Torsional Stress - Inhomogeneous Deformation (Steel, Copper and Aluminium Alloys)

Video in TIB AV-Portal: Torsional Stress - Inhomogeneous Deformation (Steel, Copper and Aluminium Alloys)

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Torsional Stress - Inhomogeneous Deformation (Steel, Copper and Aluminium Alloys)
Alternative Title
Torsionsbeanspruchung - Inhomogenitäten bei der Verformung von Stahl, Kupfer und Aluminiumlegierungen
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E 2440
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Technical Metadata

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Film, 16 mm, LT, 119 m ; SW, 11 min

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Subject Area
Demonstration of different kinds of inhomogeneous torsional deformation caused by: local heating, orientation changes of the crystalite, dynamic strain ageing. Also: homogeneous deformation, "curling out", jerky deformation, torsional fracture.
Keywords aluminium alloys / torsional stress light metal / torsion copper / torsional stress steel / torsional stress torsion deformation / torsional deformation
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Computer animation
Cylindrical testing rod. Surface of the sample chemically etched and marked in the longitudinal direction with 4 lines displaced by 90 degrees. Steel X 8 Cr 17 rolled. Torsion of the cylindrical steel sample is just beginning. The length of the visible part of the testing length is 40 mm. The sample is being twisted at the right-hand end at a constant velocity of rotation. The left-hand sample clamp is prevented from twisting but can be axially displaced to allow for changes of sample length. All of the experiments were recorded at 24 fps (frames per second). The present deformation velocity is 1.1 %/s. The 4 lines on the sample surface displaced by 90 degree have turned into spirals during torsion. The smaller the spacing of the spiral lines, the greater is the degree of deformation. For homogeneous deformation, the spacing of any two lines is the same anywhere on the sample. To the left of frame centre, the lines are now bunching together more quickly than in other regions, the deformation process is becoming inhomogeneous. Here, in the region of maximum deformation, the sample breaks apart.
The deformation velocity is increased by a factor 9 to 10 %/s. Homogeneous deformation. Inhomogeneous deformation begins. The more strongly deformed region extends to the left and right beyond the visible part of the sample.
Every sample can only withstand a certain degree of deformation. The testing time diminishes in proportion to the increasing deformation velocity. Deformation velocity: 30 %/s. (Steel X 5 CrNiMoCu 18 18, rolled.) In this material, after the first deformation inhomogeneity, further waves of deformation occur in the same sample region. Deformation velocity 30 %/s. Deformation on the left a maximum 900 %, on the right only about 60 %. Copper E-Cu, hard-drawn. This copper sample will be subjected to a deformation of 10 %/s. The deformation will become inhomogeneous after only one second, at the left-hand edge of the frame. The differences in the degree of deformation balance out in the course of the experiment.
(40 s later.) The mean degree of deformation is now 700 %. In the fracture region the deformation is slightly stronger than at the right-hand edge of the frame.
Initially stronger deformation at the right-hand edge of the frame. The deformation velocity is 30 %/s. After a 24 s duration of the experiment (up to fracture), the mean degree of deformation is about 720 %.
This time the degree of deformation in the fracture region is markedly stronger.
At a deformation velocity of 90 %/s, the experiment time is strongly reduced. At this very high deformation velocity the deformation was concentrated much more strongly in the fracture region. Aluminium alloy AlMgSi 0.5, press-worked. Deformation velocity 30 %/s. After one second homogeneous deformation we have "curling out".
Here too: somewhat stronger deformation in the fracture zone.
The same material at 90 %/s. Degree of deformation at the
fracture site 400 % - on the left 50 %. (The same material, solution heat-treated.) By thermal post-treatment the "curling out" shown earlier is suppressed. We have apparently homogeneous deformation. On closer observation one can recognize a different kind of inhomogeneity: "jerky deformation". (Aluminium alloy AlMg 3, hard-drawn.) Deformation velocity 10 %/s. This aluminium-magnesium alloy shows jerky deformation from the start. Temporarily there are additional curling effects.
The material is approximately equally strongly deformed throughout.
Deformation velocity increased to 30 %/s. Jerky deformation. Curling out. Jerky deformation. (Aluminium alloy AlCu 3, press-worked.) Deformation velocity 10 %/s. In the aluminium-copper alloy too, we initially have jerky deformation, followed by curling from the left. Now jerky deformation dominates once more.
The sample is approximately
equally strongly deformed throughout.
Deformation velocity 30 %/s. Jerky deformation; (in addition: curling from the left.) Jerky deformation only, up to fracture. Slightly stronger deformation in the region of the fracture zone.