There are numerous aspects and questions related to the use of composite materials for primary structures in aircraft where the structural integrity is the most important factor. This is especially true if the main co...There are numerous aspects and questions related to the use of composite materials for primary structures in aircraft where the structural integrity is the most important factor. This is especially true if the main concerns are that the material should have good reliability and durability for the primary structural application. Composite laminates are highly sensitive to out-of-plane failure due to their low inter laminar fracture toughness. An alternate method to increase the damage resistance is through three-dimensional fibrous reinforcement such as through-the-thickness stitching with a single fiber as the thread. Recent studies have shown that the stitching of standard laminates can enhance damage tolerance to levels obtainable with toughened resin systems. However, for next-generation aircraft, material improvement alone is not enough to assure or increase the safety and reliability of the structure. Continuous damage monitoring during operation will become an important issue in aircraft safety. Embed ding fiber Bragg grating (FBG) technology into the composite structure as strain sensors could potentially solve the above problem because the FBG can be used to detect and characterize the damage before it reaches a critical stage. The model used to represent this problem is a 6 × 6 Vectran stitched carbon/ epoxy laminate under tension loading, and the real-time monitoring using the FBG strain sensors is combined with acoustic emissions that were conducted during the test. A numerical laminate theory using a rebar element and first-ply failure criterion is performed to determine the preferred area on the specimen for the placement of the FBG before manufacturing and testing. Experiments are presented to determine the damage growth that was quantified with an ultrasonic (water immersion) c-scan. In this research, the FBG successfully detected and characterized the damage in the carbon/epoxy stitch laminate caused in tension loading cases. The FBG is enhanced with acoustic emission data and can quantitatively 展开更多
Cuprammonium fabrics are susceptible to punctuation of the sewing needle during the manufacturing processes of a garment.This type of punctuation splits the yarns in the fabrics,creates ladder-like sewing defects,and ...Cuprammonium fabrics are susceptible to punctuation of the sewing needle during the manufacturing processes of a garment.This type of punctuation splits the yarns in the fabrics,creates ladder-like sewing defects,and seriously affects the aesthetics of the finished garment.To minimize this seam damage,a sandwiched structure of cuprammonium fabrics with a fusible interlining was proposed to enhance the friction between the yarns in the fabrics.A measurement system was set up to evaluate the seam damage,and the effects of stitch length and seam width on the seam damage were studied.The seam damage tended to become less severe as the stitch length increased.The addition of the fusible interlining between two pieces of the fabrics could effectively suppress the seam damage.The seam margin should be below or equal to 5 mm for the stitch length of 2.0 mm.An excessive seam margin might lead to a distorted seam.展开更多
文摘There are numerous aspects and questions related to the use of composite materials for primary structures in aircraft where the structural integrity is the most important factor. This is especially true if the main concerns are that the material should have good reliability and durability for the primary structural application. Composite laminates are highly sensitive to out-of-plane failure due to their low inter laminar fracture toughness. An alternate method to increase the damage resistance is through three-dimensional fibrous reinforcement such as through-the-thickness stitching with a single fiber as the thread. Recent studies have shown that the stitching of standard laminates can enhance damage tolerance to levels obtainable with toughened resin systems. However, for next-generation aircraft, material improvement alone is not enough to assure or increase the safety and reliability of the structure. Continuous damage monitoring during operation will become an important issue in aircraft safety. Embed ding fiber Bragg grating (FBG) technology into the composite structure as strain sensors could potentially solve the above problem because the FBG can be used to detect and characterize the damage before it reaches a critical stage. The model used to represent this problem is a 6 × 6 Vectran stitched carbon/ epoxy laminate under tension loading, and the real-time monitoring using the FBG strain sensors is combined with acoustic emissions that were conducted during the test. A numerical laminate theory using a rebar element and first-ply failure criterion is performed to determine the preferred area on the specimen for the placement of the FBG before manufacturing and testing. Experiments are presented to determine the damage growth that was quantified with an ultrasonic (water immersion) c-scan. In this research, the FBG successfully detected and characterized the damage in the carbon/epoxy stitch laminate caused in tension loading cases. The FBG is enhanced with acoustic emission data and can quantitatively
基金Education and Scientific Research Foundation for Middle-Aged and Young Teachers of Fujian Province,China(No.JAT170498)。
文摘Cuprammonium fabrics are susceptible to punctuation of the sewing needle during the manufacturing processes of a garment.This type of punctuation splits the yarns in the fabrics,creates ladder-like sewing defects,and seriously affects the aesthetics of the finished garment.To minimize this seam damage,a sandwiched structure of cuprammonium fabrics with a fusible interlining was proposed to enhance the friction between the yarns in the fabrics.A measurement system was set up to evaluate the seam damage,and the effects of stitch length and seam width on the seam damage were studied.The seam damage tended to become less severe as the stitch length increased.The addition of the fusible interlining between two pieces of the fabrics could effectively suppress the seam damage.The seam margin should be below or equal to 5 mm for the stitch length of 2.0 mm.An excessive seam margin might lead to a distorted seam.
