Sudden Load Decrease Research Articles

Analysis of debonding mechanism and concrete cover failure of steel and steel fibre reinforced concrete composite beams

To solve the construction problems of steel reinforced concrete structures, the rebar cage was replaced by steel fibres, thus an innovative structure, steel and steel fibre reinforced concrete (SSFRC) structure, was proposed. Based on the four-point bending tests and numerical modelling of 18 SSFRC beams, the debonding mechanism and concrete cover failure were investigated. The results reflected that SSFRC beams experienced shearing failure, debonding failure and bending failure. Bonding cracks existed in most specimens, and the generation of abundant bonding cracks led to the sudden load decrease. The uncoordinated deformation between concrete cover and top flange appeared during the internal force transmission, making the bonding interface between them resist strong tensile stress and resulting in the debonding failure. After the chemical bond force at the bonding interface failed, the lateral concrete cover was firstly torn at the top flange tip, forming bonding cracks. The trapezoidal failure zone would form in the pure bending zone if bonding cracks developed sufficiently. Increasing the amount of steel fibres could prevent the trapezoidal failure zone from separation. Influenced by debonding failure, the extrusion action between bottom flange and bottom concrete cover was aggravated, generating longitudinal splitting cracks on the bottom surface of specimen.

Effect of Poly-L-Lactic Acid Mesh Augmentation on Cyclic Gap Formation in Transosseous Patellar Tendon Repair: A Biomechanical Study.

No previous study has investigated poly-L-lactic acid (PLLA) surgical mesh augmentation in the repair of inferior pole patellar tendon rupture. We compared the biomechanical properties of transosseous patellar tendon repair with PLLA surgical mesh augmentation to transosseous repair without augmentation. Ten matched pairs of cadaveric knees were used. Specimens in each pair were randomized to undergo the transosseous technique alone or the transosseous technique augmented with a PLLA surgical mesh. An inferior pole patellar tendon rupture was simulated and the repair procedure was performed. Specimens were cyclically loaded for 500 cycles. Gap formation was measured using two sensors placed medial and lateral to the repair site. After cyclic loading, load to failure was determined by pulling the tendon at a constant rate until a sudden decrease in load occurred. The primary outcome measure was cyclic gap formation at the medial and lateral sensors. Compared with controls, specimens that underwent PLLA mesh-augmented repair had significantly lower medial gap formation at all testing intervals up to 500 cycles (p < 0.05) and significantly lower lateral gap formation at all testing intervals from 10 to 500 cycles (p < 0.05). Transosseous patellar tendon repair augmented with a PLLA woven mesh device provided significantly greater resistance to gap formation compared with transosseous repair alone. These results suggest that PLLA mesh augmentation of the transosseous technique is biomechanically effective for patellar tendon repair.

Implementation of protection circuit for over voltage and under voltage protection

This paper identifies the development of an under voltage and over voltage protection in order to avoid damage in load side. Most of the industries and as well as home appliances are very expensive also more sensitive. This may get damaged due to the instabilities in ac mains supply. It can also lead to losses in the electrical circuit. These losses lead to low power factors and wastage of so much power. The fluctuations can cause great impact to the power quality and many precious and expensive equipment may be damaged. It is therefore advisable to have a tripping mechanism to protect the load. The voltage below the rated value are usually caused under unexpected raise in load due to faults in the system, during short circuit conditions and also rapid increase in source impedance due to lose connection in the circuit. The voltage above the rated values are caused by a sudden decrease in load in a circuit having a poor or damaged voltage regulator. The over voltage may also be caused by a damage in the circuit or loose connections in neutral wire. In this paper, the solution to under voltage and over voltage conditions has been carried out. The proposed circuit will be able to work within the voltage ratings of 195–215 V. Anything below that will be considered as under voltage and anything above that will be considered as over voltage. Thus, we can protect the equipment from damage. By doing this, the proposed circuit is able to protect the electrical appliance. The promising results obtained are presented and discussed here.

High-Strength Suture Tape Augmentation Improves Cyclic Gap Formation in Transosseous Patellar Tendon Repair: A Biomechanical Study

PurposeTo compare gap displacement at various intervals of cyclic testing and biomechanical load to failure of a Krackow patellar tendon repair augmented with high-strength suture tape versus the standard Krackow transosseous technique for inferior pole patellar tendon rupture.MethodsTwelve matched pairs of cadaveric knees were used (8 males and 4 females; mean age 79.6 years, range 57 to 96). An inferior pole patellar tendon rupture was simulated after random assignment of specimens in each pair to the standard or augmented Krackow technique. Each specimen was then repetitively cycled from 90° to 5° for 1,000 cycles. A differential variable reluctance transducer was used to measure gap displacement. After cyclic loading, load to failure was determined by pulling the tendon at a rate of 15 mm/s until a sudden decrease in load occurred.ResultsCompared with the control repair, specimens with augmented repair demonstrated significantly less displacement at all testing intervals up to 1,000 cycles (P < .05). Two patellar tendons failed before the end of cyclic loading, and 4 specimens had inadequate tendon length for loading. Among the 18 remaining specimens, no significant difference in load to failure was observed between the experimental group (n = 11) and the control group (n = 7) (1,006.5 ± 332.1 versus 932.8 ± 229.1 N, respectively; P = .567).ConclusionsSignificantly greater gap displacement was observed in the standard Krackow repair group compared with the augmented Krackow group at all cyclic loading intervals. This suggests that the Krackow transosseous procedure augmented with high-strength suture tape is biomechanically viable for inferior pole patellar tendon repair.Clinical RelevanceThis biomechanical study supports the use of high-strength suture tape augmentation of Krackow transosseous repair for inferior pole patellar tendon rupture.

Stability analysis of nonlinear hydroelectric power generating system in the transition of sudden load decrease

ABSTRACT This article presents the modeling and the dynamical behavior of a nonlinear hydroelectric power generating system with surge tank effects and its stability in the case of sudden load decrease. A novel seven-dimensional nonlinear model of the complex hydroelectric power generating system with surge tank effects is proposed. Six nonlinear partial derivative coefficients of sudden load decrease are introduced into the generating system. The numerical results are analyzed by the Adams-Bashforth-Moulton algorithm, and the nonlinear dynamic characteristics of the system variables and PID governor parameters are investigated, particularly using characteristic diagrams to discuss the stability of the nonlinear system from the viewpoint of engineering. Involving the surge tank effects, the generating system keeps steady when the range of the governor parameter is less than 7.9 s. The increment of the governor parameter can extend stability regions of the governor parameter . In addition, the system remains unsteady when the engager relay time constant is less than 0.1 s, but when it is more than 0.1 s, the system sustains a steady state. Finally, the analytical results provide principal references for studying and operating hydroelectric power stations during sudden load decrease.

Impact of machine stiffness on ‘‘pop-in’’ crack propagation instabilities

This study investigates ‘‘pop-in’’ phenomenon, i.e. unstable but limited crack propagation associated with a sudden decrease in load. Its origin is linked to an interaction between material tearing modulus and machine stiffness. Small scale yielding criterion for instability is applied to compact tension (CT) samples. To validate this criterion experimentally, firstly tests are performed on aluminum alloy with various tearing moduli. Secondly the effect of mechanical loading on pop-in behavior is studied by varying machine stiffness using an innovative setup. Pop-ins are shown to be mechanical instabilities due to interaction between material tearing modulus and system stiffness.

Dynamic analysis of multi-unit hydropower systems in transient process

This paper addresses a mathematical model and dynamic analysis of multi-unit hydropower systems in transient process. In this work, the first unit is assumed to be subject to a sudden load decrease, while the second unit runs with load. An approach to the description of the six stochastic dynamic transfer coefficients of the hydro-turbine is proposed for the second unit. Moreover, a novel dynamic model for the multi-unit hydropower system, able to take into account the eventual occurrence of water hammer in the penstock and the nonlinearity of the generator, is introduced. Also, a numerical application is analyzed in order to investigate the effectiveness of the approach proposed and the dynamic characteristics of the system under study. Finally, a comparative analysis is proposed in order to validate the proposed system. The methods and results implemented in this work provide theoretical tools to guarantee the stable operation of hydropower stations.

Effect of sudden load decrease on the fatigue crack growth in cold drawn prestressing steel

This paper analyzes the overload retardation effect (ORE) on the fatigue crack growth (FCG) of cold drawn prestressing steel when different loading sequences are used. The ORE is more intense for elevated load decrease or for low initial stress intensity factor (SIF) range ΔK0. A transient stage can be observed in the Paris curve (da/dN–ΔK) when the KmaxΔK value suddenly decreases, associated with the ORE and with the evolution of the plastic zone and compressive residual stresses near the crack tip. In tests with Kmax decrease, a small zone appears related to FCG initiation, with a fatigue fractography resembling the tearing topography surface (TTS) mode, and associated with a decrease of crack tip opening displacement (CTOD).

Elastohydrodynamic lubrication analysis of hip implants with ultra high molecular weight polyethylene cups under transient conditions

The transient variation of both the load and speed experienced during walking in an elastohydrodynamic lubrication (EHL) analysis for artificial hip joints employing an ultra high molecular weight polyethylene (UHMWPE) acetabular cup against either a metallic or ceramic femoral head was considered in this study. A general numerical procedure to solve the transient EHL problem in spherical ball-in-socket coordinates, developed in a previous study by Jalali-Vahid and Jin in 2002, was applied under three specific conditions experienced during typical gait cycles, including speed reversal, a sudden load increase and a sudden load decrease. The predicted minimum film thickness was found to stay remarkably constant and similar to that prior to the change in either the load or the angular velocity, despite a large change in these operating conditions. This was attributed to the remarkably effective squeeze-film action of preserving and maintaining the lubricating film developed before the transient variations in either the load or speed. It is therefore possible to neglect the effect of these specific transient variations of load and speed under physiological walking conditions considered in the present study on the predicted film thickness in hip implants with UHMWPE cups.

Muscle spindle responses in man to changes in load during accurate position maintenance.

1. Single unit and multi-unit recordings of muscle spindle activity were made from the peroneal nerves of human subjects. While the subjects attempted to maintain a constant ankle joint position, an external load on the receptor-bearing muscle was altered unexpectedly. 2. The spindle discharge produced by a sudden increase in load was of similar strength when the receptor-bearing muscle was relaxed as when it was contracting at the moment of the impact. A motor response at a latency consistent with a spinal reflex mechanism occurred only when the muscle was contracting. It is concluded that the potentiation of the reflex mechanism during contraction was not due primarily to a fusimotor action. 3. Sudden decrease in load produced a pause in spindle discharge followed by a pause in on-going e.m.g. activity at a latency consistent with spinal reflex mechanisms. 4. Slow changes in load produced parallel changes in e.m.g. and spindle discharge. It is suggested that the voluntary effort involved in maintaining joint position in the face of gradually changing loads results in corticospinal activity adjusted in strength to the opposing torque and operating on alpha and gamma motoneurones in parallel.