MIL-HDBK-3F Volume 3,Chapter 4 Building Block Approach for Composite Structures siderations for structural substantiation and maintenance.In addition the type of tests selected,the num- ber of replicates,and instrumentation needed is a function of the part's structure criticality. Customer requirements and costs as well as safety and durability concerns may dictate the full scale testing requirements in addition to analytical prediction verification.Such full-scale testing could be proof loading to critical design limit load at RTD conditions,proof loading at various environmental conditions, static test to Design Limit Load (DLL)and Design Ultimate Load(DUL)at RT with or without load en- hancement factors to simulate elevated temperatures,and of course static loading to failure,in some cases.In addition,damage tolerance testing is often required to ensure safety for flight critical structure. Durability(fatigue)testing is sometimes required in severe environments and may be required to prove- out long term acceptable economic lifetimes. The individual methodologies discussed above are,in many cases,available within the companies doing the development work,or,are readily available at a specialty subcontractor.It is usually a matter of organizing such methodologies in a rational manner to achieve an acceptable vehicle composite structure building block development program.Such methodologies are defined and organized in more detail in the individual vehicle type subsections listed below. 4.4 CONSIDERATIONS FOR SPECIFIC APPLICATIONS 4.4.1 Aircraft for prototypes A detailed description of the allowables and building block test effort needed for acceptable risk and cost effective DOD/NASA prototype composite aircraft structure is presented in the following sections Section 4.4.1.1 presents the PMC composite allowables generation for DOD/NASA prototype aircraft structure.In Section 4.4.1.2,the PMC composites building block structural development for DOD/NASA prototype aircraft is detailed.And,finally,a summary of allowables and building block test efforts for DOD/NASA prototype composite aircraft structure is given in Section 4.4.1.3. 4.4.1.1 PMC composite allowables generation for DOD/NASA prototype aircraft structure Allowables generation is needed to support the building block test program depicted in Figure 4.4.1.1, Part A consists of five steps: 1.Experimentally generate ply level static strength and stiffness properties including the testing of 0 or 1-axis tension and compression,90 or 2-axis tension and compression and 0or 12-axis in-plane shear specimens with stress/strain curves utilizing,to the extent possible,ASTM D 3039, D3410,andD3518. 2.Experimentally generate quasi-isotropic laminate level,static strength and stiffness properties in- cluding the testing of x-axis plain and open hole tension,compression,and in-plane shear speci- mens and tension and compression loaded double shear bearing specimens per ASTM D 3039 for tension and compression and bearing specimens per other standards,respectively,that are currently under development in the ASTM D-30 Committee. 3.The test data generated will be reduced,statistically,to obtain allowable type values using the B-basis value(90%probability,95%confidence)approach or the 85%of mean value approach if the test scatter is too high.The higher of the two values should be used.This approach was first presented by Grimes in Reference 4.4.1.1. 4.Develop input ply allowables for use in analytical methods that are used in design/analysis.In general the lower of the ultimate or 1.5 x yield strength reduced value should be used for tension, compression,and in-plane shear strength critical allowables.When in-plane shear strength is not critical the reduced ultimate shear strength(a high value)should be used. 4-6MIL-HDBK-3F Volume 3, Chapter 4 Building Block Approach for Composite Structures 4-6 siderations for structural substantiation and maintenance. In addition the type of tests selected, the num￾ber of replicates, and instrumentation needed is a function of the part’s structure criticality. Customer requirements and costs as well as safety and durability concerns may dictate the full scale testing requirements in addition to analytical prediction verification. Such full-scale testing could be proof loading to critical design limit load at RTD conditions, proof loading at various environmental conditions, static test to Design Limit Load (DLL) and Design Ultimate Load (DUL) at RT with or without load en￾hancement factors to simulate elevated temperatures, and of course static loading to failure, in some cases. In addition, damage tolerance testing is often required to ensure safety for flight critical structure. Durability (fatigue) testing is sometimes required in severe environments and may be required to prove￾out long term acceptable economic lifetimes. The individual methodologies discussed above are, in many cases, available within the companies doing the development work, or, are readily available at a specialty subcontractor. It is usually a matter of organizing such methodologies in a rational manner to achieve an acceptable vehicle composite structure building block development program. Such methodologies are defined and organized in more detail in the individual vehicle type subsections listed below. 4.4 CONSIDERATIONS FOR SPECIFIC APPLICATIONS 4.4.1 Aircraft for prototypes A detailed description of the allowables and building block test effort needed for acceptable risk and cost effective DOD/NASA prototype composite aircraft structure is presented in the following sections. Section 4.4.1.1 presents the PMC composite allowables generation for DOD/NASA prototype aircraft structure. In Section 4.4.1.2, the PMC composites building block structural development for DOD/NASA prototype aircraft is detailed. And, finally, a summary of allowables and building block test efforts for DOD/NASA prototype composite aircraft structure is given in Section 4.4.1.3. 4.4.1.1 PMC composite allowables generation for DOD/NASA prototype aircraft structure Allowables generation is needed to support the building block test program depicted in Figure 4.4.1.1, Part A consists of five steps: 1. Experimentally generate ply level static strength and stiffness properties including the testing of 0° or 1-axis tension and compression, 90° or 2-axis tension and compression and 0° or 12-axis in-plane shear specimens with stress/strain curves utilizing, to the extent possible, ASTM D 3039, D 3410, and D 3518. 2. Experimentally generate quasi-isotropic laminate level, static strength and stiffness properties in￾cluding the testing of x-axis plain and open hole tension, compression, and in-plane shear speci￾mens and tension and compression loaded double shear bearing specimens per ASTM D 3039 for tension and compression and bearing specimens per other standards, respectively, that are currently under development in the ASTM D-30 Committee. 3. The test data generated will be reduced, statistically, to obtain allowable type values using the B-basis value (90% probability, 95% confidence) approach or the 85% of mean value approach if the test scatter is too high. The higher of the two values should be used. This approach was first presented by Grimes in Reference 4.4.1.1. 4. Develop input ply allowables for use in analytical methods that are used in design/analysis. In general the lower of the ultimate or 1.5 x yield strength reduced value should be used for tension, compression, and in-plane shear strength critical allowables. When in-plane shear strength is not critical the reduced ultimate shear strength (a high value) should be used