MIL-HDBK-3F Volume 3,Chapter 4 Building Block Approach for Composite Structures 4.4.1.2 PMC composites building block structural development for DOD/NASA prototype aircraft Part B of the flowchart in Figure 4.4.1.1 defines the building block test effort in the general categories of: 1.Trade studies and concept development(element-single load path), 2.Selection,proof of concept,and analytical methods verification (sub-component-multiple load paths), 3. Structural verification and analytical methods improvement(contoured composite-multiple load path),and 4.Structural integrity and FEM validation(full-scale aircraft structure testing). The allowables shown in Figure 4.4.1.1 Part A and in Table 4.4.1.1 (a)logically flow into Part B,building block testing.Table 4.4.1.1(b)on physical defect requirements applies to both Parts A and B.The Part B building block test effort is delineated in Table 4.4.1.2(a)in accordance with the part's structural classifica- tion.The four categories,above,are defined in detail for each structural classification,with the higher the structural classification,the more testing and analysis required.The key point here is that these are guidelines for structural development testing.The actual structural testing needed for a specific classifica- tion of structure could be more or less,depending on the vehicle's mission and whether it is manned or unmanned.Knowing the structural part classification,the aircraft's purpose and mission,risk analysis can be applied to minimize testing cost and risk.FEM and closed form composite analysis methods utilizing proper mechanical and physical properties and allowables input data will be necessary every step of the way.Failure modes and loads(stresses)as well as strain and deflection readings must be monitored and correlated with predictions to assure low risk.The use of FEM or other analysis methods alone (without testing)or with inadequate testing that does not properly interrogate failure modes,stresses(strains),and deflections for comparison with predictions can create high risk situations that should not be tolerated. Another risk issue for composite structure is quality assurance (QA),a subject that applies to both Parts A and B.Table 4.4.1.2(b)presents the nominal QA requirements for the categories of 1.Material and process selection,screening,and material specification qualification, 2.Receiving inspection/acceptance testing, 3. In-process inspection, 4. Non-destructive inspection(NDI), 5. Destructive testing (DT),and 6. Traceability The QA requirements in each of these categories vary with the structural classification,with the higher the classification,the more quality assurance required.By following the procedure outlined in this table,the amount of QA necessary to keep risk at an acceptable level can be ascertained.Again the amount of QA needed and the risk taken will be a function of the aircraft type and mission and whether it is manned or unmanned.Risk and cost are inversely proportional to each other for composite structural parts in each classification,so the determination of acceptable risk is necessary to this building block test program for prototypes. 4-10MIL-HDBK-3F Volume 3, Chapter 4 Building Block Approach for Composite Structures 4-10 4.4.1.2 PMC composites building block structural development for DOD/NASA prototype aircraft Part B of the flowchart in Figure 4.4.1.1 defines the building block test effort in the general categories of: 1. Trade studies and concept development (element-single load path), 2. Selection, proof of concept, and analytical methods verification (sub-component-multiple load paths), 3. Structural verification and analytical methods improvement (contoured composite-multiple load path), and 4. Structural integrity and FEM validation (full-scale aircraft structure testing). The allowables shown in Figure 4.4.1.1 Part A and in Table 4.4.1.1 (a) logically flow into Part B, building block testing. Table 4.4.1.1(b) on physical defect requirements applies to both Parts A and B. The Part B building block test effort is delineated in Table 4.4.1.2(a) in accordance with the part's structural classifica￾tion. The four categories, above, are defined in detail for each structural classification, with the higher the structural classification, the more testing and analysis required. The key point here is that these are guidelines for structural development testing. The actual structural testing needed for a specific classifica￾tion of structure could be more or less, depending on the vehicle's mission and whether it is manned or unmanned. Knowing the structural part classification, the aircraft's purpose and mission, risk analysis can be applied to minimize testing cost and risk. FEM and closed form composite analysis methods utilizing proper mechanical and physical properties and allowables input data will be necessary every step of the way. Failure modes and loads (stresses) as well as strain and deflection readings must be monitored and correlated with predictions to assure low risk. The use of FEM or other analysis methods alone (without testing) or with inadequate testing that does not properly interrogate failure modes, stresses (strains), and deflections for comparison with predictions can create high risk situations that should not be tolerated. Another risk issue for composite structure is quality assurance (QA), a subject that applies to both Parts A and B. Table 4.4.1.2(b) presents the nominal QA requirements for the categories of 1. Material and process selection, screening, and material specification qualification, 2. Receiving inspection/acceptance testing, 3. In-process inspection, 4. Non-destructive inspection (NDI), 5. Destructive testing (DT), and 6. Traceability The QA requirements in each of these categories vary with the structural classification, with the higher the classification, the more quality assurance required. By following the procedure outlined in this table, the amount of QA necessary to keep risk at an acceptable level can be ascertained. Again the amount of QA needed and the risk taken will be a function of the aircraft type and mission and whether it is manned or unmanned. Risk and cost are inversely proportional to each other for composite structural parts in each classification, so the determination of acceptable risk is necessary to this building block test program for prototypes