Uniaxial fatigue test

Figure 7.9 Uniaxial fatigue test of SABIC Innovative Plastics Ultem polyetherimide compounds with different glass fiber content [1 ]. 

A series of uniaxial fatigue tests on unnotched plastic sheets show that the fatigue limit for the material is 10 MN/m. If a pressure vessel with a diameter of 120 mm and a wall thickness of 4 mm is to be made from this material, estimate the maximum value of fluctuating internal pressure which would be recommended. The stress intensity factor for the pressure vessel is given by F = 2tjg(2a) where ae is the hoop stress and a is the half length of an internal defect. 

All of the uniaxial fatigue data reported to date have been generated using a fatigue testing machine built by MRC that is based on the principal of a wobble plate. The machine has positions for 30 specimens and is capable of operation at controlled... 

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. 

Fig. 4.66 Loading states of the continuous oscillation test for uniaxial fatigue loading.

It should be noted that there are subtle differences when comparing data generated in uniaxial tension and flexural fatigue tests. A imiaxially applied load nominally imposes a uniform normal stress throughout the cross section of the specimen, with a plane strain condition occurring at the specimen s center. In contrast, the normal stresses in a flexure test are linearly distributed across the specimen, with the maximum occurring at the outer surfaces of the specimen, and... 

Sequenced tests. This test is quite similar to a fatigue test. The elastomer sheet or film were cut into rectangular strips of width 15mm, and tested in uniaxial tension with 30 mm between the grips. Extension was measured by the clamp displacements. The test consisted of eight load-unload cycles... 

Furthermore, anticipated in-service conditions may call for conducting simulated laboratory fatigue tests that use either uniaxial tension-compression or torsional stress cycling instead of rotating-bending. 

The plastic strain energy density can be physically interpreted as the energy of distortion associated with the change in shape of a volume elanent and is related to failure, particularly under conditions of ductile behavior, as it often occurs in many of the polymeric materials submitted to cyclic mechanical solicitation (Kanchanomai and Mutoh, 2004). According to the mathematical model proposed by Morrow (American Society for Testing and Materials, 1965), the strain energy density can be evaluated numerically as the inner area of the saturated hysteresis loop for the uniaxial fatigue experiments (Fig. 7.6), and is expressed mathematically as ... 

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. 

While lab tests often employ simple uniaxial loads, rubber components in service commonly experience states that combine loads from multiple directions. Such loads are said to be multiaxial. Fracture and fatigue processes occurring under such loads are governed by the same general principles as for uniaxial loads, but additional consideration must be made to account for the way in which local effects on crack precursors depend on orientation. 

Wang SS, Chim ES-M, Socie DF. Stiffness degradation of fiber-reinforced composites under uniaxial tensile, pure torsional, and biaxial fatigue at cryogenic temperature. In Composite materials testing and design. ASTM STP 787 EB 1982. pp. 287-301. 

Conventional tests such as the well-known Wohler test to analyse the fatigue resistance of polymers are based on oscillating, mostly sinusoidal loading of a specimen at uniaxial tensile (or compression) or... 

Fig. 4.67 Test equipment for uniaxial tension/compression fatigue loading.

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. 

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