Certification of damage tolerant composite structure

A reliability based certification testing methodology for impact damage tolerant composite structure was developed. Cocured, adhesively bonded, and impact damaged composite static strength and fatigue life data were statistically analyzed to determine the influence of test parameters on the data scatter. The impact damage resistance and damage tolerance of various structural configurations were characterized through the analysis of an industry wide database of impact test results. Realistic impact damage certification requirements were proposed based on actual fleet aircraft data. The capabilities of available impact damage analysis methods were determined through correlation with experimental data. Probabilistic methods were developed to estimate the reliability of impact damaged composite structures

An Efficient Method of Modeling Material Properties Using a Thermal Diffusion Analogy: An Example Based on Craniofacial Bone

The ability to incorporate detailed geometry into finite element models has allowed researchers to investigate the influence of morphology on performance aspects of skeletal components. This advance has also allowed researchers to explore the effect of different material models, ranging from simple (e.g., isotropic) to complex (e.g., orthotropic), on the response of bone. However, bone's complicated geometry makes it difficult to incorporate complex material models into finite element models of bone. This difficulty is due to variation in the spatial orientation of material properties throughout bone. Our analysis addresses this problem by taking full advantage of a finite element program's ability to solve thermal-structural problems. Using a linear relationship between temperature and modulus, we seeded specific nodes of the finite element model with temperatures. We then used thermal diffusion to propagate the modulus throughout the finite element model. Finally, we solved for the mechanical response of the finite element model to the applied loads and constraints. We found that using the thermal diffusion analogy to control the modulus of bone throughout its structure provides a simple and effective method of spatially varying modulus. Results compare favorably against both experimental data and results from an FE model that incorporated a complex (orthotropic) material model. This method presented will allow researchers the ability to easily incorporate more material property data into their finite element models in an effort to improve the model's accuracy

Attracting Cracks for Arrestment in Bone-Like Composites

Osteonal bones are crack-tolerant due to their repair activity and special tissue structures formed by interstitial material and osteons. Crack-resistant engineering structures may be developed by mimicking bones. In this paper, bone-like composite materials were modeled by using circular inclusions as osteons and their cement lines. A two-inclusion model was investigated to see how crack location and inclusion size and property variations affect the propagation of an initial crack between the inclusions. A four-inclusion model was studied to determine conditions for attracting cracks to inclusions for arrestment. The four-inclusion model was optimized in order to arrest any crack initiated within the interstitial material between the inclusions. The optimized model was verified with the FRANC2D software. The results showed that inclusions with effective elastic moduli smaller than that of the interstitial material always tend to attract cracks. On the contrary, an inclusion with effective modulus greater than that of the interstitial material has a tendency to repel cracks. A crack’s propagation direction can be changed by varying inclusions’ sizes and elastic properties. At optimal point, any crack initiated within the interstitial material between the four inclusions can be attracted to two inclusions for arrestment