Tensile testing capability

Physical characterization of polymers is a common activity that research and development technologists at the Dow Chemical Company perform. A material property evaluation that is critical for most polymer systems is a tensile test. Many instruments such as an Instron test frame can perform a tensile test and, by using specialized software, can acquire and process data. Use of an extensometer eliminates calibration errors and allows the console to display strain and deformation in engineering units. Some common results from a tensile test are modulus, percent elongation, stress at break, and strain at yield. These data are then used to better understand the capabilities of the polymer system and in what end-use applications it may be used. 

The TS of the compacted samples was determined by transverse compression with a custom-built tensile tester. Tensile failure was observed for all the rectangular compacts when compressed between flat-faced platens at a speed ranging between 0.006 and 0.016 mm/sec. Platen speed was adjusted between materials to maintain a time constant of 15 2 seconds to account for viscoelastic differences the constant is the time between the sample break point and when the measured force equals Fbreak/e in the force versus time profile, where the denominator is the mathematical e. Specially modified punch and die sets permitted the formation of square compacts with a centrally located hole (0.11 cm diameter) that acted as a stress concentrator during tensile testing. This capability permitted the determination of a compromised compact TS and thus facilitated an assessment of the defect sensitivity of each compacted material. At least two replicate determinations were performed for each mechanical testing procedure and mean values are reported. 

The aim of this work is to provide both experimental information and a corresponding formalization in order to elucidate structural propellant grain safety during ignition. The experimental data were obtained from uniaxial tensile tests and simple shear tests performed with an imposed hydrostatic pressure varying from atmospheric pressure to 15 MPa. It is well established that the materials studied exhibit time-temperature and pressure-sensitive properties. The ultimate properties reported here are formalized in a proposed stress-failure criterion capable of including the pressure effect. 

Tensile tests on different polymer blends employ specimens of different sizes. To conduct a tensile test, a specimen capable of being gripped at both ends is required. The basic types of dumbbell configurations and dimensions recommended by ISO are illustrated in Eigure... 

In its present state of development, the VideoTraction system is capable of controlling a tensile test with full analysis of at least 50 images per second. The final precision is about 2% on axial stress, 0.5% on volume strain, and 0.1 % on axial strain (16). Tests can be run at any temperature compatible with dot painting resistance and thermal radiation perturbations (typically up to about 250°C). 

When the blends are subjected to tensile testing, a certain fraction of the overall strain is accommodated by conservative deformation of the material. In the PP matrix, deformation results from the combination of amorphous phase hyperelasticity and crystal plasticity, as discussed earlier (50). The PA6 phase is also capable of deforming plastically, but its flow stress in the plastic stage is much higher than that of PP. Consequently, in the PP/PA6 blends the isolated PA6 particles exhibit less... 

Tensile tests of extremely fine wires can be successfully performed in the temperature range of 4.2° to 300°K using the basic apparatus previously developed [ ], a new modification of a universal type of test chamber, and specially developed gripping techniques. If fine wires were the only type of specimen of interest or a large volume of these tests was anticipated, it would appear desirable to construct a similar, but smaller, test chamber to minimize liquid-helium consumption. The particular cryostat used in this investigation is of a universal type and is capable of accommodating various types of mechanical tests. By inserting appropriate fixtures between the pull rods, it is possible to perform compression, bend, and tensile tests of specimens of assorted sizes and shapes. 

The most important goal for each NASA-developed CMC system was to be able to operate under potential component stress levels for long time at its selected upper use temperature (UUT). To evaluate this capability, tensile test specimens from the various CMC panels were subject to creep-rupture testing in ambient air at their goal UUT and at stresses of -60% of their room-temperature cracking stress. The primary performance objective was to demonstrate greater than 500-hour life without specimen rupture. Since high-temperature mpture of an initially uncracked CMC is typically controlled by CMC... 

Tensile tests on different polymer blends employ specimens of different sizes. To conduct a tensile test, a specimen capable of being gripped at both ends is required. The basic types of dumbbell configurations and dimensions recommended by ISO are illustrated in Fig. 10.2. The American specifications differ only in number of dimensional details and are based essentially on imperial units. In case of rigid polymer blends (such as engineering blends), the specimen can be molded, machined on a lathe, or simply cut out from thin, flat sheets. 

Other tensile cryostats have been reported in the literature. Wessel [6] has described a cryostat for use with standard tensile machines that is capable of withstanding forces of up to 20,000 lb and which uses about 2 liters of liquid helium and 25--30 liters of liquid nitrogen to perform a tensile test at 4.2 K, This cryostat uses an external source of refrigeration to obtain temperatures other than those of the boiling points of the common liquefied gases and its insulating vacuum spaces were continuously evacuated during the experiment. 

Recognizing the importance of the true stress-strain test and the need for specimen diameter measurements during tests where the material deforms by a series of discontinuous yields, the Watertown Arsenal Laboratories contracted with A, D. Little, Inc. [1] to construct a tensile test cryostat capable of measuring and recording instantaneous diameter data to be compatible with an existing true-stress true-strain computer [2]. 

Tensile strength is the maximum tensile stress which a material is capable of developing. It is calculated from the maximum load carried during a tensile test and the original cross-sectional area of the specimen. The type of specimen to be used is prescribed in ISO 527 and 3268 (the latter deals exclusively with glass fibre composites and describes some special forms of test specimens). 

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