Clamp Design Research Articles

The Influence of Clamping Pressure on Joint Formation and Mechanical Performance of Ti6Al4V/CF-PEEK Friction-Riveted Joints.

This work aims at investigating the influence of pre-set clamping pressure on the joint formation and mechanical strength of overlapping direct-friction-riveted joints. A pneumatic fixture device was developed for this work, with clamping pressure varying from 0.2 MPa to 0.6 MPa. A case study on overlapping joints using Ti6Al4V rivets and woven carbon fiber-reinforced polyether-ether-ketone (CF-PEEK) parts were produced. Digital image correlation and microscopy revealed the expected compressive behavior of the clamping system and the continuous pressure release upon the joining process owing to the rivet plastic deformation and the polymer squeezing flow. Two preferential paths of material flow were identified through the alternate replacement of the upper and lower composite parts by a poly-methyl-methacrylate (PMMA) plate—the composite upward and squeezing flow between the parts which induced their separation. The ultimate lap shear forces up to 6580 ± 383 N were achieved for the direct-friction-riveted CF-PEEK overlap joints. The formation of a gap to accommodate squeezed polymer between the composite parts during the process had no influence on the joint mechanical performance. The increase in the clamping pressure for joints produced with a low friction force did not affect the joint-anchoring efficiency and consequently the joint strength. On the other hand, the combined effect of a high-friction force and clamping pressure induced the inverted bell shape of the plastically deformed rivet tip, a lower anchoring efficiency, and the delamination of the composite, all of which decrease the mechanical strength by 31%. Therefore, the higher the friction force and clamping pressure, the more defects would be generated in the composite parts and the more changes in the shape of the plastically deformed rivet tip, leading to a lower level of quasi-static mechanical performance. All the joints failed by initial bearing of the composite and final rivet pull-out. The findings of this work can contribute to further improvement of the clamping design for industrial application.

3D Printed Clamps to Study the Mechanical Properties of Tendons at Low Strains

Various clamp designs have been proposed over the years with different degrees of complexity and actual performance vis‐à‐vis correct grip and reduced impact on the surface strains of the tendon sample. The previous studies all focused on impact on ultimate tensile strain and Young's modulus of the tendons. Here an innovative clamp design is proposed that utilizes the fairly recently available technology that is 3D printing to produce a made‐to‐measure tendon sleeve that encloses the sample ends and also enables straightforward alignment within the testing equipment. All experiments are carried out using the superficial digital flexor tendons obtained from pig hind legs. The Young's moduli for the linear region of the tendon obtained using this clamp design are very similar to those obtained using the cryo Jaw by other researchers for the same tendon. Furthermore, negative Poisson's ratios are also obtained for the toe‐region, in agreement with previous work.

Equivalent Stiffness Model of a Proton Exchange Membrane Fuel Cell Stack Including Hygrothermal Effects and Dimensional Tolerances

Proton exchange membrane fuel cells (PEMFCs) require mechanical compression to ensure structural integrity, prevent leakage, and to minimize the electrical contact resistance. The mechanical properties and dimensions of the fuel cell vary during assembly due to manufacturing tolerances and during operation due to both temperature and humidity. Variation in stack compression affects the interfacial contact pressures between components and hence fuel cell performance. This paper presents a one-dimensional equivalent stiffness model of a PEMFC stack capable of predicting independent membrane and gasket contact pressures for an applied external load. The model accounts for nonlinear component compression behavior, thickness variation due to manufacturing tolerances, thermal expansion, membrane expansion due to water uptake, and stack dimensional change due to clamping mechanism stiffness. The equivalent stiffness model is compared to a three-dimensional (3D) finite element model, showing good agreement for multicell stacks. Results demonstrate that the correct specification of gasket thickness and stiffness is essential in ensuring a predictable membrane contact pressure, adequate sealing, and avoiding excessive stresses in the bi-polar plate (BPP). Increase in membrane contact pressure due to membrane water uptake is shown to be significantly greater than the increase due to component thermal expansion in the PEMFC operating range. The predicted increase in membrane contact pressure due to thermal and hydration effects is 18% for a stack containing fully hydrated Nafion® 117 membranes at 80 °C, 90% relative humidity (RH) using an eight bolt clamping design and a nominal 1.2 MPa assembly pressure.

Superposition method to reduce the computation time in shape-memory alloy–based tool clamp design

Recent developments in small hard components, such as those used in medical devices, have led to more stringent requirements of the machining process. Many high-precision technologies have been dev...

The effect of clamping conditions on tearing energy estimation for highly stretchable materials

A typical measure for the toughness of highly stretchable materials is the energy for tearing, determined in mode I fracture tests on wide specimens with a lateral cut. In the present paper we show that, when slippage occurs in the grips that hold the specimens, the classical analysis of this test leads to an overestimation of the tearing energy, if sample stretches are determined from the grip displacements. Unlike for elastic properties, the use of local strain data retrieved by an optical measurement system does not remedy this issue but, vice versa, underpredicts the tearing energy. Here we propose a simple post hoc correction of the measured tearing energy, and an improved clamp design to prevent slippage. Applied to a commercial acrylic elastomer, the corrected tearing energy was independent of the occurrence of slippage and consistent with the result obtained with the new clamping system as well as values reported in literature.

Low-Leakage ESD Power Clamp Design With Adjustable Triggering Voltage for Nanoscale Applications

A low-leakage electrostatic discharge power clamp with adjustable triggering voltage ( ${V}_{t1})$ is proposed in this paper. By enabling the static detection path using the transient one, the proposed clamp achieves a wide range of adjustable ${V}_{t1}$ while maintaining low standby leakage current ( ${I}_{\text {leak}})$ , which overcomes the flaw of traditional static clamps. Besides, the adjustable ${V}_{t1}$ with low ${I}_{\text {leak}}$ is attractive for nanoscale applications. Moreover, the proposed clamp achieves enhanced false-triggering immunity over traditional transient clamps. The proposed clamp is successfully verified in a 65-nm CMOS process. Aside from silicon verifications, detailed comparisons with prior arts and practical application concerns are also addressed in this paper.

BGA substrate outgassing negative impact study on Cu wire bonding

PurposeThe purpose of this paper is to attempt to study the failure mechanism of BGA (ball grid array) Cu wire bond ball lift and specifically focused on substrate outgassing’s impact on Cu wire bonding quality and reliability.Design/methodology/approachThe Galvanic corrosion theory has been widely adopted in explaining the failure mechanism of Cu ball bond lift issue during reliability test or field application in the presence of moisture. In this study, ion chromatography was performed on BGA substrate halogen analysis. EDX (energy-dispersive X-ray spectroscopy) was also used to detect the contaminant’s element at the bottom surface of a window clamp. Further FTIR (Fourier transform infrared spectroscopy) analysis verified that the contamination is from substrate outgassing during wire bonding. A new window clamp design proved effective in reducing the negative impact from substrate outgassing during wire bonding.FindingsThe solder mask in a fresh substrate contains a chlorine element. The chlorine can be detected in the BGA substrate outgassing during wire bonding by FTIR and EDX analyses, which have a negative impact on the Cu wire bonding. The window clamp with a larger opening can reduce the negative impact of the Cu wire bonding from the BGA substrate outgassing.Research limitations/implicationsBecause of the limitation of time and resources, bonding pad surface contamination from substrate outgassing and its correlation with Cu bonding ball lift failure after reliability test will be studied in depth later.Originality/valueThe BGA substrate outgassing has negative impacts on Cu wire bondability. A window clamp with a larger opening can reduce the negative impact from substrate outgassing.

A Novel Cascade-Free 5-V ESD Clamp Using I-MOS: Proposal and Analysis

In this paper, we present a new ESD device using the p-channel impact ionization MOSFET (I-MOS) with its gate and source connected to the ground, and its drain connected to the input/output (I/O) pad, called as the gate grounded I-MOS (GGIMOS). The proposed GGIMOS uses the conventional thick oxide (used for 2.5-V I/O devices) for 5-V failsafe/fault-tolerant I/O applications. For positive electrostatic discharge (ESD) stress, the turn-on mechanism is through controlled avalanche multiplication. During negative stress, the GGIMOS acts as a forward-biased gated diode. The gate oxide reliability concern of the p-channel I-MOS is alleviated by implementing the device in the p-substrate instead of n-well. The physics and operation of the GGIMOS is explained using electrothermal technology computer-aided design simulations and its performance is benchmarked using the simulated transmission line pulsing (TLP), very fast TLP, and human body model results. The proposed device eliminates the need for: 1) a cascaded nMOS architecture for high-voltage capability; and 2) a return diode for negative ESD stress conditions resulting in an area-efficient ESD clamp design. This makes the GGIMOS a potential device for ESD clamping applications in the state-of-the-art CMOS technologies.

Integrated tuning fork nanocavity optomechanical transducers with high fMQM product and stress-engineered frequency tuning

Cavity optomechanical systems are being widely developed for precision force and displacement measurements. For nanomechanical transducers, there is usually a trade-off between the frequency (fM) and quality factor (QM), which limits temporal resolution and sensitivity. Here, we present a monolithic cavity optomechanical transducer supporting both high fM and high QM. By replacing the common doubly clamped, Si3N4 nanobeam with a tuning fork geometry, we demonstrate devices with the fundamental fM≈29 MHz and QM≈2.2×105, corresponding to an fMQM product of 6.35×1012 Hz, comparable to the highest values previously demonstrated for room temperature operation. This high fMQM product is partly achieved by engineering the stress of the tuning fork to be 3 times the residual film stress through clamp design, which results in an increase of fM up to 1.5 times. Simulations reveal that the tuning fork design simultaneously reduces the clamping, thermoelastic dissipation, and intrinsic material damping contributions to mechanical loss. This work may find application when both high temporal and force resolution are important, such as in compact sensors for atomic force microscopy.

A novel monolithic piezoelectric actuated flexure-mechanism based wire clamp for microelectronic device packaging.

A novel monolithic piezoelectric actuated wire clamp is presented in this paper to achieve fast, accurate, and robust microelectronic device packaging. The wire clamp has compact, flexure-based mechanical structure and light weight. To obtain large and robust jaw displacements and ensure parallel jaw grasping, a two-stage amplification composed of a homothetic bridge type mechanism and a parallelogram leverage mechanism was designed. Pseudo-rigid-body model and Lagrange approaches were employed to conduct the kinematic, static, and dynamic modeling of the wire clamp and optimization design was carried out. The displacement amplification ratio, maximum allowable stress, and natural frequency were calculated. Finite element analysis (FEA) was conducted to evaluate the characteristics of the wire clamp and wire electro discharge machining technique was utilized to fabricate the monolithic structure. Experimental tests were carried out to investigate the performance and the experimental results match well with the theoretical calculation and FEA. The amplification ratio of the clamp is 20.96 and the working mode frequency is 895 Hz. Step response test shows that the wire clamp has fast response and high accuracy and the motion resolution is 0.2 μm. High speed precision grasping operations of gold and copper wires were realized using the wire clamper.

Design of a Portable IPMC Actuator Tester

As a new intelligent material, IPMC (Ionic polymer-metal composite) can be driven under low voltage with large deformation, and has been widely used in biomedical and robotic systems. Traditional IPMC testing system is bulky, high cost, and inconvenient to use. In order to achieve the portability and convenience of the IPMC testing system, a small and low-cost IPMC tester was designed. The power supply and control system of the tester were integrated into an IPMC electrode clamp. The main research work included control system circuit design, electrode clamp and overall exterior design. The displacement measurement results showed that the design for the IPMC tester was correct and feasible.

Design Method of a New Type of Expansive Stressed Grouted Clamp

Considering the different mechanism of self-stress formation, a new type of structure was proposed for expansive grouted clamp, which is used for underwater repair on steel tubular. Since the structure is changed totally, the corresponding design method should be modified. This paper summarizes a design method of the new type of expansive stressed grouted clamp and sorts out a set of practical design procedure for the new structure. The core principles of the design method are based on the checks on slip capacity, member crushing and structural strength, associated with the experiment data and previous design experience as reference. An example of such clamp design for repairing a horizontal brace of a jacket platform is also introduced to describe how this method works.

Automatic Process Intermediate Model Generation in Process Planning

In process planning of machined part, three-dimensional process intermediate models are necessary for process design, documentation, and downstream applications including clamping design, NC programing, and process analysis. An automatic process intermediate model generation method is proposed in this paper for machined part represented in B-Rep solid model. Machining features are recognized and classified according to process type. Process plan is expressed in terms of machining features and feature surface modification operations in solid model. Local modification operations are applied to part model to move, replace or remove feature surface resembling machining process. Process intermediate models are generated automatically in a batch manner by applying geometry and topology modification operations directly on B-Rep model for each machining operation. The proposed algorithm is implemented in a CAPP tool developed in solid modeler ACIS.

The Hot-Plugging Clamp Design of the Petrochemical Equipment Pipeline

Liquid leaking accidents of petrochemical equipment were always happened in weld joint of the pipeline. In order to deal with the accidents, the hot-plugging technique was adopted. And the clamp design which was the difficult point of this technology must be valued. In this paper, the hot-plugging technique and the structure of the clamp were introduced. And the calculation formula of the clamp thickness was deduced based on the influence of the injecting hole on the clamp and GB150-98. And the results would be the fundament of further study of the hot-plugging clamp design

In-plane flexure-based clamp

► Simple flexure-based clamp to hold cylindrical and flat components in the plane of a mounting plate. ► Provides well-distributed clamping force while avoiding localized stress concentration. ► Simple to fabricate using standard machining processes. ► Provides self-aligning and self-correcting capabilities. ► Closed-form and finite elements analyses provide insight into the clamp performance. This paper presents the design of a simple flexure-based clamp that may be used in experimental set-ups to hold cylindrical and flat components in the plane of a mounting plate. While it is easy to clamp cylindrical components normal to the plane of a mounting plate, effective in-plane clamp designs are relatively less common due to practical fabrication challenges. The proposed design provides a well-distributed clamping force while avoiding localized stress concentration, and is simple to fabricate using standard machining processes. Additionally, it allows adjustability in the axial position of the component being held prior to clamping, and also provides self-aligning and self-correcting capabilities. Several examples where this clamp design has been successfully employed are presented. A simple model is developed to provide physical and analytical insight into the relation between the clamp's geometric dimensions and performance. These results are validated via finite elements analysis. Several alternate in-plane clamp designs are also proposed.

UG Software CAD/CAM Technology in Shark Model Processing Application

The first use of UG modeling tool to complete the shark 3D modeling; then using UG software to complete the automatic programming automatic programming function, and generates 3 axis machining program, then use the Yulong NC simulation software for NC machining simulation, validation procedures for the procedure to import CNC machine tool by processing, difficulty of shark processing fashion clamp design and processing.

Arterial clamping: Finite element simulation and in vivo validation

Commonly used techniques in cardiovascular interventions such as arterial clamping always entail a certain degree of unavoidable iatrogenic tissue damage. Therefore, studies have been directed towards the decrease of undesired intraoperative trauma, for example, through the design of less traumatic surgical instruments. Obviously, the effectiveness of new clamp designs and techniques depends on how well damage mechanisms are understood and how accurate thresholds for safe tissue loading can be set. This information can in part be derived from reliable finite element simulations. This study is the first to describe a finite element simulation of the clamping of a rat abdominal aorta with occlusion and in vivo validation. Material nonlinearity, large deformations, contact interactions and residual strains are hereby taken into account. The mechanical parameters of the model are derived from inflation experiments. The effect of the residual strains, different clamp geometries as well as the effect of variations in material properties are studied. In all simulations, stress concentrations in different regions of the tissue are noticed, especially for a corrugated clamp design. This shows the importance of finite element modeling in understanding the relation between mechanical loading and damage mechanisms. The inclusion of residual strains has its effect not only in the physiological loading regime, but also during clamping. Just as in the physiologic regime, it lowers the stress gradients through the wall thickness. Varying the material properties with the measured standard deviation between specimens leads to an average change of ±17% in the maximum and minimum principal stresses. Finally, the model is validated with an in vivo clamping experiment on a Wistar rat in which the clamping force was measured, showing good correspondence with the modeled clamping force.

A Novel Experimental Device for Seebeck Coefficient Measurements of Bulk Materials, Thin Films, and Nanowire Composites

An experimental setup has been designed and built for measuring the Seebeck coefficient of bulk thermoelectric materials, thin films, and nanowire composites in the temperature range 200–350 K. The setup utilizes a differential method for measuring the Seebeck coefficient of the sample. The sample holder is a simple clamp design, utilizing a spring-loaded mounting system to load and hold the sample between two copper blocks, on which the electrical leads, as well as thermocouples, are mounted. The spring-loaded design also offers fast turn-around times, as the samples can be quickly loaded and unloaded. To measure the Seebeck coefficient, a temperature difference is generated across the sample by using four 10 kΩ resistive heaters mounted in series on one of the copper blocks. The resulting slope of the thermo-emf versus temperature difference plot is used to obtain the Seebeck coefficient at any temperature. Test measurements were carried out on bulk samples of nickel (Ni), bismuth-telluride (Bi2Te3), antimony-telluride (Sb2Te3), as well as thin films and nanowire composites of Ni.

Fluid–structure interaction in aortic cross-clamping: Implications for vessel injury

Vascular cross-clamping is applied in many cardiovascular surgeries such as coronary bypass, aorta repair and valve procedures. Experimental studies have found that clamping of various degrees caused damage to arteries. This study examines the effects of popular clamps on vessel wall. Models of the aorta and clamp were created in Computer Assisted Design and Finite Element Analysis packages. The vessel wall was considered as a non-linear anisotropic material while the fluid was simulated as Newtonian with pulsatile flow. The clamp was applied through displacement time function. Fully coupled two-way solid–fluid interaction models were developed. It was found that the clamp design significantly affected the stresses in vessel wall. The clamp with a protrusion feature increased the overall Von Mises stress by about 60% and the compressive stress by more than 200%. Interestingly, when the protrusion clamp was applied, the Von Mises stress at the lumen (endothelium) side of artery wall was about twice that of the outer wall. This ratio was much higher than that of the plate-like clamp which was about 1.3. The flow reversal process was demonstrated during clamping. Vibrations, flow and wall shear stress oscillations were detected immediately before total vessel occlusion. The commonly used protrusion clamp increased stresses in vessel wall, especially the compressive stress. This design also significantly increased the stresses on endothelium, detrimental to vessel health. The present findings are relevant to surgical clamp design as well as the transient mechanical loading on the endothelium and potential injury. The deformation and stress analysis may provide valuable insights into the mode of tissue injury during cross-clamping.

Optimal disk clamp design to minimize stress variation of disks in a hard disk drive

To avoid disk waviness and warpage in a hard disk drive, it is desirable for the stress distribution on disks fastened to a spindle motor by a clamp to be uniform in the circumferential direction while sufficient clamping force is maintained. The objective of this work is to find a clamp configuration that minimizes the circumferential stress variation on the disks while maximizing the clamping force. Topology and shape optimization methods were employed to find the optimal clamp configuration. To facilitate the optimization problem, a model for the surface contact between the clamp and the top disk was simplified to a static model where the disk clamp and spring were connected. By incorporating the surface recess, the optimized clamp has equal stiffness in the circumferential direction, except for the four tooling hole areas. Numerical simulation confirmed that the optimized clamp reduced the stress variation by about 78% without sacrificing the clamping force; in fact, it increased the clamping force.