18 TH INTERNATIONAL CONFERENCE ON COMPOSITE MATERIALS 1 Introduction Criteria of strength, stiffness, fatigue and damage tolerance criteria are necessary to the composites design of the airplanes. For the strength criteria, the first ply failure (FPF) is extensively used. In Hinton, Kaddour and Soden [1] are showed failure criteria comparing with the experimental results. The results showed the difficulty to have an unique criteria that agree with all experimental results. A new criteria is being proposed in Stephen W. Tsai [2] based in the micro-mechanics theory. In this new approach the information about failure in the fiber, resin and interfaces can be obtained. Temperature, humidity, load frequency and stress ratio considered in this criteria are useful for composites design and analysis. Therefore the main purpose of this paper is to describe two applications that were made in the EMBRAER airplanes development program, considering this theory. It should be pointed out that the results of this tool were used to give directives to the certification campaign. The test results, confirmed the expectations. 2 Certification Challenge Definitions 2.1 Environmental Load Factor (ELF) There are many challenges and issues in the aeronautics certification. When the subject is composites structure, the ELF is one that is uncertain to obtain. ELF is a factor that employer prefers to use in the room temperature test condition (figure 1) instead to test the component inside an ambient with temperature and humidity controlled, figure 2. In this case, the test load is increased by ELF. ELF = 1.00 means that the component is being tested exactly in the real critical condition. Another factor that influences the weight of the component is the Load Enhancement Factor (LEF) as described in the MIL-HDBK-17 [3] and [4]. In the Phenom 100, EMBRAER airplane, the empennage test was overloaded with ELF and LEF. 2.2 Spectrum Loading Reduction One issue that affects the cost of the certification is the test time duration. In the certification is necessary to show residual strength in the ultimate load after fatigue cycles of the airplane [5], [6]. Therefore the challenge in this case is to decide about the truncation [3, 10] and/or reduction of the spectrum loading in the fatigue test without affect the original condition. The figure 3, shows one interpretation of the truncation proposed in the cited references. This decision affects the test duration and consequently the cost of the certification. One suggestion about spectrum truncation is the rule stated in the MIL-HDBK-17 and that is reproduced here: “Although there are no general guidelines for spectrum truncation for composite fatigue tests, the fatigue threshold of the material is usually used to determine the cycles to be truncated. Stress (strain) levels below the fatigue threshold are considered to cause no fatigue damage (initiation or progression) and theoretically can be removed from the spectrum without changing the test results. However, in practice, the truncation level is usually a certain percentage of the A- or B-basis fatigue threshold (e.g. 60% to 70%)”. In the Phenom 300, EMBRAER airplane, the composites flap test was the critical way to the certification. That is, the test duration considering the original spectrum loading would affect the deadline of the certification campaign. So, the reduction and/or truncation in the original fatigue spectrum would be necessary to do. Then, using the tool [8], a simulation was performed to decide about the proposal test which goal was MICRO-MECHANICS THEORY APPLIED IN AERONAUTICAL PRODUCT DEVELOPMENT. F.K. Arakaki 1 * 1 Technological Development , EMBRAER S.A., São José dos Campos, Brazil * Corresponding author (francisco.arakaki@embraer.com.br ) Keywords: micro-mechanics theory, certification, airplane applications