![]() In fact, when Yale won 8-0, it finished its whole season completely unscored upon. 20, between two undefeateds - Yale and Harvard - was typical of the era. In the season's championship match - what may be called the first "game of the century" - The New York Times summed it up as "an indescribable tangle of bodies, arms and legs." However, by ought-nine, as they said back then, it was still a brutal battle royal. This month is the centennial of what has all but been forgotten - a moment that could have ended football in America but instead forced the sport down a different, better path.įootball was so gruesome at the turn of the century that in 1905, no less than President Roosevelt himself demanded that the sport clean itself up, and the notorious flying wedge was banned. Before ESPN: Football has always been a contact sport - even in the 1930s, when this photo of players for Boston and Geneva College was taken. The deformation of the specimen in terms of the current minimum diameter was measured during the test. ![]() During each test on the flying wedge, the impacting wedge velocity was measured to a res- olution of 0.01 m/s just before impact using a photographic fringe technique. The 28 ◦ wedge-slider combination was used in the present work with different wedge velocities to achieve a relatively narrow range of high strain rates (300–1000 s − 1 ). ![]() By varying the speed of the impacting wedge (3–9 m s − 1 is a typical range) and wedge semi-angles (5 ◦, 28 ◦ and 45 ◦ semi-angled components are available), a wide range of strain rates (10 2 –10 4 s − 1 ) can be achieved. It is based on the simple idea of holding a tensile specimen between a pair of sliders with chamfered faces which are impacted upon by a wedge of matching semi-angles fired from a gas gun at high velocity, thereby subjecting the specimen to high speed uniaxial tension simultaneously from both ends (Sturges and Cole, 2001). The high strain rate tests were performed on the so-called ‘flying wedge’ dynamic tensile testing machine, Figure 3, which is capable of imparting simultaneous symmetrical loading at both ends of a tensile specimen over a wide range of loading speeds. This assumption was reasonable because the specimens showed no sign of incipient necking up until fracture. This change in gauge length and the corresponding load were then used to plot the true stress-true strain curve of the UHMWPE making the usual assumption of constant volume during plastic deformation. From these measurements, the change in gauge length of the specimen was obtained at each time increment using the Dartec analysis software. ![]() The load was read directly from the load digital display associated with the machine and the elongation of the axisymmetric specimen was measured using the stationary laser extensometer (Elsayed, 2000). The load and the corresponding elongation were recorded simultaneously at certain increments of cross-head displacement. quasi-static tests were conducted on a Dartec standard servo-hydraulic machine equipped with a laser extensometer, Figure 2. The dynamic tests (300–1000 s − 1 ) were conducted using a unique impact tensile test facility known as the ‘flying wedge’, Figure 3, which is capable of applying strain rates in the range 10 2 up to 10 4 s − 1 (Sturges and Cole. The quasi-static tests (0.005–0.05 s − 1 ) were carried out using a Dartec servo-hydraulic universal testing machine (Elsayed, 2000), Figure 2. The strain rate was varied by carrying out tensile tests at both quasi-static and dynamic rates, ranging from 0.005 up to 1000 s − 1. To obtain a range of stress triaxiality factor (defined as the ratio of the mean stress σ m to the von Mises effective stress σ e ), notches of different notch profile radius (4, 2, 1, and 0.5 mm) were machined in the plain cylindrical tensile specimens as shown in Figure 1b. 0 × 10 6 g mol − 1 and 936 kg m − 3, respectively (Kurtz et al., 1998). ![]() The reported average molecular weight and density for the UHMWPE used in this study are 2.0 to 4. The polymer sheet was compression molded by Poly Hi Solidur Meditech (Germany) from UHMWPE powder provided by Hoechst AG (Germany). specimens were machined from rectangular compression molded sheet of UHMWPE type GUR1120 to give a cylindrical cross-section of 3 mm diameter and 15 mm gauge length as shown in Figure 1a. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |