Investigation of intelligent features for CFRP structure in automotive safety systems
New stringent European Union regulations, on both emission and fuel consumption are driving the automobile manufacturers in continuous search of suitable lightweight materials. Carbon Fiber Reinforced Plastic (CFRP) is one of the most prominent lightweight materials in use. In addition to the benefit of reduction in weight, the inherent properties of CFRP materials such as acoustic emission, electrical properties of fibers etc. change with the applied load during elastic deformation and failure. This change in properties is the base of the presented idea to assign intelligence to current automotive safety structures made from CFRP material. This paper gives a short review of the work done by various researchers in the field of health monitoring of CFRP structures using electrical resistance. Further, experiments were performed for initial investigations to show the promising usage of the above explained intelligence features. Tube-like and plate-like specimens were used, because of their similarity with automotive structures. It can be concluded, that the mechanisms like elastic bending and micro buckling have very negligible influence on resistance change compared to other mechanisms. The results from the experiments show significant resistance change within 5 to 50 milliseconds after impact. This demonstrates the potential of this concept to be used for crash severity detection in automobiles.
Characterization of piezoresistance behavior in a CFRP unidirectional laminate
This paper aims at characterizing the piezoresistance behavior in a carbon fiber reinforced plastics (CFRP) unidirectional laminate under mechanical loading. A two-dimensional model is proposed using a DC circuit equivalent to an electric resistance network in the laminate to predict the resistance change due to tensile loading. The surface resistivity and the initial gage factor are expressed as a function of the off-axis angle in the model. The piezoresistance behavior in the fiber and transverse directions is predicted based on the resistance model associated with the probabilistic failure of conduction paths parallel and perpendicular to the fiber direction. The measured resistance in these directions increases linearly within the small tensile strain, while it increases nonlinearly at large strains. The measured resistance in the off-axis directions exhibits remarkable nonlinearity except the first linear region. The predicted initial gage factor becomes the maximum at an off-axis angle of 12° and is in reasonably good agreement with the experimental results.
Role of the coronoid process in varus osteoarticular stability of the elbow.
The role of the coronoid process in varus osteoarticular stability of the elbow was investigated in 10 cadaveric elbows. Testing was performed at multiple flexion angles after incremental removal of the coronoid. At each flexion angle, removal of more than 50% of the coronoid produced a statistically significant decrease in the load resisting varus displacement compared with all lesser resection levels (P < .003). There was a trend for decreasing load after removal of 50% of the coronoid. The mean decrease in load across all flexion angles was 10.1%, 50.4%, and 75.4% after removal of 50%, 75%, and 100% of the coronoid, respectively. Resistance to varus displacement tended to decrease more as a percent of control at lower flexion angles than at higher flexion angles after removal of more than 50% of the coronoid. The coronoid process was found to be a key varus stabilizer in the elbow and may contribute more to elbow stability in extension than in flexion.