Torsion testing

Rotation resistance tests are conducted on mechanical saddles to meet the requirements of ASTM F 1924 section 6.2.2.3. Tests are conducted on six of the smallest size and six of the largest nominal pipe sizes. Rotation Test Torsion Load Requirements are 30 ft-lbf for 1 14 TPS and 50 ft-lbf for 2 IPS and larger saddles. The fittings are leak tested following torsion. Our experience has been that mechanical saddles for larger diameter pipe require higher torque loads to eause rotation. Sixty-six fittings have passed the rotation resistance test. 

Mixtures containing up to several thousand distinct chemical entities are often synthesized and tested in mix-and-split combinatorial chemistry. The descriptor representation of a mixture may be approximated as the descriptor average of its individual component molecules, e.g., using atom-pair and topological torsion descriptors. 

Although a torsion test is simple to carry out, it is not commonly accepted as an integral part of a material specification furthermore, few torsion data exist in handbooks. If, as is usually the case, the design needs to be based on tensile data, then a criterion of elastic failure has to be invoked, and this introduces some uncertainty in the calculated yield pressure (8). 

Plots of the bursting pressures of the Ni—Cr—Mo cylinders (EN 25) vs k derived from equations 16 and 17 show that neither equation is in such good agreement with the experimental results as is the curve derived from Manning s theory. Similar conclusions have been reached for cylinders made of other materials which have been tested (16). Manning s analytical procedure may be programmed for computation and, although torsion tests are not as commonly specified as tension tests, they are not difficult or expensive to carry out (20). 

Rheometric Scientific markets several devices designed for characterizing viscoelastic fluids. These instmments measure the response of a Hquid to sinusoidal oscillatory motion to determine dynamic viscosity as well as storage and loss moduH. The Rheometric Scientific line includes a fluids spectrometer (RFS-II), a dynamic spectrometer (RDS-7700 series II), and a mechanical spectrometer (RMS-800). The fluids spectrometer is designed for fairly low viscosity materials. The dynamic spectrometer can be used to test soHds, melts, and Hquids at frequencies from 10 to 500 rad/s and as a function of strain ampHtude and temperature. It is a stripped down version of the extremely versatile mechanical spectrometer, which is both a dynamic viscometer and a dynamic mechanical testing device. The RMS-800 can carry out measurements under rotational shear, oscillatory shear, torsional motion, and tension compression, as well as normal stress measurements. Step strain, creep, and creep recovery modes are also available. It is used on a wide range of materials, including adhesives, pastes, mbber, and plastics. 

Acceptable comprehensive methods of analysis are analytical, model-test, and chart methods, which evaluate for the entire piping system under consideration the forces, moments, and stresses caused by bending and torsion from a simultaneous consideration of terminal and intermediate restraints to thermal expansion and include all external movements transmitted under thermal change to the piping by its terminal and intermediate attachments. Correction factors, as provided by the details of these rules, must be applied for the stress intensification of curved pipe and branch connections and may be applied for the increased flexibihty of such component parts. 

Torsional test and minimum torques for bolts and screws with nominal diameters I mm to lO mm Specification for spring washers for general engineering and automobile purpo.ses, Metric series Code of practice for design of high-voltage open-terminal stations... 

The torsional resonant response of a system is an interaction of all the components in the train. Calculation of torsional natural frequencies is based on the entire system and these frequencies are valid only for that given arrangement. If any component of the train is replaced by an item with torsional characteristics different from the original, the system tor sional response must be recalculated and new torsional natural frequencies determined. Occasionally, an original equipment manufacturer is requested to calculate the torsional and lateral critical speeds of the supplied item. Unfortunately, the purchaser is unaware that this request is of limited value since the torsional response of a single item in a train is meaningless. Likewise, a torsional shop test will yield meaningless results if the train is not assembled and tested with every item destined for the field. 

Type of stress. A uniaxial tensile creep test would not be expected to give the required data if the designer was concerned with torsional or compressive creep. 

The torsion-tube test described by Whitney, Pagano, and Pipes [2-14] involves a thin circular tube subjected to a torque, T, at the ends as in Figure 2-29. The tube is made of multiple laminae with their fiber directions aligned either all parallel to the tube axis or all circumferentially. Reasonable assurance of a constant stress state through the tube thickness exists if the tube is only a few laminae thick. However, then serious end-grip difficulties can arise because of the flimsy nature of the tube. Usually, the thickness of the tube ends must be built up by bonding on additional layers to introduce the load so that failure occurs in the central uniformly stressed portion of the tube (recall the test specimen criteria). Torsion tubes are expensive to fabricate and require relatively sophisticated instrumentation. If the shearing strain y 2 is measured under shear stress t.,2, then... 

The hydrogen treatment procedures, tensile, compression and torsion tests at fixed temperatures, transmission electron or optical microscopy at room temperature as well as X-ray diffraction measurements were detailed elsewhere All experiments were performed so as to compare properties of the same alloy, but modified using different treatment procedures. 

Figure 5. Ductility (ultimate angle strain) of the Ti-6Al-2Zr-1.5V-lMo-xH alloys in dependence on the strain rate in torsion tests at 607° - 1, 660° - 2, 720° - S and 780°C - 4.

Wire used in the manufacture of wire rope is made from (1) acid or basic open-hearth steel, (2) basic oxygen steel, or (3) electric furnace steel. Wire tested before and after fabrication shall meet different tensile and torsional requirements as specified in Tables 4-9 and 4-10. 

During the torsion test, tension weights as shown in Table 4-13 shall be applied to the wire tested. 

The minimum torsions for individual bright (uncoated) or drawn-galvanized wire of the grades and sizes shown in Columns 7, 12, and 17 of Tables 4-9 and 4-10 shall be the number of 360° (6.28 rad) twists in an 8-in. (203 mm) length that the wire must withstand before breakage occurs. Torsion tests of individual wires in galvanized wire rope and of individual wires in strand cores and independent wire rope cores are not required. 

When the distance between the jaws of the testing machine is less than 8 in. (203 mm), the minimum torsions shall be reduced in direct proportion to the change in jaw spacing, or determined by... 

The remaining section of the 3-ft (0.91-m) test specimen shall be gaged for size and tested for torsional requirements. 

It has also been shown by various testing laboratories that the in-vivo failures can be simulated using in-vitro simulators without the presence of a corrosive medium and provided that a torsional component of load is applied to the prosthesis. 

There are several other comparable rheological experimental methods involving linear viscoelastic behavior. Among them are creep tests (constant stress), dynamic mechanical fatigue tests (forced periodic oscillation), and torsion pendulum tests (free oscillation). Viscoelastic data obtained from any of these techniques must be consistent data from the others. 

The shear modulus of a material can be determined by a static torsion test or by a dynamic test employing a torsional pendulum or an oscillatory rheometer. The maximum short-term shear stress (strength) of a material can also be determined from a punch shear test. 

Because strain measurements are difficult if not impossible to measure, few values of yield strength can be determined by testing. It is interesting to note that tests of bolts and rivets have shown that their strength in double shear can at times be as much as 20% below that for single shear. The values for the shear yield point (kPa or psi) are generally not available however, the values that are listed are usually obtained by the torsional testing of round test specimens. 

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