Shaft Yield stress

This stress is only a quarter of the yield stress of a typical structural steel, and the shaft therefore has an ample factor of safety against failure by plastic overload. 

The vane viscometer is yet another form of the concentric cylinder instrument, in which the bob is replaced by a rotor with four blades or vanes each attached by one edge to a vertical shaft, at 90° intervals around the shaft (Figure 22.7). This geometry, which can be used either with a cup or in the infinite sample mode, is particularly useful for measuring yield stress, and can also be used to measure the rheological properties of non-Newtonian liquids. Its advantages are described by Gunasekaran and Ak (2002). 

The maximum shear stress criterion, also called Tresca s criterion, would predict failure when the shear stress in the shaft equals the shear yield stress (determined by a tensile test). By stress resolution, the shear stress in a tensile test is equal to the normal stress divided by two. Hence the shear stress to produce yield for the material of interest here would be Oq/2, so that failure of the shaft is predicted when... 

The allowable yield stress Ty of the shaft material under pure tensional loading is obtained from the yield stress in simple tension a-y since from the shear strain energy theory of failure ... 

Table 13.1 Typical yield stresses for shaft material...

It is required to find the torque without slippage that can be transmitted by a hub that is assembled by an interference fit to a powered shaft. The hub outside diameter D = 070 mm, and the shaft diameter d = 050 mm, as shown in Figure 4.55. The length of the hub is 100 mm. Both hub and shaft are machined from hot rolled steel SAE 1035 with a yield strength Sy A(342,26) MPa (see Table 4.6). Given that the hub is stopped suddenly in service due to a malfunction, and considering only the torsional stresses, what is the probability that the shaft will yield ... 

Chemical and processing towers, condensers. Furnace parts such as retorts and low stressed parts subject to temperatures up to 800 "C. Type 430 nitric-acid storage tanks, furnace parts, fan scrolls. Type 430F-pump shafts, instrument parts, valve parts Products requiring high yield point and resistance to shock... 

The octahedral shear stress criterion, also called the maximum energy of distortion criterion or the Von Mises theory, would predict the following torque at yield. For the shaft the octahedral shear stress would be (from Equation 3)... 

Combined stress is greater than the material yield strength. Shaft is too small try sh = 0.114 m (4 inch)... 

If the available materials to construct the shaft are a ceramic with i2m = 400 MPa or the aluminium alloy AlSilMgMn with Rpo.2 = 202 MPa and Rm = 237 MPa, we can expect the ceramic to fail because the stress at the notch root is much larger than the tensile strength. For the aluminium alloy, the tensile strength is also exceeded, and we thus might expect its failure as well. However, the calculation is not valid in the case of a ductile material, for equation (4.1) is valid only for a linear-elastic material, whereas the alloy AlSi 1 MgMn yields at Rpo.2 = 202 MPa. This increases the strain at the notch root and reduces the stress concentration. The actual stress at the notch root cannot be calculated with the tools introduced so far. In the next section, we will discuss Neuber s rule that allows to estimate the stresses. 

On this basis, the shaft of the pump is designed. Due to fatigue considerations, the maximum stress should be smaller than the lesser of 18% yield, or 30% ultimate tensile strength. 

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