Application of bending under tension test to determine the effect of tool radius and the contact pressure on the coefficient of friction in sheet metal forming

To quantify the frictional behaviour in sheet forming operations, several laboratory experiments which simulate the real forming conditions are performed. The Bending Under Tension Test is one such experiment which is often used to represent the frictional flow of sheet material around a die or a punch radius. Different mathematical representations are used to determine the coefficient of friction in the Bending Under Tension Test. In general the change in the strip thickness in passing over the die radius is neglected and the radius of curvature to thickness ratio is assumed to be constant in these equations. However, the effect of roller radius, sheet thickness and the surface pressure are also omitted in some of these equations. This work quantitatively determined the effect of roller radius and the tooling pressure on the coefficient of friction. The Bending Under Tension Test was performed using rollers with different radii and also lubricants with different properties. The tool radii were found to have a direct influence in the contact pressure. The effect of roller radius on friction was considerable and it was observed that there is a clear relationship between the contact pressure and the coefficient of friction.

Ice and pulsed electromagnetic field to reduce pain and swelling after distal radius fractures

Objective: To examine the relative effectiveness of ice therapy and/or pulsed electromagnetic field in reducing pain and swelling after the immobilization period following a distal radius fracture.Methods: A total of 83 subjects were randomly allocated to receive 30 minutes of either ice plus pulsed electromagnetic field (group A); ice plus sham pulsed electromagnetic field (group B); pulsed electromagnetic field alone (group C), or sham pulsed electromagnetic field treatment for 5 consecutive days (group D). All subjects received a standard home exercise programme. A visual analogue scale was used for recording pain; volumetric displacement for measuring the swelling of the forearm; and a hand-held goniometer for measuring the range of wrist motions before treatment on days 1, 3 and 5.Results: At day 5, a significantly greater cumulative reduction in the visual analogue scores as well as ulnar deviation range of motion was found in group A than the other 3 groups. For volumetric measurement and pronation, participants in group A performed better than subjects in group D but not those in group B.Conclusion: The addition of pulsed electromagnetic field to ice therapy produces better overall treatment outcomes than ice alone, or pulsed electromagnetic field alone in pain reduction and range of joint motion in ulnar deviation and flexion for a distal radius fracture after an immobilization period of 6 weeks.

Short-term and long-term site-specific effects of tennis playing on trabecular and cortical bone at the distal radius

Mechanical loading during growth magnifies the normal increase in bone diameter occurring in long bone shafts, but the response to loading in long bone ends remains unclear. The aim of the study was to investigate the effects of tennis playing during growth at the distal radius, comparing the bone response at trabecular and cortical skeletal sites. The influence of training duration was examined by studying bone response in short-term (children) and long-term (young adults) perspectives. Bone area, bone mineral content (BMC), and bone mineral density (BMD) of the radius were measured by DXA in 28 young (11.6 ± 1.4 years old) and 47 adult tennis players (22.3 ± 2.7 years old), and 70 age-matched controls (12 children, 58 adults) at three sites: the ultradistal region (trabecular), the mid-distal region, and the third-distal region (cortical). At the ultradistal radius, young and adult tennis players displayed similar side-to-side differences, the asymmetry in BMC reaching 16.3% and 13.8%, respectively (P < 0.0001). At the mid- and third-distal radius, the asymmetry was much greater in adults than in children (P < 0.0001) for all the bone parameters (mid-distal radius, +6.6% versus +15.6%; third-distal radius, +6.9% versus +13.3%, for BMC). Epiphyseal bone enduring longitudinal growth showed a great capacity to respond to mechanical loading in children. Prolonging tennis playing into adulthood was associated with further increase in bone mineralization at diaphyseal skeletal sites. These findings illustrate the benefits of practicing impact-loading sports during growth and maintaining physical activity into adulthood to enhance bone mass accrual and prevent fractures later in life.

Contact pressure evolution at the die radius in sheet metal stamping

The contact conditions at the die radius are of primary importance to the wear response for many sheet metal forming processes. In particular, a detailed understanding of the contact pressure at the wearing interface is essential for the application of representative wear tests, the use of wear resistant materials and coatings, the development of suitable wear models, and for the ultimate goal of predicting tool life. However, there is a lack of information concerning the time-dependant nature of the contact pressure response in sheet metal stamping. This work provides a qualitative description of the evolution and distribution of contact pressure at the die radius for a typical channel forming process. Through an analysis of the deformation conditions, contact phenomena and underlying mechanics, it was identified that three distinct phases exist. Significantly, the initial and intermediate stages resulted in severe and localised contact conditions, with contact pressures significantly greater than the blank material yield strength. The final phase corresponds to a larger contact area, with steady and smaller contact pressures. The proposed contact pressure behaviour was compared to other results available in the literature and also discussed with respect to tool wear.

Comparison of pQCT parameters between ulna and radius in retired elite gymnasts : the skeletal benefits associated with long-term gymnastics are bone- and site-specific

Objectives: To compare the skeletal benefits associated with gymnastics between ulna and radius.
Methods: 19 retired artistic gymnasts, aged 18-36 years, were compared to 24 sedentary women. Bone mineral content (BMC), total and cortical bone area (ToA, CoA), trabecular and cortical volumetric density (TrD, CoD) and cortical thickness (CoTh) were measured by pQCT at the 4% and 66% forearm.
Results: At the 4% site, BMC and ToA were more than twice greater at the radius than ulna whereas at the 66% site, BMC, ToA, CoA, CoTh and SSIpol were 20 to 51% greater at the ulna than radius in both groups (p<0.0001). At the 4% site, the skeletal benefits in BMC of the retired gymnasts over the non-gymnasts were 1.9 times greater at the radius than ulna (p<0.001), with enlarged bone size at the distal radius only. In contrast, the skeletal benefits at the 66% site were twice greater at the ulna than radius for BMC and CoA (p<0.01).
Conclusion: Whereas the skeletal benefits associated with long-term gymnastics were greater at the radius than ulna in the distal forearm, the reverse was found in the proximal forearm, suggesting both bones should be analysed when investigating forearm strength.

Inter-observer variation in the diagnosis of coronal articular fracture lines in the lunate facet of the distal radius

Background: Several studies support the use of CT for diagnosing coronal fractures of the distal radius but the inter-observer reliability of these observations is less well studied. We tested the null hypothesis that radiographs alone and the combination of radiographs and two-dimensional computed tomography scans (2DCT) have the same inter-observer variation for the diagnosis of coronal articular fracture lines in the distal radius. Methods: Using a web-based survey, 63 surgeons were randomized to evaluate 16 fractures of the distal radius on radiographs alone or radiographs and 2DCT for the presence or absence of a coronal fracture line of the lunate facet and, if present, the stability of the fracture. The kappa multirater measure was calculated to estimate agreement between observers. Results: The inter-observer variation in diagnosis of a coronal fracture line was fair with both radiographs and 2DCT, as was the diagnosis of instability of the volar lunate facet fracture when present. Conclusion: Two-dimensional computed tomography does not improve observer agreement on the diagnosis of coronal plane articular fracture lines in the lunate facet of the distal radius. © 2012 American Association for Hand Surgery.

The effective radius and resistance to slippage

This work reveals that parallel gripper flat-jaw configuration affects grasping effectiveness. An important finding is the fact that object grasp reliability is influenced significantly by gripper's ability to develop high resistance to object rotation in the gripper. The concept of effective torque radius, which increases resistance to object rotation in the gripper, is presented here and can be extrapolated to other grasping devices and grasping strategies to improve their reliability and make them more effective. Grippers with full-jaw contact surface and those with discrete contact areas have been investigated using simple experimental setups. Essential mathematical models needed for analytical investigation, based on simple mechanics for full-jaw contact surfaces and discrete-jaw contact surfaces, are presented. These may be useful for gripper jaw design purposes.

Defining marine important bird areas: testing the foraging radius approach

Recent international initiatives have promoted a number of different approaches to identify marine Important Bird and biodiversity Areas (IBAs), which are important areas for foraging, migrating or over-wintering seabirds. The 'Foraging Radius Approach' is one of these and uses known foraging range and habitat preferences to predict the size and location of foraging areas around breeding colonies. Here we assess the performance of the Foraging Radius Approach using GPS tracking data from six seabird species with a variety of foraging modes. For each species we compared the population home-range areas of our six study species with the home-range areas defined using the Foraging Radius Approach. We also assessed whether basic information on depth preferences from tracking data could improve these home-range area estimates. Foraging Radius Approach home-range areas based on maximum foraging radii encompassed the entire population home-range of five out of six of our study species but overestimated the size of the population home-range area in every case. The mean maximum foraging radius overestimated the population home-range areas by a factor of 4-14 for five of the six species whilst the mean foraging radius overestimated the population home-range area for half of the species and underestimated for the rest. In the absence of other data, the Foraging Radius Approach appears to provide a reasonable basis for preliminary marine IBA identification. We suggest that using the mean value of all previously reported maximum foraging radii, informed by basic depth preferences provides the most appropriate prediction, balancing the needs of seabirds with efficient use of marine space.