Đang chuẩn bị liên kết để tải về tài liệu:
Designing Capable and Reliable Products Episode 2 Part 2

Tham khảo tài liệu 'designing capable and reliable products episode 2 part 2', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Case studies 205 Figure 4.41 SSI models for the solenoid assembly failure modes where A cross-sectional area J polar second moment of area. An approximate relationship is commonly used to determine the torque for assembly M for a given pre-load F Shigley and Mischke 1996 . It is a standard formulation for bolts and fasteners determined from experiment and is related to the friction found in the contacting surfaces of the parts on assembly. M KFD 4.72 where K torque coefficient or nut factor . Therefore combining the above equations in terms of the shear stress gives T FLKFDr r - d4 4.73 206 Designing reliable products The principal stresses at the relief section 5 and 52 are found from 5j j2 0.55 Vo.25 4.74 Using von Mises Theory from equalion 4.58 the probabilistic requirement p to avoid yield in a ductile material but under a biaxial stress system is used to determine the reliability R as R p sy ỵ sị sị-SỵS 4.75 Stress in service The shear stress T due to the assembly torque diminishes to zero with time the preload F remaining constant and so the stress on the solenoid section is only the direct stress s as given in equation 4.75 see Figure 4.41 b Edwards and McKee 1991 . A second reliability can then be determined by considering the requirement that the pre-load stress remains above a minimum level to avoid loosening in service 0.5Spmin from experiment Marbacher 1999 . The reliability R can then be determined from the probabilistic requirement p to avoid loosening R P L PSSp 4.76 Determining the design variables Before a probabilistic model can be developed the variables involved must be determined. It is assumed that the variables all follow the Normal distribution and that they are statistically independent i.e. not correlated in anyway. The scatter of the pre-load F using an air tool with a clutch is approximately 30 of the mean which gives the coefficient of variation cv 0.1 assuming ĩơ covers this range therefore ơp 0.1 4.77 For the torque coefficient K .