Residual Clamping Force Research Articles

Experimental Research on Residual Clamping Force of Friction High-Strength Bolt after Corrosion Loss Simulated by Wire Cutting

Experimental Research on Residual Clamping Force of Friction High-Strength Bolt after Corrosion Loss Simulated by Wire Cutting

Shear capacity of corroded high-strength bolted connections

The bolted connection is one of the most commonly adopted connection types in steel structures. The high strength bolted connection is always used in important steel structures. Corrosion is inevitable for bolted connections. To clearly reveal the influence of corrosion on the clamping force of high strength bolts, the stochastic numerical model of randomly corroded bolt connections is established. The whole corrosion process can be simulated through the established stochastic numerical model. The influences of uniform corrosion and random corrosion are analyzed. The change rule of clamping force along with mass loss ratio is analyzed. The random distribution of clamping force corresponding to specific mass loss ratio of bolt head is clarified. The probabilistic distribution of clamping force of randomly corroded bolts is revealed. The simplified numerical model of bolt group connection is proposed. The stochastic numerical analysis can be performed based on this simplified model. The results indicated that it is unsafe if the random pitting corrosion is simplified as uniform corrosion. The corrosion location has obvious on the changing rule of residual clamping force.

A Study on Evaluation Criteria for Self-Loosening of Bolted Joints

In loosening phenomenon of bolted joints (relation between decrease tendency of clamping force and elapsed time), a strong linear relationship on logarithmic coordinates was obtained for mechanical structures with either static loading or dynamic loading, from the research results of authors. By applying this concept to railway bridges, road structures, buildings, etc., prediction of residual loosening lifetime and residual clamping force for loosening failure of bolted joints used for a certain period of time can be feasible. Therefore, it is possible to judge for what extent the bolted joints of the infrastructure used for medium to long term can be used. Furthermore, it is trying to pave the way for presumption of the maintenance time etc. In addition, the results of the study are also shown on criteria for determining whether the remaining clamping force can maintain a proper tightening reliability against loosening.

Residual Clamping Force for Corroded Tension-Control Bolts

AbstractThis study investigated the residual clamping force for corroded tension-control bolts and the effect of each part on force reduction. A finite-element analysis revealed that bolt head sect...

Behavior of slip-critical bolted connections subjected to impulsive loads

Bolted structural steel connections are one of the most common connection types in structures due to their low cost and efficient installation. However, experimental research on the behavior of bolted connections subjected to impulsive loads (e.g., blast, shock, impact) and their residual load carrying capability after the impulse is limited. Most prior research is focused on quantifying the capacity of the bolt material at high rates and less on the energy dissipation of the connection system. In most connections, the bolts are pretensioned to varying levels, which creates a clamping force on the connected members. The friction associated with this clamping force significantly contributes to the overall impulse-resisting force of the system.An experimental program was developed using an impulsive shear apparatus with two loading phases to investigate the effects of friction in slip-critical connections. The objectives of this test series were to collect data to begin to quantify the energy dissipation of an impulsive load through friction, to quantify the residual clamping force, and to determine the force required to initiate slip after such an event. A total of twelve experiments were conducted using the experimental method. This article describes the materials and methods used in the test series, presents the significant findings and observations from the experiments, and discusses key conclusions and recommendations. These initial experiments support the recommendation that structural bolts in relevant structures, including those in bearing-type connections, be installed with the minimum bolt tension required in slip-critical connections, providing a low cost, effective safety measure for protection against extreme loads.

Prediction Method of Residual Lifetime and Residual Clamping Force for Loosening Failure on Bolted Joints

Prediction Method of Residual Lifetime and Residual Clamping Force for Loosening Failure on Bolted Joints

Prediction of residual clamping force for Coulomb type and Johnsen–Rahbek type of bipolar electrostatic chucks

As a key component in semiconductor manufacturing equipment, electrostatic chuck is conventionally divided into Coulomb type and J–R type depending on the generating mechanism of clamping force. After supply voltage is cut off, residual clamping force usually remains and becomes a serious issue for production efficiency and process reliability. Hence, it is significant to propose a general prediction model and reveal changing laws of residual force with time for both types. This paper establishes an equivalent circuit model for a bipolar electrostatic chuck containing distributed embosses on dielectric layer surface, and deduces a unified form of mathematical expression describing decaying force, which can cover the two types. The obtained equations can also predict steady force in working state. Furthermore, an experimental method for measuring clamping force and de-clamping time is presented. The results indicate relative deviations tend to decrease as voltages rise. It is found that prediction precision for J–R type is lower than that for Coulomb type. Main reasons are explained and relevant mechanisms are discussed. Overall, the calculations coincide with the measurements within an acceptable error range. The comparisons suggest the theoretical model is effective for simulating the characteristics of residual clamping force for both types of electrostatic chucks.

Residual clamping force of bolt connections caused by sectional damage of nuts

To consider sectional damage of bolt connections by corrosion damage for the maintenance of steel structures, the residual clamping force of bolt connections was quantitatively examined depending on sectional damage of the nut sections developed from artificial cutting in this study. Thus, friction connection specimens using high-strength bolt connections were fabricated, and the nut sections in the bolt connections were artificially damaged using handheld cutting tools. To measure the change in the clamping force of the bolt connections, the change in strain measured in the bolt using a strain gage was examined after clamping and inducing artificial sectional damage to the nut. The bolt size and the shape and extent of sectional damage were the parameters considered in this study. The weight of the nut was measured after inducing artificial sectional damage to nut to calculate induced sectional damage of nut. From tests results for bolt connection with artificial sectional damaged nuts. The residual clamping forces of the bolt connections were decreased because of the reduced tensile resistance of the bolt connections, affected by the sectional damage of the nut. In case of high sectional damage in the nut section, a relatively higher change in the clamping force was found in the tested series of nuts. From regression analysis of the residual clamping force of the bolt connections, the estimation equations for the change in the residual clamping force developed from sectional damage of the nut were formulated using the damaged volume of the nut and diameter of the remaining nut section for the maintenance of bolt connections in steel structures.

Residual Clamping Force and Dynamic Random Access Memory Data Retention Improved by Gate Tungsten Etch Dechucking Condition in a Bipolar Electrostatic Chuck

Residual Clamping Force and Dynamic Random Access Memory Data Retention Improved by Gate Tungsten Etch Dechucking Condition in a Bipolar Electrostatic Chuck

Residual Clamping Force and Dynamic Random Access Memory Data Retention Improved by Gate Tungsten Etch Dechucking Condition in a Bipolar Electrostatic Chuck

It was found that the residual clamping force of bipolar electrostatic chucks created by the residual charge between a wafer and an electrode would not only cause a wafer sticking problem but also degrade dynamic random access memory (DRAM) data retention performance. The residual clamping force and data retention fail bit count (FBC) of DRAM showed strong correlations to the gate tungsten etch dechucking process condition. Wafer sticking only degraded DRAM cell retention performance, and did not influence any in-line measurement or electrical parameters. Electrical characterization analysis of the FBC proved that the retention loss was mainly due to junction leakage rather than gate-induced-drain-leakage current. A new approach was proposed to suppress this leakage by introducing N2 gas instead of O2 to supply more plasma charges for neutralizing the wafer surface residual charges. The wafer shift dynamic alignment (DA) offset and retention FBC could be reduced by 50 and 40%, respectively. Poor data retention was suspected because of the compressive stress caused by wafer sticking DA shift resulting in a high electric field at the junction and an increase in junction leakage at the storage node.

Generation mechanism of residual clamping force in a bipolar electrostatic chuck

Clamping and residual clamping forces of a Johnsen–Rahbek-type (JR-type) bipolar electrostatic chuck (ESC), which has electrically independent dual electrodes, were measured. Area ratios of the ESC’s two electrodes ranged from 1 to 4.6. It was found that the clamping force per unit area decreases with increasing area ratio and that the residual clamping force per unit area increases with increasing area ratio. To reveal the mechanism of residual clamping force, an equivalent circuit model of a JR-type bipolar ESC was devised. The model showed that the residual clamping force is caused by the residual charge that results from the charge difference in two monopolar ESCs. The charge difference is due to the resistance dependency on voltage of the dielectric layer of the ESC. The wafer voltage calculated from the model agreed well with the voltage measured by an electrostatic voltmeter. It can be concluded that the model is suitable for simulating the performance of a bipolar ESC.

双極型静電チャックの特性評価

The electrostatic chuck (ESC) is being applied to the wafer stages for various kinds of semiconductor-manufacturing machines. This is because the ESC can control the wafer temperature very precisely if helium backside gas is used at the same time. The basic components of the ESC are an electrode and a dielectric layer. The wafer is attracted to the dielectric layer by the coulomb force generated from the electric charge when DC voltage is applied betwween the electrode and wafer. However, a residual clamping force remains if a charge remains after DC votage release. Preventing this residual clamping force is a key to using the ESC because it degrades wafer throughput. We have examined how this clamping force degrades the performance of a bipolar ESC with electrically independent dual electrodes. The cause of the residual clamping force was studied on the basis of an equilibrium circuit of ESC.

Investigations of Bolt Loosening Mechanisms : 3rd Report, On the Bolts Tightened over Their Yield Point

With regard to the bolts tightened over their yield point and subjected to the tensile load, the relation between the load and the residual bolt clamping force after unloading as theoretically analyzed, and a static bolt loosening test was carried out. It was verified that the theoretical results coincide very well with the results of experiments. And under the same condition a fatigue test was carried out with the measurement of the bolt clamping force, and the following results were obtained : (1) Except the loss in the initial stage, there is no loss of the clamping force. (2) With an increase of the initial clamping force, the residual clamping force and also the bolt fatigue life increase. So, judging from the above results, the tightening of bolts over their yield point has an advantage over the tightening of bolts below their yield point.

Effects of Variations in the Screw Thread Coefficient of Friction on the Clamping Force of Bolted Connections

When load is applied to a bolted connection in the direction of the bolt axes, the residual clamping force on the joint is dependent upon the pretension of the bolt. Where bending action is also present, the fluctuating stress in the bolts may also be dependent upon the pretension. In most cases where an accurate pretension is required, the bolts are tightened by means of a torque spanner, and the pretension is then dependent upon the coefficient of friction between the screw threads of the nut and bolt. The effect of normally distributed variations in the coefficient of friction on the pretension is considered.