Application of Chemical Characterization for Product Control and Improved Reliability

Abstract

Traditional testing of incoming materials relies extensively on physical/mechanical evaluations which require long flow time and are labor intensive.

Boeing Aerospace Quality Assurance has been developing and implementing Chemical Characterization techniques for the last nine years. The sophisticated analytical methods, which fingerprint materials using advanced instrumental techniques, provide rapid material identification and formulation verification.

The advanced instruments utilized and the types of materials characterized are discussed with emphasis on applications. The several benefits from implementing Chemical Characterization, including costs savings, are also presented.

The principal methods for qualifying materials during receiving inspection rely extensively on physical/mechanical evaluations, such as tensile testing. These traditional tests, which require long flow time for sample preparation, conditioning, machining, coupon preparation and data analysis are very labor intensive. In addition, inspection results provide only subjective pass/fail information which does not identify changes in material formulations that can detrimentally impact product quality and reliability.

Boeing Aerospace Quality Assurance is vitally concerned about changes in the formulation of materials. Several incidents in the past 10 years have emphasized this concern. Cured sealants and electrical potting compounds have reverted to their precured monomeric components while in service. Additionally, problems have been experienced with composite materials adhesion, cure and fire retardant properties. In some cases, conventional test methods passed marginal or unacceptable materials because they lacked the sensitivity to detect formulation changes; changes which were ultimately found to be responsible for hardware failure. Consequently corrective action often required extensive retrofit of in-service hardware at considerable expense.

The following illustration Figure 1 depicts the conventional physical teat method and associated problems. As can be seen in this figure, conventional testing requires excessive flow time for sample preparation and conditioning and lacks the capability to control material formulation which is essential for insuring uniform product quality.

The challenge at Boeing was to develop and implement more efficient test methods that would (1) quantitatively reflect material performance characteristics and (2) detect critical formulation changes prior to costly manufacturing processing or incorporation of a marginal material into production hardware, Figure 2.