《纺织复合材料》课程参考文献（Composite Materials Handbook，Volume 3）Chapter 7 - Damage Resistance, Durability, and Damage Tolerance

MIL-HDBK-17-3F Volume 3,Chapter 7-Damage Resistance,Durability,and Damage Tolerance Selected BVID Establishes DUL Capability (Design Value)For FAR 25.305 Analysis 6uans .MS=0.0 at DUL Selected MDD Establishes DLL Capability (Design Value) For FAR 25.571(b)Analysis Selected Max DSD lenp! MS =0.0 at DLLEstablishes Capability for FAR 25.571(e)Analysis !seH Detectable Readily Immediately Detectable Obvious 1e ADL CDT Damage Size BVID:Barely visible impact damage DLL:Design limit load DUL:Design ulimate load DSD:Discrete source damage MDD:Maximum design damage RDD:Readily detectable damage ADL:Allowable damage limit MS:Margin of safety CDT:Critical damage thershold FIGURE 7.2.2.3(a)Residual strength requirements versus damage size. 1.Barely visible impact damage(BVID)establishes the strength design values to be used in analy- ses demonstrating compliance with the regulatory Ultimate Load requirements of FAR 25.305. For small aircraft and different classes of rotorcraft the corresponding requirements are 23.305. 27.305 and 29.305.In the case of small aircraft,the BVID static strength requirement has been added to the regulation for composite damage tolerance,FAR 23.573.The extent of such dam- age needs to be established as part of criteria defined prior to the design phase.The term visible is used since the primary inspection method in current use involves visual observation.An upper limit of 100 ft-Ib(140 Joules)on the BVID impact energy level is applied based on this value be- ing at the upper limit of what could be realistically expected. 2.Allowable damage limits(ADL),defined as damage that reduces the residual strength to the regu- latory Ultimate Load requirements of FAR 25.305,are determined to support maintenance docu- ments.Given that the structure's strength with BVID damage will result in positive margins at design Ultimate Load(DUL),the corresponding ADL will generally be larger than the BVID(see Figure 7.2.2.3(a)).Characteristics describing the detectability of the ADL as well as the type and extent of the damage are documented to support maintenance programs. 3.Maximum design damage(MDD)establishes the strength design values to be used in analyses demonstrating compliance with the regulatory damage tolerance requirements of FAR 25.571(b). In the case of small aircraft,the regulation for composite damage tolerance,FAR 23.573,while analogous rotorcraft rules can be found in 27.571 and 29.571.Current efforts are underway to develop a unique composite damage tolerance rule for rotorcraft,which will be given the numbers 27.573 and 29.573,depending on the class of rotorcraft.The extent of such damage needs to be established as part of criteria defined prior to the design phase. 4.Critical damage thresholds(CDT)are defined as damages that reduce the residual strength to the regulatory requirements of FAR 25.571(b)(or the equivalent for other types of aircraft).Given that the structure's strength with MDD-sized damage will result in positive margins at design Limit Load(DLL),the corresponding CDT will be larger than the MDD.Characteristics describing the detectability of the CDT as well as the type and extent of the damage are documented to support the establishment of required inspection methods and intervals.Using the selected inspection 7-16

MIL-HDBK-17-3F Volume 3, Chapter 7 - Damage Resistance, Durability, and Damage Tolerance 7-16 FIGURE 7.2.2.3(a) Residual strength requirements versus damage size. 1. Barely visible impact damage (BVID) establishes the strength design values to be used in analy￾ses demonstrating compliance with the regulatory Ultimate Load requirements of FAR 25.305. For small aircraft and different classes of rotorcraft the corresponding requirements are 23.305, 27.305 and 29.305. In the case of small aircraft, the BVID static strength requirement has been added to the regulation for composite damage tolerance, FAR 23.573. The extent of such dam￾age needs to be established as part of criteria defined prior to the design phase. The term visible is used since the primary inspection method in current use involves visual observation. An upper limit of 100 ft-lb (140 Joules) on the BVID impact energy level is applied based on this value be￾ing at the upper limit of what could be realistically expected. 2. Allowable damage limits (ADL), defined as damage that reduces the residual strength to the regu￾latory Ultimate Load requirements of FAR 25.305, are determined to support maintenance docu￾ments. Given that the structure’s strength with BVID damage will result in positive margins at design Ultimate Load (DUL), the corresponding ADL will generally be larger than the BVID (see Figure 7.2.2.3(a)). Characteristics describing the detectability of the ADL as well as the type and extent of the damage are documented to support maintenance programs. 3. Maximum design damage (MDD) establishes the strength design values to be used in analyses demonstrating compliance with the regulatory damage tolerance requirements of FAR 25.571(b). In the case of small aircraft, the regulation for composite damage tolerance, FAR 23.573, while analogous rotorcraft rules can be found in 27.571 and 29.571. Current efforts are underway to develop a unique composite damage tolerance rule for rotorcraft, which will be given the numbers 27.573 and 29.573, depending on the class of rotorcraft. The extent of such damage needs to be established as part of criteria defined prior to the design phase. 4. Critical damage thresholds (CDT) are defined as damages that reduce the residual strength to the regulatory requirements of FAR 25.571(b) (or the equivalent for other types of aircraft). Given that the structure’s strength with MDD-sized damage will result in positive margins at design Limit Load (DLL), the corresponding CDT will be larger than the MDD. Characteristics describing the detectability of the CDT as well as the type and extent of the damage are documented to support the establishment of required inspection methods and intervals. Using the selected inspection

MIL-HDBK-17-3F Volume 3,Chapter 7-Damage Resistance,Durability,and Damage Tolerance technique,realistic damages smaller than the corresponding CDT are shown to be detectable with high probability before any growth causes it to exceed the CDT. 5.Readily detectable damage(RDD)can be detected within a small number of flights during routine aircraft servicing.For damage that is not readily detectable,the structure should be evaluated for all possible damage growth mechanisms.The maximum extent of damage that is considered readily detectable,but which is not immediately obvious,should be established.The advisory cir- cular for damage tolerance,ACJ 25.571(a),allows the residual strength of RDD to be confirmed at load levels less than the regulatory loads specified in FAR/JAR 25.571(b)(Reference 7.2.2.3(0). 6.Damages larger than the maximum RDD are considered to be immediately obvious.Except for damage resulting from in-flight discrete sources(rotor burst,bird strike,etc.),no residual strength analysis is required for obvious damage. The residual strength curve shown in Figure 7.2.2.3(a)starts near ultimate strength and spans the range to discrete source damage sizes.This range encompasses damage conditions critical to meeting all requirements such as: 1.Damage sizes and states which support the ADL(Ultimate Load levels)and repairable damage sizes to be placed into the Structural Repair Manual; 2.CDT damages for Limit Load design values; 3.RDD for less than Limit Load but greater than continued safe flight load design values;and 4."Discrete source"damage for continued safe flight load design values. Test data and analysis methods developed by the Boeing-NASA/ACT program(References 7.2.2.3(j) through 7.2.2.3(1))show that the inspection methodologies and damage growth mechanisms should be established to ensure accidental damage occurring in service can be found and repaired before compro- mising limit strength capabilities.Visual inspection is the preferred damage detection method,and the no-growth approach for damages less than Limit Load size has been the basis for certification.For new composite primary structure application,these approaches will require revalidation. Figures 7.2.2.3(b)and 7.2.2.3(c)identify the inspection decision points,requirements,development tasks,analyses and actions required to meet the damage tolerance requirements of a principal structural element(PSE).Figure 7.2.2.3(b)outlines the levels of damage tolerance requirements and can be used for test,analysis and maintenance planning.Figure 7.2.2.3(c)defines the flow of events and actions to be used to develop the data required for damage tolerance certification. The deterministic compliance method is based on a minimum of two sets of testing and analysis.The first set is designed to show positive margins of safety at design Ultimate Load with BVID size damages. This testing includes mostly coupons and subcomponents containing BVID.The second set of testing is designed to show positive margins of safety with large damage at design Limit Load.This testing in- cludes subcomponent (e.g.,five-stringer panels)and component structures with through the thickness damage,skin-stiffener debonds,large impact damages,etc.These types of damage are considered to be maximum design damage(MDD).Tests are used to show MDD-sized damage is easily detectable. Tests are also used to show MDD-sized damage and smaller will not grow under operational loads Although this method meets FAA requirements for damage tolerance,it may not provide enough data to support the definition of accurate ADLs in structural repair manuals.Consequently,allowable damage sizes are conservatively set to smaller values.This has had the effect of increasing in-service repair costs of thin composite honeycomb sandwich panels in commercial aircraft. 7-17

MIL-HDBK-17-3F Volume 3, Chapter 7 - Damage Resistance, Durability, and Damage Tolerance 7-17 technique, realistic damages smaller than the corresponding CDT are shown to be detectable with high probability before any growth causes it to exceed the CDT. 5. Readily detectable damage (RDD) can be detected within a small number of flights during routine aircraft servicing. For damage that is not readily detectable, the structure should be evaluated for all possible damage growth mechanisms. The maximum extent of damage that is considered readily detectable, but which is not immediately obvious, should be established. The advisory cir￾cular for damage tolerance, ACJ 25.571(a), allows the residual strength of RDD to be confirmed at load levels less than the regulatory loads specified in FAR/JAR 25.571(b) (Reference 7.2.2.3(i)). 6. Damages larger than the maximum RDD are considered to be immediately obvious. Except for damage resulting from in-flight discrete sources (rotor burst, bird strike, etc.), no residual strength analysis is required for obvious damage. The residual strength curve shown in Figure 7.2.2.3(a) starts near ultimate strength and spans the range to discrete source damage sizes. This range encompasses damage conditions critical to meeting all requirements such as: 1. Damage sizes and states which support the ADL (Ultimate Load levels) and repairable damage sizes to be placed into the Structural Repair Manual; 2. CDT damages for Limit Load design values; 3. RDD for less than Limit Load but greater than continued safe flight load design values; and 4. “Discrete source” damage for continued safe flight load design values. Test data and analysis methods developed by the Boeing-NASA/ACT program (References 7.2.2.3(j) through 7.2.2.3(l)) show that the inspection methodologies and damage growth mechanisms should be established to ensure accidental damage occurring in service can be found and repaired before compro￾mising limit strength capabilities. Visual inspection is the preferred damage detection method, and the no-growth approach for damages less than Limit Load size has been the basis for certification. For new composite primary structure application, these approaches will require revalidation. Figures 7.2.2.3(b) and 7.2.2.3(c) identify the inspection decision points, requirements, development tasks, analyses and actions required to meet the damage tolerance requirements of a principal structural element (PSE). Figure 7.2.2.3(b) outlines the levels of damage tolerance requirements and can be used for test, analysis and maintenance planning. Figure 7.2.2.3(c) defines the flow of events and actions to be used to develop the data required for damage tolerance certification. The deterministic compliance method is based on a minimum of two sets of testing and analysis. The first set is designed to show positive margins of safety at design Ultimate Load with BVID size damages. This testing includes mostly coupons and subcomponents containing BVID. The second set of testing is designed to show positive margins of safety with large damage at design Limit Load. This testing in￾cludes subcomponent (e.g., five-stringer panels) and component structures with through the thickness damage, skin-stiffener debonds, large impact damages, etc. These types of damage are considered to be maximum design damage (MDD). Tests are used to show MDD-sized damage is easily detectable. Tests are also used to show MDD-sized damage and smaller will not grow under operational loads. Although this method meets FAA requirements for damage tolerance, it may not provide enough data to support the definition of accurate ADLs in structural repair manuals. Consequently, allowable damage sizes are conservatively set to smaller values. This has had the effect of increasing in-service repair costs of thin composite honeycomb sandwich panels in commercial aircraft

MIL-HDBK-17-3F Volume 3,Chapter 7-Damage Resistance,Durability,and Damage Tolerance Damage Type Requirements Is Damage Result of Yes Residual Strength In-Flight Discrete with "Get-Home"Loads Source Event per FAR 25.571(e) No Is Damage Yes Immediately Immediate Repair Obvious NO Residual Strength with Is Damage Yes Loads Between FAR Readily 25.571(b)and25.571(e) Detectable (see ACJ 25.571(a). Section 2.1.2) No Damage Growth Assessment Is Damage Yes Residual Strength for Inspection Planning to Detectable By with Loads per Ensure Detectable Damage Planned Does Not Drop Below CDT Inspections FAR25.571(b) During an Inspection Interval No Yes Does Undetectable Becomes Safe-Life Assessment Damage Yes Detectable per FAR 25.571(c) Grow No Residual Strength with Ultimate Loads FIGURE 7.2.2.3(b)Levels of damage tolerance assessments. The following are recommended approaches for developing data to support certification and to allow for reduced maintenance costs of composite aircraft structures: 1.The residual strength curve for each significant type of potential damage on each principal struc- tural element should be determined by analysis and/or test. 2.Characteristics describing the inspectability of the CDT as well as the type and extent of the damage should be documented to support maintenance planning activities. 3.For readily detectable damage,the magnitude of the threats that should be considered,similar to those in FAR 25.571(e).should include impact damage by ground vehicles and ground handing equipment,impact with jet gates,runway debris and thrown tire treads.Service experience has shown that damage associated with such events may persist for a few flights before the damage is detected and the structure repaired.The extent of damage that should be considered must be established by taking into account susceptibility to each type of accident. Structural damage design should be coupled with development of the aircraft maintenance plan in order to reduce in-service damage occurrences and repair costs.Test validation and analyses should address design ultimate strength,damage growth,residual strength,and maintenance issues for compos- ite structures.Independent studies of design Ultimate Load or Limit Load strength without data and analyses at intermediate load levels will not provide a balanced design that supports cost-effective main- 7-18

MIL-HDBK-17-3F Volume 3, Chapter 7 - Damage Resistance, Durability, and Damage Tolerance 7-18 Is Damage Result of In-Flight Discrete Source Event ? Is Damage Immediately Obvious ? Is Damage Readily Detectable ? Is Damage Detectable By Planned Inspections ? Does Undetectable Damage Grow ? Residual Strength with "Get-Home" Loads per FAR 25.571(e) Immediate Repair Residual Strength with Loads Between FAR 25.571(b) and 25.571(e) (see ACJ 25.571(a), Section 2.1.2) Residual Strength with Loads per FAR 25.571(b) Residual Strength with Ultimate Loads Safe-Life Assessment per FAR 25.571(c) Becomes Detectable ? Yes No Yes Yes No No Yes No Yes No Yes No Damage Growth Assessment for Inspection Planning to Ensure Detectable Damage Does Not Drop Below CDT During an Inspection Interval Damage Type Requirements FIGURE 7.2.2.3(b) Levels of damage tolerance assessments. The following are recommended approaches for developing data to support certification and to allow for reduced maintenance costs of composite aircraft structures: 1. The residual strength curve for each significant type of potential damage on each principal struc￾tural element should be determined by analysis and/or test. 2. Characteristics describing the inspectability of the CDT as well as the type and extent of the damage should be documented to support maintenance planning activities. 3. For readily detectable damage, the magnitude of the threats that should be considered, similar to those in FAR 25.571(e), should include impact damage by ground vehicles and ground handing equipment, impact with jet gates, runway debris and thrown tire treads. Service experience has shown that damage associated with such events may persist for a few flights before the damage is detected and the structure repaired. The extent of damage that should be considered must be established by taking into account susceptibility to each type of accident. Structural damage design should be coupled with development of the aircraft maintenance plan in order to reduce in-service damage occurrences and repair costs. Test validation and analyses should address design ultimate strength, damage growth, residual strength, and maintenance issues for compos￾ite structures. Independent studies of design Ultimate Load or Limit Load strength without data and analyses at intermediate load levels will not provide a balanced design that supports cost-effective main-

MIL-HDBK-17-3F Volume 3,Chapter 7-Damage Resistance,Durability,and Damage Tolerance tenance.For example,damage considered for ultimate strength analyses is more likely to occur in- service while the associated loads are very unlikely.The reverse is true for limit strength analyses.A da- tabase that covers a range of damage scenarios increasing in severity will allow for more cost-effective use of composite structures in commercial aircraft service. Part of Development Progra四 Select Component Define Damage Test Analysis Type Data Methods Residual Strength Select MDD,Determine "Curve" DLL Capability,Write DLL Margins for Damage Types Considered Validate Growth (or No-Growth) Characteristics of Determine CDT Maps for Component Using Damages Smaller Final Loads Than CDT Yes No Growth? Determine Damage Growth Rates Determine Inspection Determine Inspection Plan Based on Damage Plan Based on Accidental Growth Analysis Damage Rating.Environmenta Deterioration Rating and Maintenance Intervals FIGURE 7.2.2.3(c)Damage tolerance assessment flowchart for fail-safe loads. 7.2.2.4 Probabilistic or semi-probabilistic compliance methods(civil aviation) Probabilistic or semi-probabilistic methods consider first that the scheduled inspection program must account for damage severity.The use of these methods are acceptable for civil aviation as they comply with paragraph 7a(4)of the FAA Advisory Circular AC20 107A:"For the case of the no-growth concept, inspection intervals should be established as part of the maintenance program.In selecting such inter- vals,the residual strength associated with the assumed damages should be considered." In other words the larger the strength reduction is,the sooner the damage should be detected.Fur- thermore,these methods also consider that the need for inspection cannot disregard the likelihood of damage occurrence.The more likely the damage is,the sooner it should be detected.As a result,these 7-19

MIL-HDBK-17-3F Volume 3, Chapter 7 - Damage Resistance, Durability, and Damage Tolerance 7-19 tenance. For example, damage considered for ultimate strength analyses is more likely to occur in￾service while the associated loads are very unlikely. The reverse is true for limit strength analyses. A da￾tabase that covers a range of damage scenarios increasing in severity will allow for more cost-effective use of composite structures in commercial aircraft service. Select Component Select Component Define Damage Type Test Data Analysis Methods Residual Strength "Curve" Select MDD, Determine DLL Capability, Write DLL Margins for Damage Types Considered Select MDD, Determine DLL Capability, Write DLL Margins for Damage Types Considered Determine CDT Maps for Component Using Final Loads Determine CDT Maps for Component Using Final Loads Validate Growth (or No-Growth) Characteristics of Damages Smaller Than CDT Growth? Determine Inspection Plan Based on Accidental Damage Rating, Environmental Deterioration Rating and Maintenance Intervals Determine Inspection Plan Based on Accidental Damage Rating, Environmental Deterioration Rating and Maintenance Intervals Determine Damage Growth Rates Determine Inspection Plan Based on Damage Growth Analysis Determine Inspection Plan Based on Damage Growth Analysis Yes No Repeat for Each Damage Type Part of Development Program FIGURE 7.2.2.3(c) Damage tolerance assessment flowchart for fail-safe loads. 7.2.2.4 Probabilistic or semi-probabilistic compliance methods (civil aviation) Probabilistic or semi-probabilistic methods consider first that the scheduled inspection program must account for damage severity. The use of these methods are acceptable for civil aviation as they comply with paragraph 7a (4) of the FAA Advisory Circular AC20 107A: “For the case of the no-growth concept, inspection intervals should be established as part of the maintenance program. In selecting such inter￾vals, the residual strength associated with the assumed damages should be considered.” In other words the larger the strength reduction is, the sooner the damage should be detected. Fur￾thermore, these methods also consider that the need for inspection cannot disregard the likelihood of damage occurrence. The more likely the damage is, the sooner it should be detected. As a result, these

MIL-HDBK-17-3F Volume 3,Chapter 7-Damage Resistance,Durability,and Damage Tolerance methods depend on service data.Figure 7.2.2.4(a)illustrates how this "residual strength associated with the assumed damage"is governed by both the inspection interval and the damage probability. Strength capability Damage probability/unit of flight 10-9 10-5 103 Acceptable without inspection UL 、邈 Acceptable 1.4LL 曾 岩 目 which function of the Area 1.3LL Longer intervals Shorter intervals damage 1.2LL inspection where acceptability 1.1LL detected Not acceptable inter 8 Not acceptable,except the discrete source case [25 571 (e)] FIGURE 7.2.2.4(a)Illustration of probabilistic determination of acceptable residual strength levels Since these methods require some probabilistic input data,they are referred to as probabilistic or semi-probabilistic approaches.They were initially developed by Aerospatiale for certification of the ATR 72 outer wing,and later for the A330/340 ailerons.Subsequently a probabilistic approach was imple- mented by ALENIA for the ATR carbon tail. The basis of a probabilistic approach is to demonstrate that the inspection program will ensure that the combination of an occurrence of a load having "k x LL"intensity,with the presence of a "missed"acci- dental impact damage reducing the structure strength to"k x LL"load level,remains acceptable.The term "k x LL"refers to a factor times Limit Load.For primary structure catastrophic failure,this combination must be extremely remote(probability 10 per flight hour according to ACJ 25 1309).Higher probabili- ties can be accepted for less critical parts. Except for the case of hailstone impacts,load and damage occurrences can be considered as inde- pendent phenomena.Then it should be demonstrated that: Probabiltyo）◆Probabilitymissed damage）≤10'9 7.2.2.4(a) The following elements are contained in all probabilistic methodologies: 1.Perform a building block approach for deriving strength versus energy curves for all critical parts of the structure. 2.Investigate impact damage scenarios in order to derive the impact threat probability laws. 3. Demonstrate the no-growth concept of all damages up to VID threshold,in general through a full- scale fatigue test. 7-20

MIL-HDBK-17-3F Volume 3, Chapter 7 - Damage Resistance, Durability, and Damage Tolerance 7-20 methods depend on service data. Figure 7.2.2.4(a) illustrates how this “residual strength associated with the assumed damage” is governed by both the inspection interval and the damage probability. 10-9 10-3 10-5 Acceptable without inspection Not acceptable, except the discrete source case [§ 25 571 (e)] Longer intervals Shorter intervals Acceptable Not acceptable 1.1 LL 1.2 LL 1.3 LL 1.4 LL LL UL Area where acceptability is a function of the inspection interval at which damage is detected Area not taken into account in the certification Strength capability Damage probability/unit of flight FIGURE 7.2.2.4(a) Illustration of probabilistic determination of acceptable residual strength levels. Since these methods require some probabilistic input data, they are referred to as probabilistic or semi-probabilistic approaches. They were initially developed by Aerospatiale for certification of the ATR 72 outer wing, and later for the A330/340 ailerons. Subsequently a probabilistic approach was imple￾mented by ALENIA for the ATR carbon tail. The basis of a probabilistic approach is to demonstrate that the inspection program will ensure that the combination of an occurrence of a load having “k x LL” intensity, with the presence of a “missed” acci￾dental impact damage reducing the structure strength to “k x LL” load level, remains acceptable. The term “k x LL” refers to a factor times Limit Load. For primary structure catastrophic failure, this combination must be extremely remote (probability < 10-9 per flight hour according to ACJ 25 1309). Higher probabili￾ties can be accepted for less critical parts. Except for the case of hailstone impacts, load and damage occurrences can be considered as inde￾pendent phenomena. Then it should be demonstrated that: Probabilityload (k.LL) * Probabilitymissed damage (k.LL) < 10-9 7.2.2.4(a) The following elements are contained in all probabilistic methodologies: 1. Perform a building block approach for deriving strength versus energy curves for all critical parts of the structure. 2. Investigate impact damage scenarios in order to derive the impact threat probability laws. 3. Demonstrate the no-growth concept of all damages up to VID threshold, in general through a full￾scale fatigue test