Initial Clamping Research Articles

Friction-based connectors with wooden dowels for timber shear walls: Shake table and time-dependent test

Prestressing in wood connection, due to frictional forces, improves mechanical properties of the connection. This paper presents novel friction-based connectors, and corresponding tests at the connection and system levels. The friction-base connector is composed of a softwood or hardwood dowels inserted into the wood-based material and tightened to generate frictional force. Long-term performance was evaluated by stress relaxation tests and time-dependent connection tests. To evaluate dynamic performance of shear walls with friction-based connectors, shake table tests were conducted. The shake table tests showed that the restoring force characteristics of the wood friction shear walls were bilinear reflecting the behaviors of the friction-based connectors. The strength degradation of the wood friction shear walls due to cyclic input was small that more seismic inputs could be applied before any significant damage to the wood friction shear wall. Results of stress relaxation tests, for periods of 1 to 3 years, showed that the stresses were maintained at 70–90% under uncontrolled environment. On the other hand, the results of time-dependent connection tests, for 1 to 6 years, showed high initial clamping stresses caused large performance loss, but high performance could be maintained when tightened below the allowable stress for sustained loading.

Research on movement of dimensional singularities without elastic interaction in gasketed joints

Loss of clamping force due to elastic interaction is unpredictable and nonnegligible with the typical non-linear characteristics of gasketed joints. It is hard to weaken or eliminate elastic interaction by suitable joint dimensions. An analytical model of elastic interaction with dimensional representation is constructed using gasket deformation as a bridge. The influence of multi-dimensional dimensions on clamping force losses, such as bolt spacing, joint width and thickness, was explored by non-linear finite element analysis for a typical sandwich structure with two-bolt gasketed joints. Dimensional singularities without elastic interaction are validated and their approximate range is determined. It is clarified that initial clamping force or joint material can cause dimensional singularity movement. This paper provides a theoretical basis for solving the problem of clamping force losses and inhomogeneities effected by elastic interactions in engineering.

Numerical Study on Slender Circular Reinforced Concrete Column Clamped with Steel Sheet

Various methods to enhance the performance of circular reinforced concrete column have been widely investigated. However, most researches used internal strengthening method such as intensifying steel reinforcement. Others utilized carbon fiber reinforced polymer (CFRP), glass fiber and aramid to retrofit either reinforcement or concrete surface. Few studies incorporated steel to cover concrete surface but neglecting clamp pressure between steel and concrete surface. This study proposes a steel sheet strap strengthening method by initial clamping stress on steel sheets as an external confining technique through experimental works and in-depth numerical analysis. The experimental investigation includes nine steel sheet strengthened reinforced concrete specimens of 20 MPa subjected to axial concentric and axial eccentric. Retrofitting devices will be fabricated from BJ37 steel. Steel sheet straps in each specimen will be subjected to varying initial clamp pressure by fastening bolts. Applied load, lateral displacement and vertical and horizontal deformation will be measured by the instrumentation. Experimental works will observe failure mode, force displacement, stress and ductility. Section analysis based on experimental results will define compatibility equations for numerical stage. Strengthening model from experimental stage will also be analyzed in numerical study with inhouse software 3DNLFEA. F-D curve and moment-curvature loading behavior and ductility will be obtained from numerical analysis. It is believed that the proposed strengthening mechanism with its geometrical and stress variations could enhance the section, member and structural ductility of circular reinforced column against vertical and lateral load. Furthermore, the developed analytical model could well predict the behavior of the proposed clamp mechanism for practical applications.

Effect of Clamping Compression on the Mechanical Performance of a Carbon Paper Gas Diffusion Layer in Polymer Electrolyte Membrane Fuel Cells.

During all the assembly stages of a polymer electrolyte membrane fuel cell (PEMFC) stack, gas diffusion layers (GDLs) endure clamping loads in the through-plane direction several times. Under such complicated assembly conditions, GDLs have to deform with the changes in structure, surface roughness, pore size, etc. A comprehensive understanding of the compressive performance of GDLs at different clamping phases is crucial to the assembly process improvement of PEMFCs. Two typical clamping compression was designed and performed to get close to the actual assembly conditions of PEMFCs. The results indicate that the initial clamping compression and the magnitude of the maximum clamping load have great impacts on the segmented compressive properties of GDLs. The nonlinear compressive performance of the GDL is mainly attributed to the unique microstructural information. The rough surface morphology contributes to the initial compressive characteristics where the big strain along with the small stress occurs, and the irreversible failures such as carbon fiber breakages and adhesive failures between fibers and binders account for the hysteresis between different compression stages. Importantly, it is found that the clamping compression hardly influences the small pore distribution below 175 μm but affects the large pore distribution over 200 μm.

Thermomechanical stability and inelastic energy dissipation as durability criteria for fuel cell gas diffusion media with pre-assembly effects

In this article, pre-assembly hot-press pressure and thermal expansion effects in gas-diffusion layers (GDLs) are addressed to explore the practicalities of the constitutive model reported in the companion article. A facile technique is proposed to include deformation history dependent residual strain effects. The model is implemented in the numerical environment and compared with widely followed conventional models such as isotropic and orthotropic material models. With the normal and accelerated thermal expansion effects no significant variation in stresses or strains is reported with the compressible GDL model in contrast to the conventional incompressible form of the GDL model. The present work identifies the critical differences with advanced and extended variants of the model along with conventional GDL material models in terms of planar stress/strain distribution and the membrane response. Finally, the model is simulated for micro-cyclic stress loads of varying amplitudes that imitate the real working conditions of fuel cell. The inelastic energy dissipation in GDLs is predicted using the proposed model, which is utilized further to distinguish the safe (elastic) and unsafe (inelastic shakedown) operating limits. The inelastic collapse of GDLs is shown to be a active function of high amplitude micro-cyclic load with high initial clamping load.

Features of wear of the elastic half-plane by stamps of the canonical form

For the problems of contact interaction of canons of canonical form (cylindrical, elliptical, hyperbolic, parabolic) with elastic half-plane with consideration of material wear, the features of half-plane wear by different canonical dies at different moments of friction pair time were investigated. An iterative search algorithm based on extrapolation polynomials was used to find wear areas. For fixed moments, the wear areas were numerically calculated at a given initial clamping force. The graphs of the contact pressures were constructed and the peculiarities of their distributions were analyzed for different forms of dies with a considerable time of friction pair operation. As a result of the obtained numerical data, it is established that the contact area changes for canonical stamps depending on the time and curvature of the stamps.

Self-loosening of bolted L-stub connections under a cyclic separating load

This paper presents a combined experimental and numerical study on bolted L-stub connections under simultaneous bending and axial excitation from a cyclic separating load, which has not been reported in the open literatures. The reduction of the clamping force is found from experiments. Additionally, the thread damage is analysed using an optical microscope, a white light interferometer, a scanning electron microscope (SEM) and an energy dispersive X-ray (EDX). The effects of the eccentricity, the excitation level and the initial clamping force on the reduction of clamping force and the damage of threads are also studied in experiments. It is found from the experimental results that the degrees of the thread damage and self-loosening increase with the increases of the excitation level and the eccentricity, and they decrease with the increasing initial clamping force. A three-dimensional finite element model is created to analyse the contact stress and the relative slip between the threads of the bolt and the nut, and the finite element results agree with the experimental measurements.

A Study on Fatigue Strength Improvement for Tension Clamp of Railway Using Work Hardening

Since the tension clamp is essential for the safe operation of trains, the problem of the broken tension clamp must be carefully managed. The damage of the tension clamp can be caused by various reasons such as track conditions and dynamic behaviours of trains. In this paper, the improvement of durability through the improvement of fatigue strength was studied by considering the experiment results and the FE analyses. First, the analytical model was verified by comparing the results of the stress and strain distributions with the initial clamping force and the results of the FE analyses. And then, the method to improve the fatigue strength characteristics was analytically evaluated by considering the behaviour of tension clamp (middle band and spring arm) and work hardening characteristics.

“Non-Touch” Vena Cava Technique as an Improvement in Combined Lung and Liver Procurement in Controlled Donation After Circulatory Death

The number of organs retrieved from donation after circulatory death (DCD) donors has continued to rise in recent years. The functional superiority of DCD organs is achieved when the lungs are perfused with cold perfusion and livers with normothermic regional perfusion (NRP). Thus, a precise surgical technique is required to combine thoracic and abdominal organ procurement.The technique used at our center consists of a rapid laparotomy and middle sternotomy, then the abdominal aorta (Ao) and abdominal inferior vena cava (VC) are cannulated and the descending thoracic Ao is cross-clamped. NRP is started at that point. As a variation of previously described techniques, the thoracic vena cava is not initially clamped in order to improve the return of blood volume to the NRP circuit. The pulmonary artery is cannulated to flush the lungs and the left atrial appendage is opened for drainage. After 120 minutes, NRP perfusion is stopped and the organs are flushed with cold preservation solution.In 2016, 3 livers and 6 lungs were harvested at our center using the technique described. After a minimum follow-up of 1 year, no evidence of biliary complications was observed.The combined procurement of lungs after room temperature perfusion and liver after NRP without initial clamping of the thoracic VC is feasible, with excellent function post-transplantation.

Open surgical approach and technique in left pneumonectomy

The classic posterolateral thoracotomy remains an important incision to any surgeon for lung resections. It allows inspection, complete mobilization of the lung and hilum and access to mediastinal structures. For pneumonectomy, the key-step is the circumferential hilar dissection, exposing the hilar structures, resect lymph nodes and assess resectability in cancer operations. The dissection starts at the level of the left pulmonary artery (PA) and proceeds posteriorly and inferiorly. Suspension of the posterior mediastinum provides excellent exposure of the left main bronchus and the inferior pulmonary vein, while at the same time protects the recurrent nerve and the esophagus. The dissection circumvents the ligament and continues anteriorly, until the superior pulmonary vein is identified and the hilar loop is completed. Isolation of each structure by blunt or even finger dissection commences, and a vascular tape is applied for gentle retraction. The PA is divided first, followed by the inferior and superior pulmonary veins. Either non-absorbable monofilament sutures or staplers may be equally used for the transection of each structure. We suggest initial clamping and then proximal and distal transfixion of the vessels rather than simple ligation if sutures are to be used. Special attention should be paid to the transection of the bronchus, as this step is usually responsible for late complications. The bronchus should be dissected free, up to the level of the carina, retracted, clamped and divided, leaving the shortest possible stump. Either double horizontal mattress sutures or stapler provide equally safe result. The procedure is completed with extended lymph node dissection and air leak assessment.

Analysis Study on Axial Force in Bolted Connection under Fatigue Load

High-strength bolted connection is widely used for steel structure construction. Because high-strength bolted connection has simple constructability and structural qualification. Especially friction type with high-strength bolted connection has high stiffness and fatigue strength. At this time, initial clamping force is one of main factor to affect the strength and deformation behavior of connection. Therefore, the objective of this study is to investigate reduction of initial clamping force in high-strength bolted connection under fatigue load. And the parameter of this study is the size of the bolt and 3 types of initial clamping force. The analysis is used the finite element analysis program ANSYS Workbench.

Loosening analysis for fastening screw of automotive door trim parts

While a screw is a fastening element that can tighten the two parts at low cost, the loosening of the screw is generated due to external forces such as repetitive load, vibration, and thermal stress. This phenomenon decreases the initial clamping force, and this can be a serious problem to the safety of the product. However, while fastening parts are handled through experiment and experience, there is a lack of research on the screw loosening of plastic fastening parts. For example, vehicles have various fastening parts. Among the fastening elements, screws are typically used for tightening parts of the vehicle door trim. Vehicle interior materials are mainly composed of plastic parts. Especially, the temperature of the vehicle interior changes from a sub-zero temperature to 100 degrees (°C) due to solar radiation. Unlike metals, plastic materials are commonly susceptible to the environment. In this study, the fastening screw of automotive door trim parts is selected. First, a screw loosening mechanism is implemented through Computer Aided Engineering (CAE) analysis and the influences of degradation are then analyzed. Secondly, the selecting method of clamping force is suggested through the analysis result of reduction according to the tightening torque.

Friction between a new low-steel composite material and milled steel for SAFE Dampers

This paper describes the development process of a new low-steel composite friction material and the experiments to investigate its frictional behavior. Automotive braking technology was adapted to derive an optimal friction damper for buildings, and a high friction coefficient and stable behavior were set as the primary targets for performance. To improve performance, clamping details which incorporated load washers were also proposed. In order to evaluate the performance of the friction system, pseudo-dynamic tests were conducted. In the experiments, the proposed friction dampers showed repeatable, predictable, and very stable behavior without significant fading of frictional resistance, even under hundreds of repetitive sliding excursions. The friction load tended to be proportional to the initial clamping force regardless of the real-time clamping force, thus confirming that the behavior of the proposed dampers could be predicted using the idealized Coulomb friction model. It was also verified that frictional performance could be remarkably increased through the use of conical shaped load washers, when applied correctly. Furthermore, nonlinear time history analysis was performed on a five-story example building with and without friction dampers. Based on the results, the friction damped system demonstrated effectiveness in reducing structural responses such as roof displacement, base shear force, and story drift ratio compared to the original undamped frame system.

非鉄金属製ボルトの軸直角方向疲労強度への初期締付け力の影響

Accidents due to fatigue of bolted joints frequently occur. In fatigue characteristics of bolts made of high strength steel alloy, it is well-known that the mean stress which is applied on the bolt as clamping force does not have an influence on the fatigue strength. But an influence of the mean stress on fatigue strength for bolt made of non-ferrous materials has not been investigated yet. In this study, transverse fatigue test for two bolted joints made of aluminum alloy A5056 and pure titanium TW340 were conducted to investigate the influence of initial clamping force on transverse fatigue strength. The result showed that transverse fatigue strengths for A5056 bolts and TW340 bolts decreased with an increase in the initial clamping force. It is considered as one of the causes that fatigue fracture origins were different in A5056 bolt and in TW340 bolt.

A theoretical and experimental study on geometric nonlinearity of initially curved cantilever beams

This paper presents a theoretical and experimental study on large deflection behavior of initially curved cantilever beams subjected to various types of loadings. The physical system as a straight cantilever beam subjected to a tip concentrated load is considered in this study. Nonlinear differential equations are obtained for large deflection analysis of such a straight cantilever beam, and this problem is known to involve geometrical nonlinearity. The equations are solved numerically with the help of MATLAB® computational platform to get deflection profiles of the concerned problem. These results are imposed subsequently on the center line of an initially curved beam to get theoretical load-deflection behavior of curved beam problems. To verify the theoretical model, experiment is carried out with the master leaf of a leaf spring bundle by modeling it as an initially curved cantilever beam. The effects of initial clamping and geometry variations in the eye-region are observed from experimental investigation which is commonly neglected in the mathematical formulation. Comparisons of the theoretical results with the experimental results are quite good, but the avenues for further improvement are also reported. The proposed approach is further extended to study large deflection behavior of an initially curved cantilever beam subjected to distributed and combined load. These results are successfully validated with existing results for straight beams and some new results are furnished for initially curved cantilever beams.

Evaluating long-term relaxation of high strength bolts considering coating on slip faying surface

The initial clamping forces of high strength bolts subjected to different faying surface conditions drop within 500 hours regardless of loading, any other external force or loosening of the nut. This study develops a mathematical model for relaxation confined to creep on a coated faying surface after initial clamping. The quantitative model for estimating relaxation was derived from a regression analysis for the relation between the creep strain of the coated surface and the elapsed time for 744 hours. This study establishes an expected model for estimating the relaxation of bolted joints with diverse coated surfaces. The candidate bolts are dacro-coated tension control bolts, ASTM A490 bolt, and plain tension control bolts. The test parameters were coating thickness, species of coating. As for 96, 128, 168, and 226 μm thick inorganic zinc, when the coating thickness was increased, relaxation after the initial clamping rose to a much higher range from 10% to 18% due to creep of the coating. The amount of relaxation up to 7 days exceeded 85% of the entire relaxation. From this result, the equation for creep strain can be derived from a statistical regression analysis. Based on the acquired creep behavior, it is expected that the clamping force reflecting relaxation after the elapse of constant time can be calculated from the initial clamping force. The manufacturer's recommendation of inorganic zinc on faying surface as 75 μm, appears to be reasonable.

Numerical Simulation of Self-Loosening of Bolted Joints under Cyclic Transverse Loads

Self-loosening is one of the major failure reasons for bolted joints. Utilizing the finite element method, a 3-Dimension finite element model under dynamic shear loading is built to study the loosening of bolted fastener phenomenon. And the effect of increment step length, initial clamping force, amplitude of the shear load, thread tolerance, friction coefficients on the loosening process are studied.

OS0303 アルミニウム合金製ボルト締結体の疲労強度における締付け力の影響

In this study, fatigue tests of aluminum alloy bolts have been conducted to investigate the influence of clamping force of the bolted joint on fatigue characteristics. The initial clamping force was set at 2 kN, 4 kN and 6kN. The results showed that the fatigue limits decreased with an increase in clamping force. The results indicate that it was not suitable for aluminum bolts to be tightened with a higher clamping force although the steel bolt has been recommended to be tightened with a higher clamping force.

1102 ボルト締付け時におけるボルト谷底の応力解析と応力集中係数(GS-3 締結要素)

1102 ボルト締付け時におけるボルト谷底の応力解析と応力集中係数(GS-3 締結要素)

Hemodynamic changes in the hepatic circulation after the modulation of the splenic circulation in an in vivo human experimental model

Recent advances in liver surgery have highlighted the effects of the splenic circulation on the hepatic circulation with respect to the hepatic arterial buffer response (HABR). The aim of the present study was to investigate the actual hemodynamic effects of splenic artery embolization/ligation and splenectomy on the hepatic circulation in patients who underwent pancreaticoduodenectomy through in vivo experimental models. In vivo models of splenic artery embolization/ligation (only splenic artery clamping) and splenectomy (simultaneous clamping of both the splenic artery and the splenic vein) were created in 40 patients who underwent pancreaticoduodenectomy for various reasons. The portal venous flow velocity, the portal venous flow volume, the hepatic arterial flow velocity, and the hepatic arterial resistance index were measured with color Doppler ultrasonography. Clamping of the splenic artery induced an immediate and significant increase (16%) in the hepatic artery velocity (P < 0.001), and the portal venous flow also decreased significantly (10%, P = 0.03). Fifteen minutes after the clamping of the splenic artery, the hepatic artery velocity remained significantly increased at the level of the initial clamping, and the portal venous flow significantly decreased (16%, P < 0.001). Clamping of the splenic vein, which was performed after the clamping of the splenic artery, resulted in an immediate and significant decrease (30%) in the portal venous flow (P < 0.001), but the hepatic arterial flow was not affected. Fifteen minutes after the clamping of the splenic vein, there was no change in the portal flow, which remained significantly lower (28%) than the flow in controls, whereas the hepatic arterial flow further significantly increased (31%, P < 0.001). In conclusion, our findings indicate that both splenic artery embolization/ligation and splenectomy are effective for increasing hepatic arterial flow and decreasing portal flow, with splenectomy providing a greater advantage. The HABR underlies these hemodynamic changes.