slide 1Chapter 1 – Design for lifetime performance and reliability2020

Questionnaires

Reliability Level 2:Read page 10, 11, 13…16 up to system reliabilityPrint this file (Reliability_Q2.pdf) and try to do the exercises on your own.All problems are linked to remote solutionsView them after your own attempt for solving.

σ σ σ± = +2 2x y x y

σ σ σ+ = =2 2ax b x xa a

σ σ σ σ µ σ µ= + +2 2 2 2 2 2x yxy x y y x

These expressions,for uncorrelated variables, are available in the exam,if applicable.

slide 2Chapter 1 – Design for lifetime performance and reliability2020

Problem R21An interference fit is realized with 20 H7/r6 hole/shaft tolerances. The tolerance fields are assumed to be normally distributed within a ±3σ interval.

a) Calculate the mean value μδ and the standard deviation σδ.

The torque T that can be transmitted is related by Tx=aδ where the a-value is a constant, δ is the diametrical interference and x is the probability of failure.

b) Calculate CV’=|T1-T50|/T50.

Variability Analysis of a Pressure Fit, two parameters

slide 3Chapter 1 – Design for lifetime performance and reliability2020

Problem R21 (6:27 min)(continued)

c) What could be an option for adapting the geometry of the components (shaft or hub), in order to obtain a more predictable torque that can be transmitted.

Variability Analysis of a Pressure Fit

Pressure Fit

slide 4Chapter 1 – Design for lifetime performance and reliability2020

Problem R22

The torque T that can be transmitted by a pressure fit is related by T=a∙μf∙δ where “a” is a constant, μf the coefficient of friction and δ the interference.

a) Derive the a-value (in N) from the calculated results presented in the next slide.

Variability Analysis of a Pressure Fit, two parameters

slide 5Chapter 1 – Design for lifetime performance and reliability2020

slide 6Chapter 1 – Design for lifetime performance and reliability2020

Problem R22 (8:58 min)(continued)

Torque T is expressed as z=a∙x∙y

Consider:CoF μx=0.2 and σx=0.02. Interference μy=30μm and σy=3μm.

b) Calculate μz and σz of the torque.

c) Calculate the CV’-value of the torque, assuming a 99.7% Confidence interval.

Variability Analysis of a Pressure Fit T=a∙μf∙δ

z=a∙x∙y

σz=σaxy

σz=aσxy

μz=a∙μx∙μy