Clamped Area Research Articles

NGHIÊN CỨU PHÂN BỐ ỨNG SUẤT TẠI BIÊN NGÀM CỦA VỎ TRỤ FGM CHỊU TẢI TRỌNG TĨNH SỬ DỤNG LÝ THUYẾT BIẾN DẠNG CẮT BẬC CAO QUASI-3D

This article presents the results of investigating FGM closed cylindrical shells using quasi-3D higher-order shear deformation theory. The law of volume distribution of materials according to the power function. In this article, the results of the analysis of the stress state at the clamped boundary area of the FGM cylindrical shell subjected to radial local loads distributed according to different laws. The mathematical model and the calculation program in Maple are compared and verified with the published results. The article has shown that at the clamped boundary edge, the values of stress components increase sharply, and at the same time, the strong influence of the load parameters (the variation law, the size of the load area), the power-law index on the values and distribution of stress components in the boundary area is demonstrated.

МАТЕМАТИЧЕСКОЕ МОДЕЛИРОВАНИЕ РАСПРОСТРАНЕНИЯ ВИБРАЦИЙ В ТОНКОСТЕННЫХ КАРКАСИРОВАННЫХ КОНСТРУКЦИЯХ. 1. ОСНОВНЫЕ СООТНОШЕНИЯ И АНАЛИТИЧЕСКИЕ РЕШЕНИЯ ХАРАКТЕРНЫХ ЗАДАЧ

The design features of the of thin-walled aerospace, shipbuilding, etc. structures in the form of a load-bearing frame sheathed with thin-walled panels, walls, bulkheads, etc. are discussed. Variants of constructive coupling of the specified thin-walled panels with supporting elements of the load-bearing frame and methods for their mathematical description in the classical mechanics of a deformable solid body are considered. It is proposed, without distorting the physical picture of the dynamic behavior of thin-walled panels, to present them in the form of multisupport thin bars resting on rigid elements of the load-bearing frame along part of their front surface. By the example of a plane dynamic problem of the mechanics of a bar with a fixed section of finite length on one of the front surfaces, it is shown that in the study of deformation processes, taking into account the compliance of the fixed section, it is necessary to introduce the concept of transformation of the stress-strain state parameters and the mathematical models used to describe them. Such a transformation takes place when crossing the border from an unfixed section to a fixed one (from a fixed to an unfixed one). Within the framework of the classical Kirchhoff–Love model, it is impossible to take into account the compliance of the fixed section of the bar, and when using the simplest refined shear model of S.P. Timoshenko, such accounting is possible when fixing the length only on one of the front surfaces. In particular, previously discovered and not described in the scientific literature phenomenon of the vibrations transmission through the support joints, regardless of their design, is carried out due to the transformation of the stress-strain state of the dynamically loaded section of the bar into longitudinal-shear vibration modes of the bar in the clamped area, followed by their retransformation into bending vibrations of the adjacent span. Within the framework of S.P. Timoshenko model, the main resolving equations are constructed, and the kinematic and force conditions for conjugation of fixed and non-fixed sections of the bar are formulated. On the basis of the developed mathematical model, exact analytical solutions of typical problems are constructed, confirming the transmission of vibration through the clamped sections of the bar due to the deformability of the marked sections. A significant increase of transverse shear stresses level in the clamped section of the bar in the vicinity of the junction of the unfixed section with the fixed one is revealed.

Numerical investigation of low-velocity impact in symmetric and asymmetric GFRP laminate with and without pre-crack

Damage induced in symmetrical and asymmetrical glass fiber reinforced polymer (GFRP) laminate overlow-velocity impact (LVI) using a mild steel impactor is investigated. Numerical simulation is done using 3-Dfinite element analysis software LS-DYNA. Orientations for symmetrical and asymmetrical laminate were [(0,90)/(+45,-45)/(+45,-45)/(0,90)//(90,0)/(+45,-45)/(+45,-45)/(90,0)] and [(0,90)/(+45,-45)/(+45,-45)/(0,90)//(+45,-45)/(90,0)/ (90,0)/(+45,-45)] respectively. Two samples each from symmetric and asymmetric laminate with and without pre-crack were numerically simulated. Induced circular pre-crack was modeled in the midplane of the laminate. A circular specimen of radius 75mm with clamped area of 376mm2 is modeled. The velocity of 5 m/sec was assigned to the hemispherical headed cylindrical impactor. The result shows that symmetrical laminates absorb high energy and damage area for it is 24.06 % less than asymmetrical laminate for laminate with pre-crack in mid plate. This study concluded symmetrical laminate design is better for structural purpose as compared to asymmetrical design. Results of proposed investigation are directly applicable in aircraft, automobiles and space equipment. Copyright © 2017 VBRI Press.

Modelling the forming zone of force fitted bending processes

Increasing the flexibility of manufacturing processes is regarded as key challenge for modern production facilities to meet the requirements of market economy. An option to achieve a wide production variety of forming processes is to realize geometrical independence between tools and products. If not bound to tool shape, force transmission from machine to product can be transposed by friction. Because strain is determined by the size and shape of the forming zone, it is hence of crucial interest how the zone develops over the ongoing process. This study presents an analytical approach to study the forming zone of a frictionally engaged, i.e. force fitted, bending process. The model depends parametrically on the mechanical material properties as well as the kinematic parameters with regard to bending angle, clamping pressure and friction. An estimation of the material portion, that is drawn out of the initially clamped area is given by the analytic process model which can thus be deployed to describe strain within the bent arc. For validation purposes, the force fitted in-plane bending process is implemented in a numerical simulation based on solid elements. A significant influence of the material’s hardening properties on the forming zone is observed from the models. With regard to the process, the parameters clamping force and friction coefficient were identified as important influences. With these achievements, the present approach is intended to deliver transferrable knowledge for forming processes, in particular about the areas where tool clamping applies, and thus the impact of strain on geometry, such as the beginning and ending transition zones of a bent arc. In contrast to numerical approaches, the presented analytical model does not require significant computing effort and, with regard to its equations, allows to identify the main influences on strain generated within the forming zone of force fitted bending.

A new design to improve bandwidth of piezoelectric energy harvester

This study proposed a unique wideband energy harvester with a spiral metal plate design which has the potential to harvest vibrational energy over a broad range of ambient frequencies. In this design, metal shim with various length was integrated with piezoceramic rings in a spiral form as the cochlea. Spiral form metal shims with various radius leaves were integrated with piezoelectric ceramic. Each metal leaves has its resonance frequency that is slightly different than its neighboring ones. Parametric studies such as split structure, the radius of the metal shim, brass thickness, and tip mass and clamped area were performed to investigate the energy harvester structure. From the results, the buzzer form energy harvesting unit is designed to split leaf form, resonance frequency shifts to lower frequency. In split structure design for various leaf radius, every leaf keeps their resonance frequencies. This designed structure was resonated on the broader frequency range. Radius difference for neighbor leaves provided wider effective energy harvesting frequency range. Thicker brass shim led to higher stress on piezoelectric ceramic, more significant peak to peak output voltage at own resonance frequency.

A Carrier-Based Discontinuous PWM Method With Varying Clamped Area for Vienna Rectifier

The three-level Vienna rectifier is an attractive topology for power factor correction applications. However, for practical high-frequency applications, the nonlinearity caused by snubber circuit and parasitic capacitance of Vienna rectifier's switching device will distort input current. This paper proposes a carrier-based discontinuous space-vector modulation (CB-DSVM) method with varying clamped area for Vienna rectifier in high switching frequency applications. The equivalent circuit of Vienna rectifier considering the nonlinear factors is built and the effect of pulse shaping around current zero-crossing point is investigated. The voltage errors caused by the nonlinearity of switching device will distort terminal voltage, which mainly appears at the zero-crossing time. A DSVM method with the fixed clamped area around the zero-crossing point is proposed to reduce the voltage errors and then the simplified CB-DSVM method with varying clamped area by adding a clamped factor to the judging conditions is further studied, which will reduce low-order harmonics of the CB-DSVM method. Simulations and experiments are carried out in a 600 W Vienna rectifier platform, which demonstrates the validity of the proposed method. Compared with the CB-SVM method, the proposed CB-DSVM method with varying clamped area has comparative neutral-point voltage balancing ability and better input current quality.

Investigation of chatter stability in high speed milling on thin ribs

Chatter is a self-excited vibration that occurs during high speed machining of parts which is an undesirable phenomenon that affects work piece and also the tool. Chatter mainly depends upon the stiffness, the damping ratio of the material, the force applied and the clamped area. As the machined area continuously changes, the chatter stability of the work piece also changes continuously. The change in natural frequency of Aluminium 7010 T7651 thin rib during milling is calculated by using Modal analysis in ANSYS Workbench. The model is validated with published journal results and experimentally. Also, the scaled-down model of thin rib for same geometry is analysed for any change in natural frequency. The polynomial fit equation for finding instantaneous frequency of thin rib has been found which is applicable for same geometry irrespective of its scale. Using the equation, Stiffness is found and 2D Stability Lobe Diagram has been plotted and chatter free machining has been carried out experimentally in both stable and unstable regions to prove chatter zones. Also it was found that varying spindle speed is easier approach to avoid chatter during milling.

An Analytical Model for Nonhydrostatic Sheet Metal Bulging Process by Means of Polymer Melt Pressure

In this paper, a theoretical approach to model free deformation of sheet metal via polymer injection pressure is presented. It is a general methodology that can be applied for any situation where a nonuniform pressure distribution is responsible for free deformation of sheet metal within a circular cavity. This approach is composed of two iterative approximation loops. In the outer loop, the radius of curvature at the tip of dome shape was optimized based on the boundary condition at the edge of clamped area while in the inner successive loop, principal stresses determined from plasticity theories were used to satisfy the equilibrium equations. While forming sheet metal via polymer injection is a revolutionary yet complex process, its modeling is challenging. Hence, before implementing this general approach to this process, the modeling methodology as such necessitates a simplified solution for melt flow analysis to obtain a pressure distribution encompassing the entire cavity. To evaluate the proposed model, a customized experimental setup was designed and fabricated, which allows sheet metal bulging with the plastic injection. The deformation of the AA1100-O sheet was investigated during the injection of the polypropylene–olefin compound. The comparison of the theoretical and experimental results shows that the general approach formulated here can be successfully applied to predict the surface strains and thickness distributions with maximum error of 6% while the deformed geometry remains within ±0.35 mm deviation in the final deformation stage.

Characterization of mechanical properties of battery electrode films from acoustic resonance measurements

Measurements of the mechanical properties of lithium-ion battery electrode films can be used to quantify and improve manufacturing processes and to predict the mechanical and electrochemical performance of the battery. This paper demonstrates the use of acoustic resonances to distinguish among commercial-grade battery films with different active electrode materials, thicknesses, and densities. Resonances are excited in a clamped circular area of the film using a pulsed infrared laser, and responses are measured using an electret condenser microphone. A numerical model is used to quantify the sensitivity of resonances to changes in mechanical properties. When the numerical model is compared to simple analytical models for thin plates and membranes, the battery films measured here trend more similarly to the membrane model. Resonance measurements are also used to monitor the drying process. Results from a scanning laser Doppler vibrometer verify the modes excited in the films, and a combination of experimental and simulated results is used to estimate the Young's modulus of the battery electrode coating layer.

Su1900 Portal Triad Clamping in Rats, BPC 157 Acutely Protect Blood Vessels in the Intestine and Caecum, and Counteracts Intestinal Lesions. A Comparison With L-NAME and L-Arginine

Background We suggested that the rescue of the blood vessels may be essential for the stable gastric pentadecapeptide BPC 157 as therapy in ulcerative colitis (Curr Med Chem. 2012;19(1):126-32.; Curr Pharm Des. 2011;17(16):1612-32.). Here, we hypothesized that BPC 157 rescues blood vessels in intestinal ischemia injury caused by the portal triad clamping. Of note, depending about the ischemia attenuation or aggravation, the number of blood vessels due to more or less branching may correspondingly decreased (aggravated ischemia) or increase (attenuated ischemia, and rescued blood vessels maintenance), and likewise, anastomosis formation should additionally contribute decreased or increased number of blood vessels presented. A comparison was carried out with the effect of the L-NAME, and L-arginine given alone and/or together. Methods In deeply anaesthetised rats, throughout 30min of the portal triad clamping, in the minute intervals, the assessment involved the most distal part of the ileum, and caecum, 1 cm long, four neighboring vessels where the all arising branches including formed anastomosis between them were all assessed as the total blood vessels number. Besides, medication (/kg) as bath at the clamped area (BPC 157 (10μg, 10ng), L-NAME (5mg), L-arginine (100mg), alone and/or together, was applied at 5min after the portal triad clamping. Results/Discussion At the 30min of the portal triad clamping, controls were presented with fewer branching and anastomosis (intestinum 14.3±1.2; caecum 122.5±5.2), BPC 157 with more branching and anastomosis (intestinum 27.5±3.2; caecum 154.5±7.2, both P<0.05, at least vs. control), markedly less intestine congestion along with few microscopical findings (Figure 1). NO-system agents presented different results, L-arginine a decrease (intestinum 9.2±1.0; caecum 63.3±6.6, both P<0.05, at least vs. control); L-NAME an effect on caecum (intestinum 13.3±2.2; caecum 102.5±5.2, P<0.05, at least vs. control); L-NAME+L-arginine (intestinum 6.3±1.0; caecum 147.5±5.2 both P<0.05, at least vs. control) suggest that these effects are at least partly NO-system related; BPC 157 overcomes the effect of L-arginine (BPC 157+L-arginine (intestinum 33.3±2.2; caecum 183.5±5.2 both P<0.05, at least vs. control); BPC 157+L-arginine+LNAME (intestinum 21.8±2.2; caecum 165.5±5.2 both P<0.05, at least vs. control); its effect was however counteracted by L-NAME: BPC 157+L-NAME (intestinum 14.5±2.2; caecum 106.5±5.2). Conclusions BPC 157 could be used along with portal triad clamping, and may rescue blood vessels in both intestine and caecum, an effect at least partly related to NO-system.

A study on the combined effect of notch and fretting on the fatigue life behaviour of Al 7075-T6

In this study, an investigation was conducted on the fatigue performance of Al 7075-T6 plates in the presence of stress raisers (notch, fretting, and a combination of notch and fretting). Fretting situation was induced on the surface of the aluminium plate through steel contacting pads under two different clamping forces of 2kN and 5.6kN. The fatigue tests revealed a more dominant effect from stress concentrators originating from geometrical discontinuities such as the tested notch compared to the fretting wear conditions. Therefore, no noticeable differences were found between the fatigue lives of the notched specimens and the combined notch and fretting condition. A finite element stress analyses of the notched model under the contacting fretting pads agreed with the experimental results. The stress distribution at the clamped area introduced tensile stresses at the edge of the contact region, however, the stress at the notch tip was observed to be higher when an axial tensile load was applied to the end of the plate. Fractographic analyses confirmed the presence of cracks initiating from the fretting damaged surface for most of the combined notch and fretting fatigue test specimens particularly at the high cycle fatigue (HCF) zone.

Support Losses in Micromechanical Resonators Under Electrostatic and Piezoelectric Actuations

Elimination of support losses has been important in boosting quality factors of micromechanical resonators. A high-quality factor is one of the requirements for the realization of micromechanical resonators applied to modern communication systems, sensors, etc. In this paper, we present theoretical and experimental studies on the support losses in micromechanical resonators driven by electrostatic and piezoelectric actuations separately. We experimentally demonstrate that a piezoelectric actuation can take less support loss than its electrostatic counterpart using an AFM probe actuated by piezoelectric and electrostatic effects, respectively. The study also shows that the energy loss to the support in the piezoelectric resonators could be reduced by decreasing the clamped region area of the piezoelectric material layer on the substrate, and using the piezoelectric material with a smaller ratio of the piezoelectric coefficients along the thickness to the length.

Analytical and numerical modelling of AlGaN/GaN/AlN heterostructure based cantilevers for mechanical sensing in harsh environments

Some industrial areas as oil, automotive and aerospace industries, require electromechanical systems working in harsh environments. An elegant solution is to use III–V materials alloys having semiconductor, piezoelectric and pyroelectric properties. These materials, particularly nitrides such as GaN or AlN, enable design of advanced devices suitable for harsh environment. A cantilever structure based on AlGaN/GaN/AlN heterostructures coupled with a High Electron Mobility Transistor (HEMT) can act as an electromechanical device suited for sensing applications. In this article, we present the mechanical modelling of such a structure. An analytical and a numerical model have been developed to obtain the electrical charge distribution in the structure in response to mechanical stress. A theoretical electromechanical sensitivity of 3.5μCm−2 was achieved for the cantilever free end displacement of several hundreds of nanometres. Both models show good agreement, presenting less than 5% deviation in almost the whole structure. The differences between the two models that are pronounced near the clamped area can be explained by particular boundary conditions of the numerical model. The topological characterization and numerical modelling allowed the estimation of the equivalent intrinsic residual stress in the structure and the stress distribution within each layer. Finally, the dynamic mechanical characterization of fabricated cantilevers using laser interferometry is presented and compared to numerical modal analysis with less than 10% deviation between theoretical and experimental resonant frequencies. The obtained results enable the use of the analytical model for further study of the electromechanical coupling with the HEMT structure.

Graphene-based pressure nano-sensors

We perform atomistic simulations to study the failure behavior of graphene-based pressure sensor, which is made of a graphene nanoflake suspended over a well in a silicon-carbide substrate and clamped on its surrounding edge by the covalent bonds between the graphene flake and the substrate. Two distinct types of mechanical failure are identified: the first one is characterized by complete detachment of the graphene nanoflake from the silicon-carbide substrate via breaking the covalent bonds between the carbon atoms of the graphene flake and the silicon atoms of the substrate; the second type is characterized by the rupture of the graphene nanoflake via breaking the carbon-carbon bonds within the graphene. The type of mechanical failure is determined by the clamped area between the graphene flake and the substrate. The failure pressure can be tuned by changing the clamped area and the well radius. A model is proposed to explain the transition between the two types of failure mode. The present work provides a quantitative framework for the design of graphene-based pressure sensors.

Analytical and numerical modeling of AlGaN/GaN/AlN heterostructure based cantilevers for mechanical sensing in harsh environments

Some industrial areas require functioning electronics in harsh environments. A solution is to use III-V materials alloys having semiconductor, piezoelectric and pyroelectric properties. These materials, particularly nitrides such as GaN or AlN, enable advanced design of devices suitable for harsh environment. A structure based on AlGaN/GaN/AlN cantilevers coupled with a High Electron Mobility Transistor (HEMT) can act as a mechanical sensing device suited to harsh environments. In this article, we present the mechanical modeling of such a device. An analytical and a numerical model have been developed to obtain the electrical charge distribution in the structure. A theoretical electromechanical sensitivity of around 3.5 μC.m−2 could be achieved for a displacement of several hundreds of nanometers. Both models agree considerably well, presenting less than 5% deviation on the whole structure, except near the clamped area, where differences can be explained by particular boundary conditions of the numerical model. The topological characterization and numerical modeling allowed the estimation of the equivalent intrinsic residual stress in the structure and the stress distribution within each layer. The obtained results enable the use of the analytical model for further study of the electromechanical coupling with the HEMT of the structure.

Simulating fretting contact in single lap splices

Cracks in riveted lap splices commonly nucleate in regions of fretting damage around the fastener holes. The crack location is dependent upon the rivet squeeze force and the clamped faying surface area around the holes since fretting damage occurs at the edge of contact. Being able to predict the amount of faying surface clamping from rivet forming and the peaks in edge-of-contact stresses associated with fretting contact will help in the understanding of splice fatigue failure. This paper describes the development of a 3D finite element splice model that predicts the variation of contact area and edge-of-contact stresses in a loaded splice. The prediction is made for four rivet squeeze force levels and both universal and countersunk rivet styles.

Numerical Analysis of Energy Absorption Mechanism in Multi-ply Fabric Impacts

The energy analysis method was employed for the understanding of impact behavior of multi-ply plain-woven fabric considering the energy of a projectile. A three-element viscoelastic model was used to describe the dynamic behavior of fibers. Yarn slippage on the warp-weft crossover points was considered by updating the element length. Crimp effect was taken into account by assigning some portion of the strain to crimp. Fabric slippage on the clamped area and yarn pullout on the edge of the fabric were also considered. Bending resistance of the fabrics was assumed as the reaction force of a node arising from the curvature of the nodes. The inelastic collision of fabric layers as well as the collision with the projectile was considered. The numerical model describing all of the features was implemented as in-house code. Each of the energy dissipation mechanisms was characterized to clarify the contribution to the total energy absorption and performance of the fabrics against ballistic impacts. Three cases representing no-perforation, mature-perforation, and premature-perforation were chosen to explain different energy dissipation characteristics, depending on the impact velocity. The difference in reaction of each layer with projectile was also examined.

Experimental investigation on the bi-directional growing mechanism of the foils laminate approach in AAO fabrication

The foils laminate approach can be implemented to grow bi-directional porous pattern from both the top and bottom surfaces of an aluminum foil. It was intuitively inferred that leakage of etchant from the clamped area can be a feasible cause to have the upward pores grow in the notches of the unpolished surface. This leakage hypothesis has been disproved by the leakage blocking and triple layers laminate experiments. It is further inferred that the non-uniformity of the thickness or material properties of the aluminum foil causes non-uniformed anodization rate along the sample surface. The fast oxidized areas create a pathway for leakage such that a shorter porous array from the back side is observed. Experiments with the process time being reduced by two hours validate this inference

Acid-Sensing Properties in Rat Gastric Sensory Neurons from Normal and Ulcerated Stomach

Gastric acid contributes to dyspeptic symptoms, including abdominal pain, in patients with disorders of the proximal gastrointestinal tract. To examine the molecular sensor(s) of gastric acid chemonociception, we characterized acid-elicited currents in dorsal root ganglion (DRG) and nodose ganglion (NG) neurons that innervate the stomach and examined their modulation after induction of gastric ulcers. A fluorescent dye (DiI) was injected into the stomach wall to retrogradely label gastric sensory neurons. After 1-2 weeks, gastric ulcers were induced by 45 s of luminal exposure of the stomach to 60% acetic acid injected into a clamped area of the distal stomach; control animals received saline. In whole-cell voltage-clamp recordings, all gastric DRG neurons and 55% of NG neurons exhibited transient, amiloride-sensitive, acid-sensing ion-channel (ASIC) currents. In the remaining 45% of NG neurons, protons activated a slow, sustained current that was attenuated by the transient receptor potential vanilloid subtype 1 antagonist, capsazepine. The kinetics and proton sensitivity of amiloride-sensitive ASIC currents differed between NG and DRG neurons. NG neurons had a lower proton sensitivity and faster kinetics, suggesting expression of specific subtypes of ASICs in the vagal and splanchnic innervation of the stomach. Effects of Zn2+ and N,N,N',N'-tetrakis-(2-pyridylmethyl)-ethylenediamine on acid-elicited currents suggest contributions of ASIC1a and ASIC2a subunits. Gastric ulcers altered the properties of acid-elicited currents by increasing pH sensitivity and current density and changing current kinetics in gastric DRG neurons. The distinct properties of NG and DRG neurons and their modulation after injury suggest differential contributions of vagal and spinal afferent neurons to chemosensation and chemonociception.

Experimentally induced ulcers and gastric sensory-motor function in rats.

Prior studies have demonstrated that inflammation can sensitize visceral afferent neurons, contributing to the development of hyperalgesia. We hypothesized that both afferent and efferent pathways are affected, resulting in changes in motor and sensory function. Kissing ulcers (KU) were induced in the distal stomach by injecting 60% acetic acid for 45 s into a clamped area of the stomach. In controls, saline was injected into the stomach. A balloon catheter was surgically placed into the stomach, and electromyographic responses to gastric distension were recorded from the acromiotrapezius muscle at various times after ulcer induction. The accommodation reflex was assessed by slowly infusing saline into the distally occluded stomach. Gastric pressure changes in response to vagal stimulation were measured in anesthetized rats. Contractile function of circular muscle strips was examined in vitro using force-displacement transducers. KU caused gastric hypersensitivity that persisted for at least 14 days. Fluid distension of the stomach led to a rapid pressure increase in KU but not in control animals, consistent with an impaired accommodation reflex. Gastric ulcers enhanced the contractile response to vagal stimulation, whereas the effect of cholinergic stimulation on smooth muscle in vitro was not changed. These data suggest that inflammation directly alters gastric sensory and motor function. Increased activation of afferents will trigger vagovagal reflexes, thereby further changing motility and indirectly activating sensory neurons. Thus afferent and efferent pathways both contribute to the development of dyspeptic symptoms.