Delaminations in composite laminates may de-velop from small cracks due to fabrication and impact load-ing,or from places of high stress concentration.The locationsof the delaminations are not determinate.In this rese...Delaminations in composite laminates may de-velop from small cracks due to fabrication and impact load-ing,or from places of high stress concentration.The locationsof the delaminations are not determinate.In this research,ananalytical solution for the free vibration of a composite beamwith two overlapping delaminations is presented.The dela-minated beam is analyzed as seven interconnected beamsusing the delaminations as their boundaries.The continuityand equilibrium conditions are satisfied between the adjoin-ing regions of the beams.Classical beam theory is applied toeach of the beams.Complex vibration behaviors emerge fordifferent sizes and locations of the delaminations.Compar-ison with analytical results reported in the literature verifiesthe validity of the present solution.展开更多
Air-coupled ultrasonic transducers are used to generate and receive Lamb waves in quasi-isotropic laminated composite beams for delamination detection. The influence of incident angle on the excited mode is studied. N...Air-coupled ultrasonic transducers are used to generate and receive Lamb waves in quasi-isotropic laminated composite beams for delamination detection. The influence of incident angle on the excited mode is studied. Numerical calculation and experimental results show that a pure Lamb wave mode can be generated if the transmitting transducer is oriented at a specific angle, and the receiving transducer can either be oriented to detect the same mode as that generated by the transmitter or to detect another mode generated by mode conversion at a defect. A three-dimensional finite element model is created to predict the interaction of Lamb waves with delamination, and some unique mechanisms of interaction between A0 mode Lamb waves and delamination are revealed in detail. The experimental results obtained on laminated composite beam using air-coupled ultrasonic transducers are well in accordance with finite element simulation results. Research results show that air-coupled ultrasonic guided waves can be used for delamination damage detection effectively in laminated composite beams.展开更多
为便于在钢-混凝土组合梁设计过程中,考虑主梁变截面、横梁刚度及各种复杂约束条件,简单准确地评估施工阶段钢梁的整体稳定性,在《公路钢结构桥梁设计规范》(JTG D64—2015)的框架下,参考BS EN 1993-1-1:2005和BS EN 1993-2:2006的相关...为便于在钢-混凝土组合梁设计过程中,考虑主梁变截面、横梁刚度及各种复杂约束条件,简单准确地评估施工阶段钢梁的整体稳定性,在《公路钢结构桥梁设计规范》(JTG D64—2015)的框架下,参考BS EN 1993-1-1:2005和BS EN 1993-2:2006的相关规定,总结出了一套实用性强的钢梁整体稳定性验算方法。以跨径布置分别为4×30 m,4×35 m,4×40 m主梁形式的连续钢板组合梁为例,运用上述稳定性验算方法,研究了横梁间距、抗弯刚度对主梁施工阶段整体稳定性的影响。理论分析和数值计算结果表明:钢梁整体稳定性不仅与弹性屈曲系数相关,也与施工期间的钢梁应力值相关;对于大跨径桥梁,由于恒载占比相对小跨径桥梁更大,导致施工阶段稳定性验算工况应力水平较高,更容易发生施工阶段钢梁失稳,应特别关注加强验算和构造处理;为便于设计人员简化设计流程,提出了一个d类截面Q345材质钢梁整体稳定的充分不必要条件:线弹性屈曲系数>4且钢梁最不利应力值<117.9 MPa;主梁整体稳定性随横梁刚度增大而增大,随横梁间距减少而增大,但通过提高横梁刚度来提高主梁整体稳定性的效率不如减少横梁间距;大于受压翼缘宽度30倍的横梁间距不能保证施工阶段的钢梁整体稳定性,横梁间距宜根据稳定性计算确定。展开更多
文摘Delaminations in composite laminates may de-velop from small cracks due to fabrication and impact load-ing,or from places of high stress concentration.The locationsof the delaminations are not determinate.In this research,ananalytical solution for the free vibration of a composite beamwith two overlapping delaminations is presented.The dela-minated beam is analyzed as seven interconnected beamsusing the delaminations as their boundaries.The continuityand equilibrium conditions are satisfied between the adjoin-ing regions of the beams.Classical beam theory is applied toeach of the beams.Complex vibration behaviors emerge fordifferent sizes and locations of the delaminations.Compar-ison with analytical results reported in the literature verifiesthe validity of the present solution.
基金supported by the National Natural Science Foundation of China(Grant Nos. 11272021 and 50975006)Beijing Natural Science Foundation(Grant No. 1122007)+1 种基金the Importation and Development of High-Caliber Talents Project of Beijing Municipal Institutions(No.CIT&TCD201304048)Beijing Nova Program(Grant No. 2008A015)
文摘Air-coupled ultrasonic transducers are used to generate and receive Lamb waves in quasi-isotropic laminated composite beams for delamination detection. The influence of incident angle on the excited mode is studied. Numerical calculation and experimental results show that a pure Lamb wave mode can be generated if the transmitting transducer is oriented at a specific angle, and the receiving transducer can either be oriented to detect the same mode as that generated by the transmitter or to detect another mode generated by mode conversion at a defect. A three-dimensional finite element model is created to predict the interaction of Lamb waves with delamination, and some unique mechanisms of interaction between A0 mode Lamb waves and delamination are revealed in detail. The experimental results obtained on laminated composite beam using air-coupled ultrasonic transducers are well in accordance with finite element simulation results. Research results show that air-coupled ultrasonic guided waves can be used for delamination damage detection effectively in laminated composite beams.
文摘为便于在钢-混凝土组合梁设计过程中,考虑主梁变截面、横梁刚度及各种复杂约束条件,简单准确地评估施工阶段钢梁的整体稳定性,在《公路钢结构桥梁设计规范》(JTG D64—2015)的框架下,参考BS EN 1993-1-1:2005和BS EN 1993-2:2006的相关规定,总结出了一套实用性强的钢梁整体稳定性验算方法。以跨径布置分别为4×30 m,4×35 m,4×40 m主梁形式的连续钢板组合梁为例,运用上述稳定性验算方法,研究了横梁间距、抗弯刚度对主梁施工阶段整体稳定性的影响。理论分析和数值计算结果表明:钢梁整体稳定性不仅与弹性屈曲系数相关,也与施工期间的钢梁应力值相关;对于大跨径桥梁,由于恒载占比相对小跨径桥梁更大,导致施工阶段稳定性验算工况应力水平较高,更容易发生施工阶段钢梁失稳,应特别关注加强验算和构造处理;为便于设计人员简化设计流程,提出了一个d类截面Q345材质钢梁整体稳定的充分不必要条件:线弹性屈曲系数>4且钢梁最不利应力值<117.9 MPa;主梁整体稳定性随横梁刚度增大而增大,随横梁间距减少而增大,但通过提高横梁刚度来提高主梁整体稳定性的效率不如减少横梁间距;大于受压翼缘宽度30倍的横梁间距不能保证施工阶段的钢梁整体稳定性,横梁间距宜根据稳定性计算确定。
