For most materials v ≃ 0.3 for which G ≃ E/2.6. Modulus of Rigidity, G = E/2(1 + Poisson's ratio, v). 6.īut the material deteriorates rapidly in direct sunlight. Substantial creep occurs at much reduced stress levels, probably restricting applications to where the steady load is zero or very small, and the deflections are of short duration. Note, however, that protection from corrosion can often be given to materials which are poor in this respect by grease or surface treatments. Order of resistance on following scale: P-poor, M-moderate, G-good, E-excellent. Percentage of the conductivity of annealed high-purity copper at 20☌.
Fatigue strengths are reduced by poor surface finish and corrosion, and may continue to fall with increased cycles above 10 7. 2.įatigue strengths are typical for reversed bending of smooth finished specimens subjected to 10 7 cycles. Thinner strip and wire products can have higher yield strengths. Figures given are typical of fully heat treated and processed strip material of about 0.1 in thickness at room temperature. Very dependent on heat treatment and degree of working. High strength alloy steels: nickel maraging steel Elastic component has to operate in a potentially corrosive environment (includes ‘normal’ atmospheres)Īppropriate, good, corrosion resistance, especially if requirements 8 or 10 have to be metĪpproximate maximum continuous operating temperature in airĬarbon chromium stainless steel (BS 420 S45) Elastic component has to operate at high or low temperatureĪs for 1–10 above, but properties, for example strength, must be those at the operating temperatureġ2. against copper (or other circuit conductor) and low temperature coefficient of electrical conductivityġ1. As 6 but current has to be measured accurately by system of which elastic component is a part Low temperature coefficient of thermal expansion and elastic modulus (E or G)ġ0. As 8 and may be subject to temperature fluctuations Negligible hysteresis and elastic after-effect non magneticĩ. Elastic component has to provide the main reactive force in a sensitive measurement or control system Elastic component has to provide a heat pathĨ. Elastic component has to carry an electric currentħ. U is not a material property but emphasises the value of being able to manufacture the suspension material as thin flat stripĦ. High f 2 max × U/G: G = shear modulus, U = aspect ratio (width/thickness) of suspension cross-section. Torsion suspension with minimum stiffness for a given suspended load High 1/E: note that stiffness can be made zero or negative by suitable pivot geometry designĥ. Flexure hinge with minimum stiffness (for a given pivot geometry) Flexure hinge with the maximum load capacity for a given size and movementĤ. Flexure hinge with maximum movement for a given sizeģ. Unless the application involves a sufficiently large number of stress cycles for fatigue to be the critical condition, in which case:Ģ.
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