91430 SPS cover edited - Electronic Fasteners Inc

electronicfasteners.com

91430 SPS cover edited - Electronic Fasteners Inc

mine the clamping stress at assembly conditions, theelongation should be multiplied by the modulus ofelasticity at room temperature..0033 30.6 10 6 = 101,145 psiThe assembly conditions will be affected by thedifference between th ideal and actual coefficients ofexpansion of the joint. The ideal coeffienct for the fastenermaterial was calculated to be 7.05 but the closestmaterial – H-11 – has a coefficient of 7.1. Since thismaterial has a greater expansion than calculated, therewill be a reduction in clamping force resulting from theincrease in temperature. This amount equals the differencebetween the ideal and the actual coefficientsmultiplied by the change in temperature, the length ofthe fastener, and the modulus of elasticity at 70°F.[(7.1 – 7.05) 10 –6 ][800 – 70][1.333] [30.6 10 6 ] = 1,490 psiThe result must be added to the initial calculatedstresses to establish the minimum required clampingstress needed for assembling the joint at roomtemperature.101,145 + 1,490 = 102,635 psiFinally, the method of determining the clampingforce or preload will affect the final stress in the joint atoperating conditions. For example, if a torque wrench isused to apply preload (the most common and simplestmethod available), a plus or minus 25 per cent variationin induced load can result. Therefore, the maximum loadwhich could be expected in this case would be 1.5 timesthe minimum, or:(1.5)(102,635) = 153,950 psiThis value does not exceed the room-temperatureyield strength for H-11 given in Table 19.Since there is a decrease in the clamping force withan increase in temperature and since the stress at operatingtemperature can be higher than originally calculatedbecause of variations in induced load, it is necessary toascertain if yield strength at 800°F will be exceeded(max stress at 70°F + change in stress) E at 800°FE at 70°F[153,950 + (–1490)] 24.6 10 6 = 122,56530.6 10 6This value is less than the yield strength for H-11 at800°F, Table 19. Therefore, a 1/4-28 H-11 bolt stressedbetween 102,635 psi and 153,950 psi at room temperaturewill maintain a clamping load 1500 lb at 800°F after1000 hr of operation. A cyclic loading of 100 lb, whichresults in a bolt loading between 1500 and 1600 lb willnot cause fatigue failure at the operating conditions.Table 16PHYSICAL PROPERTIES OF MATERIALS USED TO MANUFACTURE ALLOY STEEL SHCS’SCoefficient of Thermal Expansion, µm/m/°K 120°C to 100 200 300 400 500 60068°F to 212 392 572 752 932 1112Material5137M,51B37M 2 – 12.6 13.4 13.9 14.3 14.64137 3 11.2 11.8 12.4 13.0 13.6 –4140 3 12.3 12.7 – 13.7 – 14.54340 3 – 12.4 – 13.6 – 14.58735 3 11.7 12.2 12.8 13.5 – 14.18740 3 11.6 12.2 12.8 13.5 – 14.1Modulus of Elongation (Young’s Modulus)E = 30,000,000 PSI/in/inTable 19 - Yield Strength at Various TemperaturesAlloy–––––––– Temperature (F) ––––––––70 800 1000 1200Stainless SteelsType 302 35,000 35,000 34,000 30,000Type 403 145,000 110,000 95,000 38,000PH 15-7 Mo 220,000 149,000 101,000 –High Strength Iron-Base Stainless AlloysA 286 95,000 95,000 90,000 85,000AMS 5616 113,000 80,000 60,000 40,000Unitemp 212 150,000 140,000 135,000 130,000High Strength Iron-Base AlloysAISI 4340 200,000 130,000 75,000 –H-11 (AMS 6485) 215,000 175,000 155,000 –AMS 6340 160,000 100,000 75,000 –Nickel-Base AlloysIconel X 115,000 - - 98,000Waspaloy 115,000 - 106,000 100,000NOTES:1. Developed from ASM, Metals HDBK, 9th Edition, Vol. 1 (°C = °K for values listed)2. ASME SA5743. AISI4. Multiply values in table by .556 for µin/in/°F.70

More magazines by this user
Similar magazines