Question

The question is to estimate the maximum value of F that would not cause eventual fatigue failure of the bolts. Given that SAE CLASS= 8.8 , D= 24 mm, SF=2

Two bolts with rolled threads (see table 10.6 of the textbook), are used to attach a pillow block, as shown in the figure below. Please select the grade (SAE Class) and the size of the bolts (nominal diameter) from the table (see next page) and refer to the tables 10.5 and 10.2 of the textbook, respectively. The bolts are initially tightened In accordance with the equation F1 = 0.9. A. Sp. Joint stiffness is estimated to be three times bolt stiffness. Bolt bending may be assumed negligible. During operation, the external load tending to separate the pillow block from its support varies rapidly between 0 and F. Estimate the maximum value of F that would not cause eventual fatigue failure of the bolts (assume an idealised stress-strain curve based on Sy). Please consider a safety factor SF of 2. (15 marks) AF Rotating shaft Pillow block Metric (ISO) screw

Answer 1

0 Ansi Grun that det us Consider that, bolt SAE class=8.8. d=29mm for diameter d -24mm. Tensile stress alea (U) - 353 mnt (from table s-D fá SAE class 8.8, Rusof storength ($p6001120. [from tabte 8-10). Proload fi=019 (A)(Sp) fe - 0.9(353)C600) fi 190620N. Load Varies o tof, from per Lood bolt FN N=no. boet g 1-2 load per bolt = f/2. 80 Pmax = F/2. § pmin=0 Belt will experience fleectuating forces Buch as formin = Omin+f; foman c Pmaxt fi where, C = Joint Constant, C- Kb Kytkm bolt joint stiffnes. km a member stiyness. g

w and (km = 316] Gireen, ko Kg +316 Mb G46 , 0.25 Po, from @ 40 fomin (0.25%0)+190620.- 1906200 foman = 60.25)(42)+190620. = 0,1256 +190620N. The Alternating Bless experienced by (fomax - Fomin)/2 a belt is, a At CO1267 +190820-190020112 353 ba 011256 353X2 ба 0.125F 706 a bolt is, The miar sbreas midrange experienced by (flomax & Fomin)/2 m At 60.125€ +190620 +190620)/2 353 0.125F +381240 706 The fatigue factor of safety is gireen by,

bo ng Se (Sut - 6;) Sutfat Selam-6) where, 6; At 190620 353 SCOMPa. and sut 830MPa. (from läble 8-117 Se - 129 MPa (from table 8-11]. 6 = 2Cgiven). So, Noco, South 2 = 1296830-540) 830 (0:125F 10.125F +381290 +129 706 706 -540 0.2939094 +0104568F+39320-139320=1296290) 0.339589 F = 37140 ft 37140/0.339589 F110162N f110.1626 Maxinurn value gt that would not cause eventual the bolts. gth fatigue