MIL-HDBK-3F Volume 3,Chapter 4 Building Block Approach for Composite Structures 2 Verify or modify analysis methods which has been already verified at a lower level. 3 Allow inclusion of the defects in configured structure,which often do not take the same form in speci- mens and elements (e.g.,accidental damage caused by impact). This approach is based on the assumption that the structural/material response to applied load in test specimens with lower levels of complexity is directly transferable to specimens at higher levels of com- plexity.For example,fiber strength at the specimen level is the same as the fiber strength in the compo- nent.It is also implied that their variability is transferable upward.Thus,a statistical knockdown deter- mined from coupon tests (allowables)provides the same level of confidence at the structural component level. In a successful Building Block testing program,therefore,specimens can be designed so that failure modes at the lower level of structural complexity would be eliminated at the more complex specimens,by using verified design/analysis methods.Thus,the new failure modes at the next higher level of structural complexity can be isolated.The results of the more complex tests would be used to further modify/verify the analysis methods.Finally,an adequate analysis of methodology is verified and final design can be achieved. 4.3 METHODOLOGY In Section 4.1,Introduction and Philosophy,the Building Block Approach is introduced and the phi- losophical framework behind it are discussed,whereas,the Rationale and Assumptions in Section 4.2 provide a logical framework to guide the use of this approach while providing the key assumptions used. However,the Methodology used in performing a building block composite structure development program can spell success or failure in the effort.This section will discuss such Methodology,providing guidelines for its selection and use.The following discussion will present and discuss the methodology used in "building block composite structures development"for various vehicle applications.While there are some differences in methodology among these vehicle types,much of it is similar. 4.3.1 General approach The methodology used is shown in a generally logical,chronological order,but,during an actual vehi- cle "building block composite structure development"program,the start and completion of the methodol- ogy stages may overlap or not be in the order discussed herein.In such development programs in the real world,preliminary design/analysis of parts and elements and subcomponents may be accomplished using preliminary or estimated allowables.Element and/or subcomponent testing may be started or com- pleted before "design-to"allowables are available.But,"design-to"allowables should be completed be- fore full-scale component testing starts. The first step is to plan and initiate a suitable composite materials design allowables specimen test program on each composite material to be used.The number of material lots and the number of repli- cates required per type and environment will depend on whether the vehicle being developed is a proto- type,intermediate development(EMD),or production.In addition,the vehicle's structure criticality within its vehicle category (for instance,Aircraft,Spacecraft,Helicopter,Ground Vehicle,etc.)will affect the number of material lots and specimen replicates per test type and environment. The materials receiving inspection and acceptance requirements and the Materials Processes specification requirements will be a function of the structure criticality of the various parts of the selected vehicle.The number and kind of physical,mechanical,thermal,chemical,electrical and process proper- ties tests on the composite material will be a function of this structure criticality. The amount and level of quality assurance required on the test elements and subcomponents,as well as on the actual parts for the vehicle,is a function of the structure criticality of those parts and defect con- 4-5MIL-HDBK-3F Volume 3, Chapter 4 Building Block Approach for Composite Structures 4-5 2 Verify or modify analysis methods which has been already verified at a lower level. 3 Allow inclusion of the defects in configured structure, which often do not take the same form in speci￾mens and elements (e.g., accidental damage caused by impact). This approach is based on the assumption that the structural/material response to applied load in test specimens with lower levels of complexity is directly transferable to specimens at higher levels of com￾plexity. For example, fiber strength at the specimen level is the same as the fiber strength in the compo￾nent. It is also implied that their variability is transferable upward. Thus, a statistical knockdown deter￾mined from coupon tests (allowables) provides the same level of confidence at the structural component level. In a successful Building Block testing program, therefore, specimens can be designed so that failure modes at the lower level of structural complexity would be eliminated at the more complex specimens, by using verified design/analysis methods. Thus, the new failure modes at the next higher level of structural complexity can be isolated. The results of the more complex tests would be used to further modify/verify the analysis methods. Finally, an adequate analysis of methodology is verified and final design can be achieved. 4.3 METHODOLOGY In Section 4.1, Introduction and Philosophy, the Building Block Approach is introduced and the phi￾losophical framework behind it are discussed, whereas, the Rationale and Assumptions in Section 4.2 provide a logical framework to guide the use of this approach while providing the key assumptions used. However, the Methodology used in performing a building block composite structure development program can spell success or failure in the effort. This section will discuss such Methodology, providing guidelines for its selection and use. The following discussion will present and discuss the methodology used in “building block composite structures development” for various vehicle applications. While there are some differences in methodology among these vehicle types, much of it is similar. 4.3.1 General approach The methodology used is shown in a generally logical, chronological order, but, during an actual vehi￾cle “building block composite structure development” program, the start and completion of the methodol￾ogy stages may overlap or not be in the order discussed herein. In such development programs in the real world, preliminary design/analysis of parts and elements and subcomponents may be accomplished using preliminary or estimated allowables. Element and/or subcomponent testing may be started or com￾pleted before “design-to” allowables are available. But, “design-to” allowables should be completed be￾fore full-scale component testing starts. The first step is to plan and initiate a suitable composite materials design allowables specimen test program on each composite material to be used. The number of material lots and the number of repli￾cates required per type and environment will depend on whether the vehicle being developed is a proto￾type, intermediate development (EMD), or production. In addition, the vehicle’s structure criticality within its vehicle category (for instance, Aircraft, Spacecraft, Helicopter, Ground Vehicle, etc.) will affect the number of material lots and specimen replicates per test type and environment. The materials receiving inspection and acceptance requirements and the Materials & Processes specification requirements will be a function of the structure criticality of the various parts of the selected vehicle. The number and kind of physical, mechanical, thermal, chemical, electrical and process proper￾ties tests on the composite material will be a function of this structure criticality. The amount and level of quality assurance required on the test elements and subcomponents, as well as on the actual parts for the vehicle, is a function of the structure criticality of those parts and defect con-