BPT2423 STATISTICAL PROCESS CONTROL CHAPTER OUTLINE Fundamental Aspects Product Life Cycle Curve Measures of Reliability Failure Rate Mean Life and Availability Calculating System Reliability ID: 385679
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Slide1
RELIABILITY
BPT2423 – STATISTICAL PROCESS CONTROLSlide2
CHAPTER OUTLINE
Fundamental Aspects
Product Life Cycle Curve
Measures of Reliability
Failure Rate, Mean Life and Availability
Calculating System Reliability
Reliability EngineersSlide3
LESSON OUTCOMES
Known
the importance of system reliability
Identify on how performance during the life of a product, process or system is affected by its design and configuration
Able to compute the reliability of systems including systems in series, parallel and hybrid combinationsSlide4
FUNDAMENTAL ASPECTS
Reliability (quality over the long term) is the
ability of a product to perform its intended function over a period of time and under prescribed environmental conditions
Reliability of component dependent on many factors:
quality of research performed at its conception
the original design and any subsequent design changes
the complexity of the design
the manufacturing processes
the handling received during shipping
the environment surrounding its use
the end users and etc. Slide5
FUNDAMENTAL ASPECTS
Reliability testing
enables a company to better comprehend how their products will perform under normal usage as well as extreme or unexpected situations
Reliability programs
provide information about product performance by systematically studying the product
Four factors associated with reliability:
Numerical value
Intended function
Life
Environmental conditionsSlide6
LIFE-HISTORY CURVESlide7
Life cycle of a product is commonly broken down into 3 phases:Early failure (infant mortality)phase is characterized by failures occurring very quickly after the product has been produced or put into use by the consumer the curve during this phase is exponential with the number of failures decreasing the longer the product is in use
some early failures are due to inappropriate or inadequate materials, marginal components, incorrect installation or poor manufacturing techniques
LIFE-HISTORY CURVESlide8
Chance failureDuring the failure, portion of a product’s useful life, failures occur randomlyMay be due to inadequate or insufficient design marginsMisapplication or misuse of the product by the consumer can lead to product failure – eg.: overstressing
Wear-out
Failures increase in number until few, if any of the product are left
Due to a variety of causes such as related to actual product function or cosmetic (scratched, dented, discolorations, misalignments and interference between components)
LIFE-HISTORY CURVESlide9
MEASURES OF RELIABILITY
Overall system reliability
depends on the individual reliabilities
associated with the parts, components and subassemblies
Reliability values
are sought to determine the performance of a product, reveal any recurring patterns of failure and the underlying causes of those failures
Reliability test
determine what failed, how it failed and the number of hours, cycles, actuations or stresses it was able to bear before failure
If result known, decisions can be made concerning product reliability expectations, corrective action steps, maintenance procedures and cost of
repair/replacementSlide10
MEASURES OF RELIABILITY
Several different types of test exist to judge the reliability of a product :
Failure-terminated test
Ended when a predetermined number of failures occur within the sample being tested
Decision concerning whether or not the product is acceptable is based on the number of products that have failed during the test
Time-terminated test
Concluded when an established number of hours is reached
Product is accepted on the basis of how many products failed before reaching the time limit
Sequential Test
- r
elies on the accumulated results of the testsSlide11
MEASURES OF RELIABILITY
Determine Failure Rate,
λ
Determine Average Life,
θ
or
Determine AvailabilitySlide12
MEASURES OF RELIABILITY
Example :Determine the failure rate for a 90-hour test of 12 items where 2 items fail at 45 and 72 hours, respectively. What is the mean life of the product?
λ
=
2
45 + 72 + (10) 90
= 2 / 1017
= 0.00197
θ
= 1 /
λ
= 1 / 0.00197
= 507.6 hoursSlide13
SYSTEM RELIABILITY
Reliability is the probability that a product will not fail during a particular time period.
where :
s – those units performing satisfactorily
n – total number of units being tested
Reliability in SeriesSlide14
SYSTEM RELIABILITY
Reliability in Parallel
Reliability in Redundant Systems and Backup Components
r
1
r
bSlide15
SYSTEM RELIABILITY
Calculation :
Example:Slide16
A paranoid citizen has installed the home alert system shown below. What is the overall system reliability?
SYSTEM RELIABILITY
Exercise
: