary value problems the 3D FEM is utilized and numerical results on the critical forces and on the influence of the problem parameters on these forces are presented and discussed. In particular, it is established that the piezoelectricity of the face layers and the three dimensionality of the problem cause to increase the values of the critical forces.

Effectiveness of Fascial Manipulation on Pain, Grip Strength, and Functional Performance in Chronic Lateral Epicondylitis Patients

Fascial manipulation is an effective tool in the management of the musculoskeletal disorders. This can be used to address pain, grip strength, functional performance in tennis elbow (lateral epicondylitis patients) patients. The specific objective of the study was to evaluate the efficacy of fascial manipulation in tennis elbow its role in decreasing pain , improving the grip strength and overall functional performance is also evaluated. A total of twenty samples participated in the study. Reduction in pain intensity was significant, gaining the fascial connection of the neuromusculoskeletal system may also assist patients in accepting why movement of body parts distant from the site of symptoms may be used as a treatment approach to manipulate fascial tissues. Fascial manipulation techniques are passive manipulations on selected points that focus on restoring the ability of the fascial system to tolerate the normal compressive, friction, and tensile forces associated with daily and sport activities. Question: Role of fascial manipulation in management of chronic lateral epicondylitis. Design: Pre –post experimental study design. Participants: Chronic lateral epicondylitis (tennis elbow) who have pain, decreased grip strength and disturbed functional performance in the Age group 25-40 include both sexes (male and female). Intervention: Fascial manipulation technique on two centers of coordination and one center of fusion, stretching and ultrasound therapy. Outcome measures: Pain and functional performance using Patient Rated Tennis Elbow Evaluation (PRTEE) questionnaire, grip strength was measured using hand dynamometer. Results and conclusion: The result concluded that fascial manipulation is more effective than ultrasound therapy with stretching in the management of lateral epicondylitis subjects and hence it can be effectively used to reduce pain, increase grip strength and functional performance in lateral epicondylitis (tennis elbow) patients.

Finite Element Analysis in different Subtype of Sagittal Alignment

In humans, vertical posture acquisition caused several changes in bones and muscles which can be assumed as verticalization. It’s widely known that six different morphological categories exist; each category differs from the others by pelvic parameters and vertebral column curvatures. Both values depend on the Pelvic Incidence, calculated as the angle between the axis passing through the rotation centre of the two femur heads and the vertical axis passing through the superior plate of the sacrum. The aim of this study is to evaluate the distribution of stress and the resulting strain along the axial skeleton using finite element analysis. The use of this computational method allows performing different analyses investigating how different bony geometries and skeletal structures can behavior under specific loading conditions. A CT of artificial bones, was used to obtain geometrical data of the model developed. Lines were imported into a commercial code in order to interpolate main surfaces and create the solid version of the model. Six different models were created according Roussouly’s classification, by arranging geometrical position of the skeletal components. Loading conditions were obtained by applying muscular forces components to T1 to L5, and a fixed constrain was at the distal epiphisis of femurs. Materials were assumed as elastic; Elastic modulus of 15 GPa, a Shear Modulus of 7 GPa for bony parts; Elastic modulus of 6 MPa, a Shear Modulus of 3 MPa for cartilaginous parts [1]. Six different simulations have been carried out. Results confirm higher solicitations obtained varying configurations from case I to case VI. In particular way, first three cases seem to supply the different loading configurations spreading stresses in almost all the bony parts of the column, while the remaining others three cases produce a higher concentration of stress around the lower part of spine (L3, L4, L5). Results confirm a good agreement with those present in literature, an equivalent Von Mises average stress of 0,55 MPa was found on the intervertebral disks with the higher values reached on the lower part of the model. A comparison of results obtained for Case I with literature, shows a good agreement in terms of normal compressive force, while more evident differences can be found for shear force and sagittal moment. The results underline a relationship between PI increase, and accordingly of PT and LL, and the distribution of load forces. Load forces is exerted mainly on distal vertebrae, especially on L4 and L5.

Performance of Headed Stud on Steel-concrete Composite Bridge Deck as Shear Connector Subjected to Normal Force

The objective of this study was to determine the influence of normal force acting on a steel-concrete composite bridge deck on both the shear stiffness of the headed stud welded on the bottom plate of composite deck and the damage process of the deck. The study also attempted to consider the current design method of headed studs for a composite bridge deck. First, the relationship between shear the force and displacement was obtained from the FE analysis using a model that assumes a part of a bridge deck was exposed to eleven different normal force conditions. Five of these conditions were the compressive, the other five were tensile and the last was without any normal force. The highest shear stiffness was obtained under the normal compressive force condition being equivalent to 50% of the compressive strength of the concrete among the eleven cases. The stress distributions of the bottom steel plate with the normal forces were different from that without any normal force. Furthermore, the restraint conditions of the bottom steel plate were examined in a sensitivity analysis. The analysis concluded that the restraint conditions of the bottom steel plate influence the interlock between the concrete and the headed studs. Full scale model simulating the composite bridge deck in service was built in order to focus on the differences of the carried load by each stud depending on their location on the deck. Static analysis using the full scale model clarified that the stress distribution of the studs itself and the damage state of their surrounding concrete were dependent on their location. Coefficient for the design equation of the headed studs as shear connectors of steel-concrete composite bridge decks was proposed with a consideration of the influence of normal forces and location of each stud.

Selection of Shear Horizontal Wave Transducers for Robotic Nondestructive Inspection in Harsh Environments.

Harsh environments and confined spaces require that nondestructive inspections be conducted with robotic systems. Ultrasonic guided waves are well suited for robotic systems because they can provide efficient volumetric coverage when inspecting for various types of damage, including cracks and corrosion. Shear horizontal guided waves are especially well suited for robotic inspection because they are sensitive to cracks oriented perpendicular or parallel to the wave propagation direction and can be generated with electromagnetic acoustic transducers (EMATs) and magnetostrictive transducers (MSTs). Both types of transducers are investigated for crack detection in a stainless steel plate. The MSTs require the robot to apply a compressive normal force that creates frictional force coupling. However, the coupling is observed to be very dependent upon surface roughness and surface debris. The EMATs are coupled through the Lorentz force and are thus noncontact, although they depend on the lift off between transducer and substrate. After comparing advantages and disadvantages of each transducer for robotic inspection the EMATs are selected for application to canisters that store used nuclear fuel.

Why is it difficult to wash aphids off from superhydrophobic kale?

Many varieties of the cabbage family have leaves covered with superhydrophobic epicuticular wax, which provides them with self-cleaning characteristics. Since the wax also lowers insect adhesion, rinsing of the leaves with water should be an effective way of removing the insects. Conversely, we report that superhydrophobicity of tuscan kale increases resistance of aphids to hydrodynamic removal. The exterior surface of the insects is also superhydrophobic and acts as an extension of the leaf’s surface. As a result even at moderate impact velocities impinging water drops cannot penetrate under the pests. Consequently, liquid impact aids the insect’s adhesion by increasing the normal compressive forces they experience. We show that on a hydrophilic arugula leaf this mechanism is absent, and aphids can be easily washed off with water, as it is able to penetrate underneath them. As for removal of aphids from Tuscan kale, we show that lower surface tension liquids, such as oils and soapy water are more effective, because they are able to wet both the plant and insect surfaces. We also show that aerodynamic removal of aphids consisting of simply exposing the invaded leaf to an air flow is most effective.

Oscillatory squeeze flow for the study of linear viscoelastic behavior

The squeezing of a sample between parallel plates has been used for many years to characterize the rheological behavior of soft, purely viscous materials, and in recent times, small-amplitude oscillatory squeezing has been proposed as a means to determine the linear viscoelastic properties of molten polymers and suspensions. The principal advantage of squeeze flow rheometer over rotational devices is the simplicity of the apparatus. It has no air bearing and is much less expensive and easier to use. Accuracy may be somewhat reduced, but for quality control purposes, it could be quite useful. It might also find application as the central component of a high-throughput rheometer for evaluating experimental materials. The deformation is not simple shear, but equations have been derived to show that the oscillatory compressive (normal) force that is measured can serve as a basis for calculating the storage and loss moduli. These theories as well as instruments that have been developed to generate the required deformation are described, and applications to a variety of materials are described.

Метод нелинейных граничных интегральных уравнений для решения квазистатической контактной задачи о взаимодействии упругих тел при наличии кулонова трения

Рассмотрена пространственная квазистатическая контактная задача о взаимодействии двух линейно-упругих тел с учетом кулонова трения между ними. В граничных условиях задачи на каждом шаге дискретного процесса нагружения были приняты упрощения, основанные на модификации закона трения Кулона. Эта модификация состояла во введении в соотношения, выражающие закон трения Кулона, запаздывания контактных давлений, ограничивающих касательные контактные напряжения. В рассмотренной постановке задача бала сведена к последовательному решению серии однотипных систем нелинейных интегральных уравнений описывающих взаимодействие тел на каждом из шагов нагружения. Для получения контактных напряжений на каждом шаге нагружения использован метод приближeнного решения системы интегральных уравнений этого шага, который заключается в регуляризации этой системы уравнений, дискретизации регуляризированной системы и применении сходящегося итерационного процесса для получения решения дискретизированной системы. Предложенным методом получено численное решение контактной задачи о вдавливании упругого шара в упругое полупространство при возрастании и последующем убывании нормальной сжимающей силы.

Piezotronic Effect in Polarity-Controlled GaN Nanowires.

Using high-quality and polarity-controlled GaN nanowires (NWs), we studied the piezotronic effect in crystal orientation defined wurtzite structures. By applying a normal compressive force on c-plane GaN NWs with an atomic force microscopy tip, the Schottky barrier between the Pt tip and GaN can be effectively tuned by the piezotronic effect. In contrast, the normal compressive force cannot change the electron transport characteristics in m-plane GaN NWs whose piezoelectric polarization axis is turned in the transverse direction. This observation provided solid evidence for clarifying the difference between the piezotronic effect and the piezoresistive effect. We further demonstrated a high sensitivity of the m-plane GaN piezotronic transistor to collect the transverse force. The integration of c-plane GaN and m-plane GaN indicates an overall response to an external force in any direction.