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. 2-1MIL-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