PSI - Issue 46

Seong-woo Woo et al. / Procedia Structural Integrity 46 (2023) 169–174 Seong-woo Woo et al. / Structural Integrity Procedia 00 (2021) 000–000

171

3

2. Parametric ALT for Mechanical System 2.1. Introduction

In a mechanical product, movements of power for acquiring mechanical advantages are utilized in functions that require forces and movement by accommodating certain system mechanisms. It will be subjected to repeated stress due to loads. If there is a void (design flaw) in the structure where the loads are implemented, the mechanical product will be unexpectedly unsuccessful in its lifetime. After discovering the product failure by investigation like parametric ALT, engineer will optimally design the product shape and material type to overcome its own loads. Stress is a material quantity that specifies the inner forces which adjoining particles of a continuum material exert on each other. For a mechanical system, because stress originates from effort such as force, it might be stated as (1)

kT E a

kT E a

  

  

  

  

 

 

n







exp

exp

 TF AS

Be

where A and B are constants. Design flaws in products can be established by exerting larger effort under the elevated circumstances. That is, accelerated factor (AF) may be restated to integrate the effort ideas:

   n



  

   

  

     

  

   k T T E a  0 1 1 1

  

  

  

   k T T E a  0 1 1 1

S S

e

AF



0 1

0 1

e

(2) Based on the lifetime target of the test plan, to attain the mission cycle in a parametric ALT, the sample size equation with the AF may be stated as [1]:



  

   

AF h L BX  *

x 1

      1

n r

r

a

(3) 2.2. Case Study - Reliability Design of a Problematic Cooling Enclosure System in a Refrigerator returned from the Field

Fig. 2. A damaged evaporator tube in a cooling enclosure after usage.