Uniaxial test

Determination of the fourth-rank tensor term F. 2 remains. Basically, F.,2 cannot be found from any uniaxial test in the principal material directions. Instead, a biaxial test must be used. This fact should not be surprising because F-,2 is the coefficient of the product of a. and 02 in the failure criterion. Equation (2.140). Thus, for example, we can impose a state of biaxial tension described by a, = C2 = c and all other stresses are zero. Accordingly, from Equation (2.140),... 

The value of F,2 then depends on the various engineering strengths plus the biaxial tensile failure stress, a. Tsai and Wu also discuss the use of off-axis uniaxial tests to determine the interaction strengths such as F.,2 [2-26]. 

For a lower bound on the apparent Young s modulus, E, load the basic uniaxial test specimen with normal stress on the ends. The internal stress field that satisfies this loading and the stress equations of equilibrium is... 

Even plastics with fairly linear stress-strain curves to failure, for example short-fiber reinforced TSs (RPs), usually display moduli of rupture values that are higher than the tensile strength obtained in uniaxial tests wood behaves much the same. Qualitatively, this can be explained from statistically considering flaws and fractures and the fracture energy available in flexural samples under a constant rate of deflection as compared to tensile samples under the same load conditions. These differences become less as the... 

Although nearly all creep and stress-relaxation tests are made in uniaxial tension, it is possible to make biaxial tests in which two stresses are applied at 90° to one another, as discussed in Section VI. In a uniaxial test there is a contraction in the transverse direction, but in a biaxial test the transverse contraction is reduced or even prevented. As a result, biaxial creep is less than uniaxial creep--in cquihiaxial loading it is roughly hall as much for equivalent loading conditions. In the linear region the biaxial strain 2 in each direction is (255.256)... 

The uniaxial test is widely used for quality control and formulation testing for obvious reasons. The JANAF configuration is not likely to be replaced for these purposes, especially since the backlog of information relative to the formulation art is composed primarily of data from this specimen. Grain structural analysts require more precise information, however, and when uniaxial data are obtained for their purposes, more elaborate and time-consuming tests may be conducted. 

Although the uniaxial test has traditionally received the most attention, such tests alone may be insufficient to characterize adequately the mechanical capability of solid propellants. This is especially true for ultimate property determinations where a change in load application from one axis to several at once may strongly affect the relative ranking of propellants according to their breaking strains. Since the conditions usually encountered in solid rocket motors lead to the development of multiaxial stress fields, tests which attempt to simulate these stress fields may be expected to represent more closely the true capability of the material. 

Fatigue data of corrosion resistant steels and other relevant high strength materials are easy available for non-corrosive ambiance (air, oil). For the large variety of liquids applied in production processes the data have to be evaluated from special fatigue tests with corrosion cells. This paper answers the question if such uniaxial test results can be applied for the real component design in order to meet three-axial corrosion fatigue reality well. 

The corrosion fatigue data from uniaxial tests can be transmitted to the notched pulsating pressure loaded components quantitatively or with additional safety. The uniaxial pulsating stress yields to be the stricter criterion. 

A constant tensile-stress method is outlined in ISO 6252, in which a test specimen is exposed to a constant tensile force while immersed in a stress cracking agent so as to determine the time to rupture under a specified stress. This uniaxial test leads to the determination of the lifetime of the specimen with accuracy, but it is time consuming and requires complex equipment. Variations of this test include a tensile creep test that monitors the strain and a monotonic creep test that uses a constant stress rate instead of a fixed stress [1]. 

There has been a report from Japan recently31, of a large-scale version of the uniaxial test, applicable to coarse granular materials like coal and limestone containing particles up to 50 mm in size. Although such coarse materials are outside the scope of this report, the test still deserves a mention here because it is a logical extension of the tests reported in the two previous sections. 

After making the calculations, results must be analyzed. For fiber RP parts, special failure hypotheses have been developed, distinguished by type of load (static or dynamic), evaluation of failure type (failure of fiber, matrix, or interface) and preference given to either high strength or maximum strain. As with failure hypotheses for conventional materials, it should be possible to make a comparison between multi axial loading conditions and reference values obtained from uniaxial tests. 

For linear elastic materials, Hooke s Law is a constitutive relationship between stress and strain. There have been substantial efforts in identifying similar relationships for plastic solids. In uniaxial tests, the portion of the true stress-true strain curve beyond yielding is often described by... 

The latter are mainly based on the calculation of Dressing the internal energy absorbed by the material as compared to the maximum energy allowable in uniaxial tests. 

Seam strengths in uniaxial tests parallel to the threads... 

Proposal for a uniaxial test to estimate shear stiffness. 

Uniaxial stress-strain curve of ETFE-foils (uniaxial test, qualitative diagram). 

Where a condition of combined fatigue stresses exists the application of uniaxial test data may not be directly relevant. Therefore, a rigorous design assessment will require a suitable test programme. However, as a conservative approach the damage indicator method given in the EUROCOMP Design Code will yield a safe result. 

In many film applications the product is subjected to puncture or impact loads. These types of loads are applied perpendicular to the plane of the film. Therefore, the stresses act biaxially (in both the machine and transverse directions simultaneously) and are not represented well by a uniaxial test. Impact resistance tests are designed to biaxially load the film to measure its energy absorbing capability. 

The strain values observed at the maximum load point during a biaxial test are lower than in the case of the uniaxial test performed with same dimension samples and this for the two directions. As a consequence, the strains at which the load is maximum are lower than 4.5% in the weft direction during the uniaxial test. These strain values represent the limit from which a loss of fiber density takes place in the tows and this phenomenon should probably be avoided by keeping the tensile strain in the tetrahedron preform lower than these values. 

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