《纺织复合材料》课程参考文献（Composite Materials Handbook，Volume 1）CHAPTER 2 GUIDELINES FOR PROPERTY TESTING OF COMPOSITES

MIL-HDBK-17-1F Volume 1,Chapter 2 Guidelines for Property Testing of Composites CHAPTER 2 GUIDELINES FOR PROPERTY TESTING OF COMPOSITES 2.1 INTRODUCTION This chapter provides guidelines for the experimental characterization of polymer matrix composites and documents the requirements for publishing material property data in MIL-HDBK-17.Recommended test matrices for a number of uses are presented and discussed.Potential problem areas in testing and test matrix planning are highlighted and helpful options are provided.The chapter sections cover the fol- lowing: Section 2.1 introduces the chapter and presents an approach to categorizing testing needs Section 2.2 discusses a wide variety of factors that affect test results and basis values,focusing on issues of particular importance during test planning,whether for a single test or for a large testing program requiring the evaluation of hundreds or thousands of test specimens. Section 2.3 presents a number of preplanned test matrices organized by the key categories intro- duced in Section 2.1,covering the characterization of specific sets of properties at recommended test environments,and including requirements for batch and specimen quantities. Section 2.4 describes procedures for normalizing,reducing,and reporting test data Section 2.5 describes detailed test population sampling requirements,and specific test data nor- malization and documentation requirements for inclusion of data into MIL-HDBK-17 Volume 2. 2.1.1 Building-block approach to substantiation of composite structures Analysis alone is generally not considered adequate for substantiation of composite structural de- signs.Instead,the "building-block approach"to design development testing is used in concert with analy- sis.This approach is often considered essential to the qualification/certification'of composite structures due to the sensitivity of composites to out-of-plane loads,the multiplicity of composite failure modes and the lack of standard analytical methods. The building-block approach is also used to establish environmental compensation values applied to full-scale tests at room-temperature ambient environment,as it is often impractical to conduct these tests under the actual moisture and temperature environment.Lower-level tests justify these environmental compensation factors.Similarly,other building-block tests determine truncation approaches for fatigue spectra and compensation for fatigue scatter at the full-scale level. The building-block approach is shown schematically in Figure 2.1.1 and discussed in detail in Refer- ences 2.1.1(b)and(c).The approach can be summarized in the following steps: 1.Generate material basis values and preliminary design allowables. 2.Based on the design/analysis of the structure,select critical areas for subsequent test verification. 3.Determine the most strength-critical failure mode for each design feature. 4. Select the test environment that will produce the strength-critical failure mode.Special attention should be given to matrix-sensitive failure modes (such as compression,out-of-plane shear,and bondlines)and potential "hot-spots"caused by out-of-plane loads or stiffness tailored designs. 5. Design and test a series of test specimens,each one of which simulates a single selected failure mode and loading condition,compare to analytical predictions,and adjust analysis models or de- sign allowables as necessary. 6. Design and conduct increasingly more complicated tests that evaluate more complicated loading situations with the possibility of failure from several potential failure modes.Compare to analyti- cal predictions and adjust analysis models as necessary. Design substantiation is often called"qualification"in U.S.DOD applications and "certification"in civilian applications involving the U.S.FAA.All three terms describe a similar process,but "substantiation"can be considered the more generic temm,with "qualifica- tion"and "certification"often limited to the foregoing more restricted senses. 2-1

MIL-HDBK-17-1F Volume 1, Chapter 2 Guidelines for Property Testing of Composites 2-1 CHAPTER 2 GUIDELINES FOR PROPERTY TESTING OF COMPOSITES 2.1 INTRODUCTION This chapter provides guidelines for the experimental characterization of polymer matrix composites and documents the requirements for publishing material property data in MIL-HDBK-17. Recommended test matrices for a number of uses are presented and discussed. Potential problem areas in testing and test matrix planning are highlighted and helpful options are provided. The chapter sections cover the fol￾lowing: • Section 2.1 introduces the chapter and presents an approach to categorizing testing needs. • Section 2.2 discusses a wide variety of factors that affect test results and basis values, focusing on issues of particular importance during test planning, whether for a single test or for a large testing program requiring the evaluation of hundreds or thousands of test specimens. • Section 2.3 presents a number of preplanned test matrices organized by the key categories intro￾duced in Section 2.1, covering the characterization of specific sets of properties at recommended test environments, and including requirements for batch and specimen quantities. • Section 2.4 describes procedures for normalizing, reducing, and reporting test data. • Section 2.5 describes detailed test population sampling requirements, and specific test data nor￾malization and documentation requirements for inclusion of data into MIL-HDBK-17 Volume 2. 2.1.1 Building-block approach to substantiation of composite structures Analysis alone is generally not considered adequate for substantiation of composite structural de￾signs. Instead, the "building-block approach" to design development testing is used in concert with analy￾sis. This approach is often considered essential to the qualification/certification1 of composite structures due to the sensitivity of composites to out-of-plane loads, the multiplicity of composite failure modes and the lack of standard analytical methods. The building-block approach is also used to establish environmental compensation values applied to full-scale tests at room-temperature ambient environment, as it is often impractical to conduct these tests under the actual moisture and temperature environment. Lower-level tests justify these environmental compensation factors. Similarly, other building-block tests determine truncation approaches for fatigue spectra and compensation for fatigue scatter at the full-scale level. The building-block approach is shown schematically in Figure 2.1.1 and discussed in detail in Refer￾ences 2.1.1(b) and (c). The approach can be summarized in the following steps: 1. Generate material basis values and preliminary design allowables. 2. Based on the design/analysis of the structure, select critical areas for subsequent test verification. 3. Determine the most strength-critical failure mode for each design feature. 4. Select the test environment that will produce the strength-critical failure mode. Special attention should be given to matrix-sensitive failure modes (such as compression, out-of-plane shear, and bondlines) and potential "hot-spots" caused by out-of-plane loads or stiffness tailored designs. 5. Design and test a series of test specimens, each one of which simulates a single selected failure mode and loading condition, compare to analytical predictions, and adjust analysis models or de￾sign allowables as necessary. 6. Design and conduct increasingly more complicated tests that evaluate more complicated loading situations with the possibility of failure from several potential failure modes. Compare to analyti￾cal predictions and adjust analysis models as necessary. 1 Design substantiation is often called "qualification" in U.S. DOD applications and "certification" in civilian applications involving the U.S. FAA. All three terms describe a similar process, but "substantiation" can be considered the more generic term, with "qualifica￾tion" and "certification" often limited to the foregoing more restricted senses

MIL-HDBK-17-1F Volume 1,Chapter 2 Guidelines for Property Testing of Composites 7.Design (including compensation factors)and conduct,as required,full-scale component static and fatigue testing for final validation of internal loads and structural integrity.Compare to analy- SiS. COMPONENTS SUB-COMPONENTS STRUCTURAL FEATURES DETAILS ELEMENTS 88☐ COUPONS 卧理 DATA BASE 0 ⅢⅢ22☒ FIGURE 2.1.1 The pyramid of tests(Reference 2.1.1(a)). 2.1.2 Test levels and data uses Testing activities can be defined in two basic ways,Structural Complexity Level and Data Application Category.The classes within each are discussed in more detail in the sections that follow,and can be used to map large-scale testing programs as an aid to test planning,as illustrated in Section 2.1.2.3. 2.1.2.1 Structural complexity levels The five Structural Complexity Levels'are each geometry or form-based:constituent,lamina,lami- nate,structural element,and structural subcomponent.The material form(s)to be tested,and the relative emphasis placed on each level,should be determined early in the material data development planning process,and will likely depend upon many factors,including:manufacturing process,structural applica- tion,corporate/organizational practices,and/or the procurement or certification agency.While a single level may suffice in rare instances,most applications will require at least two levels,and it is common to use all five in a complete implementation of the building-block approach.Regardless of the Structural Complexity Level selected,physical and chemical property characterization of the prepreg(or the matrix, Due to the popularity of lamina-level testing and analysis,discussions in this handbook often emphasize development of a lamina- level database;however,this is not intended to inhibit use of any of the other Structural Complexity Levels,either singly or in combi- nation.Also,this handbook does not emphasize the structural subcomponent category since it is so strongly application dependent: however,many of the test planning and data documentation concepts for coupon testing contained herein can be extended to struc- tural subcomponent(or higher)testing. 2-2

MIL-HDBK-17-1F Volume 1, Chapter 2 Guidelines for Property Testing of Composites 2-2 7. Design (including compensation factors) and conduct, as required, full-scale component static and fatigue testing for final validation of internal loads and structural integrity. Compare to analy￾sis. FIGURE 2.1.1 The pyramid of tests (Reference 2.1.1(a)). 2.1.2 Test levels and data uses Testing activities can be defined in two basic ways, Structural Complexity Level and Data Application Category. The classes within each are discussed in more detail in the sections that follow, and can be used to map large-scale testing programs as an aid to test planning, as illustrated in Section 2.1.2.3. 2.1.2.1 Structural complexity levels The five Structural Complexity Levels1 are each geometry or form-based: constituent, lamina, lami￾nate, structural element, and structural subcomponent. The material form(s) to be tested, and the relative emphasis placed on each level, should be determined early in the material data development planning process, and will likely depend upon many factors, including: manufacturing process, structural applica￾tion, corporate/organizational practices, and/or the procurement or certification agency. While a single level may suffice in rare instances, most applications will require at least two levels, and it is common to use all five in a complete implementation of the building-block approach. Regardless of the Structural Complexity Level selected, physical and chemical property characterization of the prepreg (or the matrix, 1 Due to the popularity of lamina-level testing and analysis, discussions in this handbook often emphasize development of a lamina￾level database; however, this is not intended to inhibit use of any of the other Structural Complexity Levels, either singly or in combi￾nation. Also, this handbook does not emphasize the structural subcomponent category since it is so strongly application dependent; however, many of the test planning and data documentation concepts for coupon testing contained herein can be extended to struc￾tural subcomponent (or higher) testing

MIL-HDBK-17-1F Volume 1,Chapter 2 Guidelines for Property Testing of Composites if it is added as part of the process,as with resin transfer molding)is necessary to support physical and mechanical property test results.Each procurement or certification agency has specific minimum re- quirements and guidelines for use of data.Users of MIL-HDBK-17 are advised to coordinate with the procuring or certifying agency before planning and conducting any testing that supports structural qualifi- cation or certification. The five Structural Complexity Levels cover the following areas: Constituent Testing: This evaluates the individual properties of fibers,fiber forms,matrix materials,and fiber-matrix pre- forms.Key properties,for example,include fiber and matrix density,and fiber tensile strength and tensile modulus. Lamina Testing: This evaluates the properties of the fiber and matrix together in the composite material form.For the purpose of this discussion prepreg properties are included in this level,although they are sometimes bro- ken-out into a separate level.Key properties include fiber areal weight,matrix content,void content, cured ply thickness,lamina tensile strengths and moduli,lamina compressive strengths and moduli,and lamina shear strengths and moduli. Laminate Testing: Laminate testing characterizes the response of the composite material in a given laminate design. Key properties include tensile strengths and moduli,compressive strengths and moduli,shear strengths and moduli,interlaminar fracture toughness,and fatigue resistance. Structural Element Testing: This evaluates the ability of the material to tolerate common laminate discontinuities.Key properties include open and filled hole tensile strengths,open and filled hole compressive strengths,compression after impact strength,and joint bearing and bearing bypass strengths. Structural Subcomponent(or higher)Testing: This testing evaluates the behavior and failure mode of increasingly more complex structural assem- blies.These are application specific and not specifically covered by MIL-HDBK-17. 2.1.2.2 Data application categories Material property testing can also be grouped by data application into one or more of the following five categories:screening,'qualification,acceptance,equivalence,and structural substantiation.The starting point for testing most material systems is usually material screening.Material systems intended for use in engineering hardware are subjected to further testing to obtain additional data.While structural substantiation requirements,the last category,are not specifically addressed by MIL-HDBK-17 data gen- erated in accordance with MIL-HDBK-17 guidelines may form part of these requirements.The five Data Application Categories cover the following areas: Screening Testing. This is the assessment of material candidates for a given application,often with a given application in mind.The purpose of screening testing is initial evaluation of new material systems under worst-case environmental and loading test conditions.This handbook provides guidelines for screening new material systems based on key properties for aerospace structural applications.The MIL-HDBK-17 screening test matrix provides average values for various strength,moduli,and physical properties,includes both lamina A more limited form of screening testing for the characteristic response of a limited number of specific properties(often only one property)is not explicitly named as a testing category,but is commonly performed.Such limited testing usually consists of small test populations of three to six,usually from a single material batch,and often focuses on a specific environmental condition.As each instance of testing of this type has a specific but widely varying purpose MIL-HDBK-17 does not provide explicit test matrix recommendations;however,the guidance provided for the remaining testing categories remains a useful reference for test planning. 2-3

MIL-HDBK-17-1F Volume 1, Chapter 2 Guidelines for Property Testing of Composites 2-3 if it is added as part of the process, as with resin transfer molding) is necessary to support physical and mechanical property test results. Each procurement or certification agency has specific minimum re￾quirements and guidelines for use of data. Users of MIL-HDBK-17 are advised to coordinate with the procuring or certifying agency before planning and conducting any testing that supports structural qualifi￾cation or certification. The five Structural Complexity Levels cover the following areas: Constituent Testing: This evaluates the individual properties of fibers, fiber forms, matrix materials, and fiber-matrix pre￾forms. Key properties, for example, include fiber and matrix density, and fiber tensile strength and tensile modulus. Lamina Testing: This evaluates the properties of the fiber and matrix together in the composite material form. For the purpose of this discussion prepreg properties are included in this level, although they are sometimes bro￾ken-out into a separate level. Key properties include fiber areal weight, matrix content, void content, cured ply thickness, lamina tensile strengths and moduli, lamina compressive strengths and moduli, and lamina shear strengths and moduli. Laminate Testing: Laminate testing characterizes the response of the composite material in a given laminate design. Key properties include tensile strengths and moduli, compressive strengths and moduli, shear strengths and moduli, interlaminar fracture toughness, and fatigue resistance. Structural Element Testing: This evaluates the ability of the material to tolerate common laminate discontinuities. Key properties include open and filled hole tensile strengths, open and filled hole compressive strengths, compression after impact strength, and joint bearing and bearing bypass strengths. Structural Subcomponent (or higher) Testing: This testing evaluates the behavior and failure mode of increasingly more complex structural assem￾blies. These are application specific and not specifically covered by MIL-HDBK-17. 2.1.2.2 Data application categories Material property testing can also be grouped by data application into one or more of the following five categories: screening,1 qualification, acceptance, equivalence, and structural substantiation. The starting point for testing most material systems is usually material screening. Material systems intended for use in engineering hardware are subjected to further testing to obtain additional data. While structural substantiation requirements, the last category, are not specifically addressed by MIL-HDBK-17 data gen￾erated in accordance with MIL-HDBK-17 guidelines may form part of these requirements. The five Data Application Categories cover the following areas: Screening Testing: This is the assessment of material candidates for a given application, often with a given application in mind. The purpose of screening testing is initial evaluation of new material systems under worst-case environmental and loading test conditions. This handbook provides guidelines for screening new material systems based on key properties for aerospace structural applications. The MIL-HDBK-17 screening test matrix provides average values for various strength, moduli, and physical properties, includes both lamina 1 A more limited form of screening testing for the characteristic response of a limited number of specific properties (often only one property) is not explicitly named as a testing category, but is commonly performed. Such limited testing usually consists of small test populations of three to six, usually from a single material batch, and often focuses on a specific environmental condition. As each instance of testing of this type has a specific but widely varying purpose MIL-HDBK-17 does not provide explicit test matrix recommendations; however, the guidance provided for the remaining testing categories remains a useful reference for test planning

MIL-HDBK-17-1F Volume 1,Chapter 2 Guidelines for Property Testing of Composites and laminate level testing,and is designed both to eliminate deficient material systems from the material selection process and to reveal promising new material systems before planning subsequent,more in- depth,evaluations. Material Qualification Testing: This step proves the ability of a given material/process to meet the requirements of a material specifi- cation;it is also the process of establishing the original specification requirement values.Rigorous mate- rial qualification testing considers the statistics of the data and is ideally a subset of,or directly related to. the design allowables testing performed to satisfy structural substantiation requirements.(However,while a material may be qualified to a given specification,it still must be approved for use in each specific appli- cation.)The objective is quantitative assessment of the variability of key material properties,leading to various statistics that are used to establish material acceptance,equivalence,quality control,and design basis values.Since there are various sampling and statistical approaches used within the industry,the approach used must be explicitly defined.While a generic basis value can be obtained many ways,a MIL-HDBK-17 basis value carries with it well-defined sampling requirements and a specific statistical de- termination process,and emphasizes additional considerations like test methodology,failure mode,and data documentation. Acceptance Testing: This is the task of verifying material consistency through periodic sampling of material product and evaluation of key material properties.Test results from small sample sizes are statistically compared with control values established from prior testing to determine whether or not the material production process has changed significantly. Equivalence Testing: This task assesses the equivalence of an alternate material to a previously characterized material often for the purpose of utilizing an existing material property database.The objective is evaluation of key properties for test populations large enough to provide a definitive conclusion,but small enough to pro- vide significant cost savings as compared to generating an entirely new database.A significant use in- cludes evaluation of possible second-sources of supply for a previously qualified material.However,the most common uses for this process are:1)evaluation of minor constituent,constituent processing,or fab- rication processing changes for a qualified material system,and 2)substantiation of previously estab- lished MIL-HDBK-17 basis values. Structural Substantiation Testing: This is the process of assessing the ability of a given structure to meet the requirements of a specific application.The development of design allowables,ideally derived or related to material basis values obtained during a material qualification task,is considered a part of this effort.When performed for the U.S.DOD this task is called structural qualification,and when the U.S.FAA is the certifying agency it is called structural certification 2.1.2.3 Test program definition A matrix is shown in Table 2.1.2.3 that can be used in test planning for large-scale testing programs. The material property tests from the Structural Complexity Levels and Data Application Categories are listed on the axes of an array,with each intersecting cell describing a distinct testing activity(though cer- tain combinations will rarely be used).Groups of cells can be used to summarize the scope of entire building-block testing programs.The array shown in Table 2.1.2.3 illustrates a common(but by no means universal)testing sequence in the substantiation of a composite-based aerospace structural application. The sequence begins with the hatched cells at the upper left of the array and proceeds,with time,toward the cells at the lower right,with the numbered notes indicating the approximate order in the sequence. (The structural substantiation category and structural subcomponent level are shaded to indicated that they are not specifically addressed by MIL-HDBK-17). 2-4

MIL-HDBK-17-1F Volume 1, Chapter 2 Guidelines for Property Testing of Composites 2-4 and laminate level testing, and is designed both to eliminate deficient material systems from the material selection process and to reveal promising new material systems before planning subsequent, more in￾depth, evaluations. Material Qualification Testing: This step proves the ability of a given material/process to meet the requirements of a material specifi￾cation; it is also the process of establishing the original specification requirement values. Rigorous mate￾rial qualification testing considers the statistics of the data and is ideally a subset of, or directly related to, the design allowables testing performed to satisfy structural substantiation requirements. (However, while a material may be qualified to a given specification, it still must be approved for use in each specific appli￾cation.) The objective is quantitative assessment of the variability of key material properties, leading to various statistics that are used to establish material acceptance, equivalence, quality control, and design basis values. Since there are various sampling and statistical approaches used within the industry, the approach used must be explicitly defined. While a generic basis value can be obtained many ways, a MIL-HDBK-17 basis value carries with it well-defined sampling requirements and a specific statistical de￾termination process, and emphasizes additional considerations like test methodology, failure mode, and data documentation. Acceptance Testing: This is the task of verifying material consistency through periodic sampling of material product and evaluation of key material properties. Test results from small sample sizes are statistically compared with control values established from prior testing to determine whether or not the material production process has changed significantly. Equivalence Testing: This task assesses the equivalence of an alternate material to a previously characterized material, often for the purpose of utilizing an existing material property database. The objective is evaluation of key properties for test populations large enough to provide a definitive conclusion, but small enough to pro￾vide significant cost savings as compared to generating an entirely new database. A significant use in￾cludes evaluation of possible second-sources of supply for a previously qualified material. However, the most common uses for this process are: 1) evaluation of minor constituent, constituent processing, or fab￾rication processing changes for a qualified material system, and 2) substantiation of previously estab￾lished MIL-HDBK-17 basis values. Structural Substantiation Testing: This is the process of assessing the ability of a given structure to meet the requirements of a specific application. The development of design allowables, ideally derived or related to material basis values obtained during a material qualification task, is considered a part of this effort. When performed for the U.S. DOD this task is called structural qualification, and when the U.S. FAA is the certifying agency it is called structural certification. 2.1.2.3 Test program definition A matrix is shown in Table 2.1.2.3 that can be used in test planning for large-scale testing programs. The material property tests from the Structural Complexity Levels and Data Application Categories are listed on the axes of an array, with each intersecting cell describing a distinct testing activity (though cer￾tain combinations will rarely be used). Groups of cells can be used to summarize the scope of entire building-block testing programs. The array shown in Table 2.1.2.3 illustrates a common (but by no means universal) testing sequence in the substantiation of a composite-based aerospace structural application. The sequence begins with the hatched cells at the upper left of the array and proceeds, with time, toward the cells at the lower right, with the numbered notes indicating the approximate order in the sequence. (The structural substantiation category and structural subcomponent level are shaded to indicated that they are not specifically addressed by MIL-HDBK-17)

MIL-HDBK-17-1F Volume 1,Chapter 2 Guidelines for Property Testing of Composites TABLE 2.1.2.3 Test program definition. STRUCTURAL COMPLEXITY DATA APPLICATION CATEGORIES LEVEL Material Material Material Material Structural Screening Qualification Acceptance Equivalence Substantiation Constituent 1 Lamina 4 Laminate Structural 3 Element Structural 9 Subcomponent This handbook defines a number of recommended test matrices in Section 2.3.organized by Data Application Category. 2.2 TEST PROGRAM PLANNING 2.2.1 Overview Section 2.2 discusses a number of testing objectives that affect the execution of testing programs. The next section,2.3 on Recommended Test Matrices,completes these items by providing recommended test matrices(types of tests and test quantities at various environments)for a number of composite mate- rial forms and objectives.These pre-defined test matrices may hove to be customized for use with a spe- cific application. Characterization of composite material properties is distinctly different than for either metals or unrein- forced plastics.Section 2.2 provides information on many of the critical differences that affect testing and test planning,including: ·testing matrices. material sampling and pooling issues, statistical calculations, ● test method selection. material and processing variation. conditioning and non-ambient testing issues, alternative coupon confiqurations, data normalization and documentation,and application-specific testing. All significant testing programs should begin with preparation of a detailed test plan document.A test plan specifies material properties to be evaluated,selects tests methods,eliminates options offered by 2-5

MIL-HDBK-17-1F Volume 1, Chapter 2 Guidelines for Property Testing of Composites 2-5 TABLE 2.1.2.3 Test program definition. STRUCTURAL COMPLEXITY LEVEL DATA APPLICATION CATEGORIES Material Screening Material Qualification Material Acceptance Material Equivalence Structural Substantiation Constituent 1 - - - - Lamina 2 4 - - Laminate - 5 - 7 Structural Element 3 6 - 8 Structural Subcomponent - - - - 9 This handbook defines a number of recommended test matrices in Section 2.3, organized by Data Application Category. 2.2 TEST PROGRAM PLANNING 2.2.1 Overview Section 2.2 discusses a number of testing objectives that affect the execution of testing programs. The next section, 2.3 on Recommended Test Matrices, completes these items by providing recommended test matrices (types of tests and test quantities at various environments) for a number of composite mate￾rial forms and objectives. These pre-defined test matrices may hove to be customized for use with a spe￾cific application. Characterization of composite material properties is distinctly different than for either metals or unrein￾forced plastics. Section 2.2 provides information on many of the critical differences that affect testing and test planning, including: • testing matrices, • material sampling and pooling issues, • statistical calculations, • test method selection, • material and processing variation, • conditioning and non-ambient testing issues, • alternative coupon configurations, • data normalization and documentation, and • application-specific testing. All significant testing programs should begin with preparation of a detailed test plan document. A test plan specifies material properties to be evaluated, selects tests methods, eliminates options offered by