FAA/NASA/Industry Review of Key Characteristics for Composite Material Control

1. FAA/NASA/Industry Review of Key Characteristics for Composite Material Control Mark Chris, Principal Engineer Bell Helicopter Textron Composite M&P / Structures DER Experience/Responsibilities: • Write/revise material and process specifications. • Plan & execute basic material qualification programs. • Plan & execute laminate point design allowable programs. • Provide allowables with analysis methodology to Design Groups. • Review & Approval of manufacturing planning and engineering drawings. • DER support for Bell Commercial Models 204/5, 212, 214, 412 & BA609. • Engineering support for Bell Military Models 406, Huey, Cobra & V-22. • Composite production & repair process development & troubleshooting. • Composite material & process related research.

2. FAA/NASA/Industry Process Specification Guidelines 5.3.2 Required Materials • In depth discussion of purchaser and supplier batch certification testing should be summarized with reference to see “Guidelines for Material Specification” document for a detailed discussion. Process Specifications are generally limited to a general statement such as: “All prepreg materials processed in accordance with this specification shall be certified to meet the requirements of the applicable material specification.” • In depth discussion of storage conditions, handling life and out-time life should be summarized with a reference to see “Guidelines for Material Specification” for detailed discussion. Process Specifications are generally limited to a general statement such as: “All prepreg materials processed in accordance with this specification shall be within their required storage life, handling life and out-time life.” • Discussion of controlled clean room environment (temperature, humidity, particulate count) and its importance to part quality is already addressed under paragraph 5.3.4 Facilities.

3. FAA/NASA/Industry Process Specification Guidelines Add Minimum Recommended List of Items to be defined on Engineering Drawing (and/or qualification test plan) Engineering Drawing Call-out. The engineering drawing shall specify: a. Material procurement specification, type, class, form and grade of composite and adhesive material. b. Number of plies of composite material and/or adhesive material. c. The orientation of each ply of composite material. d. The type of adhesive film to bond cured and uncured laminates. e. Complete part mechanical property verification tests using process verification test coupons, assembly cutoffs, or sacrifice parts, if applicable. f. Visual, ultrasonic, radiographic, or other non-destructive inspection. g. Acceptance and rejection criteria for porosity, voids, delaminations, etc., in the cured composite laminate shall be in accordance with XXX. Any special acceptance criteria shall be defined on the drawing.

4. FAA/NASA/Industry Process Specification Guidelines General Comments • Add information to Table 5, “Tooling Control List” to address (a) tool thermal survey and (b) calibration of tool mounted sensors. • Add information to address how to handle vacuum bag leaks that occur during cure with specific criteria.

5. FAA/NASA/IndustryMaterial Specification Guidelines • General Comments: • Consider adding more specific definitions of storage life, handling life and mechanical life with an accompanying figure. Clock should start at “date of manufacture” to be further defined as “date of impregnation”. For example: Date of Manufacture

6. Optional Laminate Tension Properties-Determine Critical Hole Condition (covered)

7. Optional Laminate Tension Properties-Determine Critical Hole Condition (covered)

8. Optional Laminate Tension Properties - Determine Critical Environment (not covered) Critical Environment may be a Function of the Laminate Stiffness

9. FAA/NASA/IndustryMaterial Specification Guidelines Recommendation: Expand explanation to highlight that material specification acceptance values are not the same as B-basis design allowables (intended for different objectives). Acceptance values are different due to adjustments for acceptance sample size & alpha. As written, these two values are presented as being somewhat interchangeable. • Material specification acceptance values are intended for control of incoming material. • B-basis / A-basis design allowables are intended to provide a certain level of statistical confidence for design M.S. calculations.

10. FAA/NASA/IndustryMaterial Specification Guidelines Recommendations: • Consider including additional regulatory references (relevant FAR’s and AC’s) to tie in true source of material & process spec requirements. • Consider more discussion of relationship between material specification acceptance values and design values from the perspective of “Periodic Property Testing”. While updating specification values is a common practice, updating design values may require significant engineering expense to revisit M.S. calculations. This effort may only be justifiable to support growth in loads or to account for a statistically significant negative shift in material properties.

11. FAA/NASA/IndustryMaterial Specification Guidelines Recommendations on Level 1 Changes: • Some seemingly trivial changes, such as backing paper and release papers, can render the material unusable to the end user due to producibility issues (ATLM, Fiberplacement etc.). Such changes should require prior end user approval. • “Alternate vendor for chemically identical raw materials”. This statement should include “..chemically and physically identical..”. Physical aspects of constituent resin chemicals, such as particulate size and shape, can have a significant effect on the properties of the mixed resin even if the constituents are chemically identical.