Search results for "Force level"
showing 9 items of 9 documents
Springback effect evaluation in three-dimensional stamping processes at the varying of blankholder force
2006
The quantitative evaluation of elastic springback in sheet metal stamping processes is still today a very interesting research topic, since this phenomenon causes a manufacturing shape defect. A measurement technique based on the shadow moiré method, already developed by the present authors, has been further upgraded and applied to evaluate the springback phenomenon in the deep drawing of square boxes, the basic three-dimensional stamping process. In particular this technique is able to determine the final lateral surface of the drawn parts, once extracted from the dies, and to compare such surface with the ideal one derived from the die's computer-aided design (CAD) geometry. Proper quant…
An Optical Technique for Springback Measurement in Axisymmetrical Deep Drawing Operations
2001
Abstract In this paper, a measurement technique based on the shadow moire method has been set up to evaluate the springback phenomenon in deep drawing operations. Two proper coefficients are introduced to quantitatively describe the investigated effect. In particular, the proposed technique is able to acquire the final profile of the drawn parts along one or more lateral contour, once extracted out from the dies, and compare such profile with the ideal one derived from the dies CAD geometry. The proposed technique has been applied to an axisymmetrical deep drawing operation, and, moreover, the influence of the blankholder force level and lubricating conditions has been taken into account. T…
Alterations of mechanical characteristics of human skeletal muscle during strength training
1983
To investigate the influence of strength training on the mechanical characteristics of human skeletal muscle, 14 male subjects went through training of combined heavy concentric and eccentric contractions three times a week for 16 weeks. The strength training program consisted mainly of dynamic exercises for leg extensors with loads of 80 to 120% of one maximum repetition. The force-time curves produced during various vertical jumps were the basis for calculation of various mechanical parameters. In addition to a great increase (p less than 0.001) in maximal isometric force, heavy resistance strength training also caused significant (p less than 0.05-0.01) increases in heights and in variou…
Maximal force, force/time and activation/coactivation characteristics of the neck muscles in extension and flexion in healthy men and women at differ…
2002
This study examined the force production characteristics, activation/coactivation and endurance capacity of the neck extension and flexion muscles in healthy men (n=29) and women (n=28) divided into three age groups (18–26 years, 30–37 years and 45–55 years). Force and electromyography (EMG) measurements were performed during the maximal voluntary isometric extension and flexion actions. This was followed by an endurance test (ET; 60% force level of maximal voluntary contraction sustained until exhaustion), after which the force and EMG recordings were repeated. Men were both stronger and had higher values (P<0.001) for explosive force (rate of force development, RFD) than women in both act…
Neuromuscular, anaerobic, and aerobic performance characteristics of elite power athletes.
1984
Various aspects of neuromuscular, anaerobic, and aerobic performance capacity were investigated in four powerlifters, seven bodybuilders, and three wrestlers with a history of specific training for several years. The data (means +/- SD) showed that the three subject groups possessed similar values for maximal isometric force per unit bodyweight (50.7 +/- 9.6, 49.3 +/- 4.1, and 49.3 +/- 10.9 N/kg, respectively). However, significant (P less than 0.05) differences were observed in the times for isometric force production, so that e.g., times to produce a 30% force level were shorter for the wrestlers and bodybuilders (28.3 +/- 3.1 and 26.4 +/- 6.6 ms) than that (53.3 +/- 23.7 ms) for the powe…
Neuromuscular control in landing from supra-maximal dropping height.
2009
International audience; The present study utilized high-impact supra-maximal landings to examine the influence of the pre-impact force level on the post-impact electromyographic (EMG) activity and, in particular, on the short latency EMG reflex (SLR) component. Unilateral-leg landings were performed in a sitting position on a sledge apparatus after release from high, but individually constant dropping height. A lower limb guiding device fixed to the front of the sledge seat allowed the subjects to sustain a given pre-set force level up to impact. This force level was either freely chosen or set at 20, 35, and 50% of maximal isometric plantarflexion force. EMG activity was recorded from eigh…
Springback Evaluation In Basic Sheet Metal Stamping Processes
2000
In the present paper a measurement technique based on the shadow moire method has been set up in order to evaluate the springback phenomenon in deep drawing operations. Two proper coefficients are introduced to quantitatively describe the effect considered. In particular the proposed technique is able to acquire the final profile of the drawn parts along one or more generatrices, once extracted out from the dies and to compare such profile with the ideal one derived from the dies CAD geometry. The proposed technique has been applied to an axysimmetrical deep drawing operation and moreover the influence of the blankholder force level and of the lubricating conditions have been taken into acc…
Effects of fatigue and recovery on electromyographic and isometric force- and relaxation-time characteristics of human skeletal muscle
1986
Effects of fatigue produced by a maintained 60% isometric loading on electromyographic and isometric force-time and relaxation-time characteristics of human skeletal muscle were studied in 21 males accustomed to strength training. Fatigue loading resulted in a slight but not significant change in the maximal integrated EMG of a maximal isometric contraction, and a large decrease (20.4 +/- 6.3%, p less than 0.001) in maximal force. Fatigue loading increased (p less than 0.05-0.01) neural activation of the muscles during rapidly produced submaximal isometric forces, but had a considerable adverse effect (p less than 0.001) on the corresponding force-time characteristics. Correlations between …
Performance‐determining factors in biathlon prone shooting without physical stress
2021
This study investigated the most important factors determining biathlon prone shooting performance. 10 female and 16 male biathletes (age 19.9 ± 2.9 years) from the national teams of Finland and Vuokatti-Ruka Sports Academy performed 65 biathlon prone shooting shots without physical stress under laboratory conditions. Shooting performance and multiple aiming point trajectory variables were measured together with an analysis of triggering force. Based on the aiming point trajectory data principal component analysis, we identified four technical components in biathlon prone shooting: stability of hold, aiming accuracy, cleanness of triggering and timing of triggering. Multiple regression anal…