Vehicle Structure Reliability6.1.1 Basic Concepts(1) Reliabilitytheability of the item to remainfunctionalDefinition:the probabilitythat no operationalinterruptionswilloccurduring a statedtime intervalMission durationOperatingconditions行驶里程铁路条件气候条件行驶时间日历时间行驶速度Reguired function不发生安全性事件一一致命的能够正常行驶一一严重的不降低功能一一一般的不会引起维修一一轻微的
Operating conditions • 铁路条件 • 气候条件 • 行驶速度 Vehicle Structure Reliability 6.1.1 Basic Concepts (1) Reliability Definition： ◆the ability of the item to remain functional ◆the probability that no operational interruptions will occur during a stated time interval Mission duration • 行驶里程 • 行驶时间 • 日历时间 Required function 不发生安全性事件 —— 致命的 能够正常行驶 —— 严重的 不降低功能 —— 一般的 不会引起维修 —— 轻微的
Vehicle Structure Reliability6.1.1 Basic Concepts(1) ReliabilityR—R(t)Numerical statement:R(t) is the probability that no failure at item levelwilloccurintheinterval (O,t).R(0) = 1R(t)R(t) = P(T > t) = 「f(t)dtlim R(t) = 0t→01.00≤R(t)≤1R= R,R,R固有可靠度R,（lnherentReliability)使用可靠度Ru(Use Reliability)RR (Redundant Reliability)储存可靠度7
Vehicle Structure Reliability 6.1.1 Basic Concepts (1) Reliability Numerical statement： R(t) t 1.0 = = t R(t) P(T t) f(t)dt 0 ( ) 1 lim ( ) 0 (0) 1 = = → R t R t R t 7 R—R(t) R(t) is the probability that no failure at item level will occur in the interval (0, t). RI（Inherent Reliability） 固有可靠度 RU （Use Reliability） 使用可靠度 RR （Redundant Reliability） 储存可靠 度 R = RU RI RR
Vehicle Structure Reliability6.1.1 Basic Concepts(2) FailureMode: brittle rupture, creep, cracking, seizure, fatigue ...Cause:(1)intrinsicreason:weaknesses,wearout,(2) extrinsic reason: errors,misuse, mishandling during the designproduction,oruse.Effect: It can be different if considered on the item itself or at higherlevel.Ausualclassificationis non relevant,partial,complete,and criticalfailure.Sinceafailurecanalsocausefurtherfailures,distinctionbetweenprimaryandsecondaryfailureisimportant.Mechanism: Failure mechanism is the physical, chemical, or otherprocess resulting in a failure.8
Vehicle Structure Reliability 6.1.1 Basic Concepts (2) Failure ❖Mode: brittle rupture, creep, cracking, seizure, fatigue . ❖Cause: （1）intrinsic reason：weaknesses, wear out, （2）extrinsic reason：errors, misuse, mishandling during the design, production, or use. ❖Effect：It can be different if considered on the item itself or at higher level. A usual classification is non relevant, partial, complete, and critical failure. Since a failure can also cause further failures, distinction between primary and secondary failure is important. ❖Mechanism: Failure mechanism is the physical, chemical, or other process resulting in a failure. 8
Vehicle Structure Reliability6.1.1 Basic Concepts(3) Failure rate 入(t), MTTF, MTBF入(t) : 3 phases1(0)Early failures:BathtubCurveWearoutfailures:入(t) increases with time(t) decreasesrapidly with time;Failures with constant failure rate:入(t)isapproximatelyconstant9
λ(t) : 3 phases Vehicle Structure Reliability 6.1.1 Basic Concepts (3) Failure rate λ(t), MTTF, MTBF Wear out failures: λ(t) increases with time 9 Early failures: λ(t) decreases rapidly with time; Failures with constant failure rate: λ(t) is approximately constant Bathtub Curve
Vehicle Structure Reliability6.1.1 Basic Concepts(3) Failure rate, MTTF, MTBFNon-repairableMean time to failure (MTTF)> MTTFjsastatisticalvalueandismeant to bethemeanoveralongperiodoftimeandalargenumberof units.Meantimebetweenfailure (MTBF)Repairable&Non-repairable> MTBFisa reliabilityterm usedtoprovide the amountoffailurespermillionhoursforaproduct.10
Vehicle Structure Reliability 6.1.1 Basic Concepts (3) Failure rate, MTTF, MTBF Mean time to failure (MTTF) Mean time between failure (MTBF) 10 ➢ MTTF is a statistical value and is meant to be the mean over a long period of time and a large number of units. ➢ MTBF is a reliability term used to provide the amount of failures per million hours for a product. Non-repairable Repairable & Non-repairable