Slippage Load Research Articles

Load extension behavior of spun sewing threads on seam slippage

The present research is focused to develop the relationship between the seam slippage and mechanical properties of sewn fabric by considering the spun thread and fabric configuration in the stitched assembly. Plain and twill weave fabric was used for the sample development stitch with the spun thread while the sewing machine setting was kept constant to produce a balanced seam. Different stitched samples are prepared in warp and weft direction for investigation by considering superimposed, flat, and bound seam classes with multi-thread chain, lock, and cover stitches. Experiment findings highlight the optimum load of seam slippage in N at 6 mm seam opening at stitched assembly by employing mentioned seam classes and stitch types. The results showed that 189.97 N maximum load was found at 6 mm seam opening for plain weave fabric in warp direction at flat seam sample with a lock stitched while in weft direction 80.65 N minimum load at the bound seam with multi-thread chain stitch. For twill weave fabric 94.72 N minimum slippage load at a 6 mm seam opening was observed in the weft direction at the bound seam with multi-thread chain stitch while in the warp direction maximum slippage load of 200 N was reported at the superimposed, flat and bound seam with multi-thread chain, lock and cover stitches. Established findings have a significant coefficient of determination (R2 0.90) between sewing thread extension and seam slippage load at 6 mm seam opening in both directions. The present research provides the guidelines to select the spun sewing thread which was possessed the minimum extension (%) against the respective load (N) to overcome the seam slippage in the stitched garment.

Reduction of Stress Concentration at Stop-Hole by Bolting a Crack

A stop-hole, which is drilling at the crack tip, is one of the famous tentative repairs of fatigue cracks in steel structures. When the crack becomes longer, the stress concentration of the stop-hole also increases. Therefore, during the tentative repair of long fatigue cracks, the chances for re-initiation of the fatigue cracks from the stop holes are high. The bolting stop-hole method is a useful technique against fatigue cracks. In this technique, bolting is applied only for the stop-holes at the crack tips. Therefore, as the crack length increases, the effect of the bolting stop-hole method decreases. In this paper, the authors propose a stress concentration reduction technique for a stop-hole by bolting the fatigue crack between stop-holes. The effect of the proposed technique was verified by tensile and bending tests of specimens as well as finite element analysis. From the tensile and bending tests, it was clarified that the stress concentration of the stop-hole was drastically reduced by bolting a crack under the condition before the slippage of bolts. Additionally, multi-bolting cracks have the advantage of improving the slippage load of the bolts in a crack. Furthermore, finite element analysis verified the reduction in stress concentration of the stop-hole by bolting a crack, and the effectiveness of bolting cracks and stop-holes was also shown.

The study of frictional damper with various control algorithms

Frictional dampers are used in structural engineering as means of passive control. Meanwhile, frictional damper shave a disadvantage compared to viscous rivals since the slippage force must be exceeded to activate the device, and cannot be ideal full range of possible events. The concept of semi-active control is utilized to overcome this shortcoming. In this paper, a new semi-active frictional damper called Smart Adjustable Frictional (SAF) damper is introduced. SAF damper consists of hydraulic, electronic units and sensors which are all linked with an active control discipline. SAF acts as a smart damper which can adapt its slippage threshold during a dynamic excitation by measuring and controlling the structural response. The novelty of this damper is, while it controls the response of the structure in real time with acceptable time delay. The paper also reports on the results of a series of experiments which have been performed on SAF dampers to obtain their prescribed hysteretic behavior for various control algorithms. The results show that SAF can produce the desired slippage load of various algorithms in real time. Numerical models incorporating control simulations are also made to obtain the hysteretic response of the system which agrees closely with test results.

Seismic response sensitivity of the structures equipped with cylindrical frictional dampers to the value of slippage load

Seismic response sensitivity of the structures equipped with cylindrical frictional dampers to the value of slippage load

Experimental and numerical study of a new adjustable frictional damper

In this paper, the concept of a semi active frictional damper called Adjustable Frictional Damper (AFD) is introduced. The clamping force of such damper is secured by hydraulic pressure, which not only reduces the manufacturing costs but also makes it possible to control the seismic response of the structure by changing the clamping force of the dampers.The hysteretic behavior of AFD is studied by experimental means as well as by numerical model. Experimental process involves tests with various hydraulic pressures (which cause various frictional forces) at nearly static loading as well as dynamic loading with various frequencies. The results show that the proposed damper has significant energy absorption by stable hysteretic loops, which can be used for enhancement of the performance of structures subjected to earthquake loads with various intensities. Force–displacement characteristics of AFD such as slippage load, dissipated energy, effective stiffness and equivalent viscous damping for consecutive cycles of loading is calculated. The system is qualified based on the requirements for displacement-dependent devices according to ASCE/SEI 41-06 specification. Furthermore, the hysteretic behavior of AFD is studied by numerical method and a close agreement between the experimental and numerical results is observed.

The Effects of Various Slippage Loads on the Response Modification Factor of Steel Structures Equipped with Frictional Dampers

A common and successful way of structural control is to dissipate the seismic kinetic energy via frictional dampers. Response of a friction damped frame during an earthquake excitation is heavily dependent to the slippage limit of the frictional dampers. Low values of slippage load may lead to excessive deformations while large slippage loads may prevent sliding. Therefore, selecting appropriate values for slippages loads of the dampers is very important in order to have optimum energy dissipating system. Utilizing a response modification factor, the standard seismic design code procedure can be applied to the frames equipped with frictional dampers to determine the value of slippage loads. In this investigation, the response modification factor of steel moment resisting frames equipped with frictional dampers is evaluated considering the effects of various slippage loads. The response modification factor is calculated for two bay widths of 5 m and 7 m in length. It is shown that the optimum slippage load that results in the maximum response modification factor is in the range of 8% to 20% of the total weight of the structure. The taller the structure is, the less the optimum slippage load will be. Finally, an equation is proposed for the response modification factor as a function of the slippage load.

The Effects of Dynamic Loading on Hysteretic Behavior of Frictional Dampers

During an earthquake excitation, a frictional damper may experience many cycles of dynamic loading. The effects of wear and heat induced by the cyclic loading result in the possible decay of the slippage load which subsequently reduce the energy absorption of the damper. In this paper, the effect of dynamic loading on hysteretic behavior of a special kind of frictional damper, namely, cylindrical frictional damper (CFD), is investigated by experimental means as well as numerical models which also account for coupled thermal-structural interaction. The damper is deemed to be more susceptible to thermal deformations due to the shrink-fit mechanism by which the device is assembled. The numerical models are validated experimentally and may be utilized for simulation of dynamic cyclic loading on frictional dampers. The results demonstrate that the slippage load is reduced gradually when subjected to consecutive cycles. This drift is attributed to thermal deformation. The verified numerical models are used to improve the geometry of the CFD. With the geometrical improvements implemented, the subsequent numerical studies confirmed that almost no degradation of the slippage load occurred. Furthermore, a dimensionless parameter is introduced by the authors which shows the effect of wear on the response of CFDs.

Geotextile friction mobilization during field pullout test

Small-scale laboratory tests may not yield reliable values for soil–geotextile interface properties due to the effect of scaling. Field tests offer a better alternative to overcome this problem. In situ pullout tests were performed on a full-scale embankment built over a woven polyester geotextile sheet. The field tests were conducted using different fill heights of compacted clayey soil. The performance of the geotextile was examined when the base soil underneath the geotextile was stiff clay of high plasticity or compacted clean river sand. The test section was instrumented to monitor the geotextile movement and the applied pullout force. Results of the tests showed a linear increase in the geotextile frictional resistance with the increase in the fill height. Also, a successive movement response at different locations on the geotextile away from the loaded edge was detected during the early stages of loading. At the slippage load, a continuous rigid body translation occurred in the geotextile sheet without any further increase in the applied pullout force. The suitability of a widely used interface numerical model that consists of a zero-thickness joint element and a nonlinear elastic hyperbolic stress-deformation material model was examined using the finite element technique. The results showed the inadequacy of this model to deal with large deformation problems typically experienced in geosynthetic reinforced soils.