高弯曲性薄型层压基材——NFX系列

概述了高弯曲性层压型基材——NFX系列的开发,它的特征在于高弯曲性和低刚性,它是FPC用薄型高弯曲性2层FCCL。

Bending properties and fracture mechanism of C/C composites with high density preform

C/C composites with banded structure pyrocarbon were fabricated by fast chemical vapor infiltration（CVI）,with C3H6 as carbon source,N2 as carrier gas,and three-dimensional（3D） 12K PAN-based carbon fabric with high density of 0.94 g/cm3 as preform.Experimental results indicated that the fracture characteristics of C/C composites were closely related to the frequency of high-temperature treatment（HTT） at the break of CVI process.According to the load？displacement curves,C/C composites showed a pseudoplastic fracture after twice of HTT.After three times of HTT,load？displacement curves tended to be stable with a decreasing bending strength at 177.5 MPa.Delamination failure and intrastratal fiber fracture were observed at the cross-section of C/C composites by scanning electronic microscope.Because the content of pyrocarbon and fibers has a different distribution in layers,the C/C composites show different fracture characteristics at various regions,which leads to good toughness and bending strength.

Effect of fiber type on the bending and uniaxial tensile properties of high-strength high-ductility cementitious composites

To investigate the effect of fiber types on bending and tensile properties of high-strength,high-ductility cementitious composites( HS-HDCCs), ultra-high-molecular-weight polyethylene( PE) fibers,polyvinyl alcohol( PVA) fibers,and copper-plated micro steel fibers were selected as the reinforcement materials. The bending and tensile properties of HS-HDCCs with different fibers with a volume fraction of 2% were studied. The results indicate that PE,PVA,micro steel,and PVA-PE hybrid fibers impart varying degrees of toughening and improve the tensile strength. During the tensile and bending processes,HS-HDCCs with micro steel fibers exhibit a strain-softening phenomenon. HS-HDCCs with PVA fibers or with PVA-PE hybrid fibers can achieve multiple cracking behaviors and strain hardening phenomenon to a certain extent and show slight high-ductility characteristics. HS-HDCCs with PE fibers exhibit multiple cracking behavior and strain hardening phenomenon and show significant high-ductility characteristics. The test results can provide a basis for selecting fibers suitable for HS-HDCCs reinforcement.

Mechanism of improving ductility of high strength concrete T-section beam confined by CFRP sheet subjected to flexural loading

For the purpose of inventing a new seismic retrofitting method for the reinforced high strength concrete （HSC） T-section beam using carbon fiber reinforced polymer （CFRP） sheet, three series, a total of twelve T-section beams with nine specimens confined by CFRP sheet in the plastic zone and three control beams were conducted up to failure under four-point bending test. The effectiveness of confining CFRP sheet on improving the flexural ductility of tmstrengthened T-section beams was studied. The parameters such as the width and the thickness of CFRP sheet and the type of T-section were analyzed. The experimental results show that ductility and rotation capacity of plastic hinge can be improved by the confinement of CFRP sheet, and the ductility indices increase with the increment of width and thickness of CFRP sheet. A plastic rotation model considering the width of CFRP sheet and the effect of flange of T-section beam is proposed on the basis of the model of BAKER, and the test results show a good agreement with the perdicted results. The relevant construction suggestions for seismic retrofitting design of beam-slabs system in cast-in-place framework structure are presented.

Bending Modulus Measurement of Single High Performance Fiber

The bending modulus property of high performance fiber is an important property for both polymer science and engineering. The measurement of the bending performance is, however, difficult because of the thin size of the fiber. We have measured this property by the axial compression bending method where single fiber with suitable slenderness is compressed in the fiber axial direction to obtain the peak point of the force-displacement curve. Then the bending modulus and the flexural rigidity can be calculated by measuring the protruding length and diameter of fiber needles and the critical force, Pcr. The measured data show that the bending characteristics of all kinds of high performance fiber are dissimilar evidently.

Flexural response of reinforced concrete beams strengthened with post-poured ultra high toughness cementitious composites layer

Four-point bending tests were conducted up to failure on eleven reinforced concrete (RC) beams and strengthening beams to study the effectiveness of externally pouring ultra high toughness cementitious composites (UHTCC) on improving the flexural behavior of existing RC beams.The strengthening materials included UHTCC and high strength grade concrete.The parameters,such as thickness and length of strengthening layer and reinforcement in post-poured layer,were analyzed.The flexural behavior,failure mode and crack propagation of composite beams were investigated.The test results show that the strengthening layer improves the cracking and ultimate load by increasing the cross section area.Introducing UHTCC material into strengthening not only improves the bearing capacity of the original specimens,but also disperses larger cracks in upper concrete into multiple tightly-spaced fine cracks,thus prolonging the appearance of harm surface cracks and increasing the durability of existing structures.Compared with post-poured concrete,UHTCC is more suitable for working together with reinforcement.The load?deflection plots obtained from three-dimensional finite-element model (FEM) analyses are compared with those obtained from the experimental results,and show close correlation.

Research on spring-back behavior of high strength steel sheets

To investigate the spring-back behavior of dual-phase （DP） steel, V-shape spring-back experiments with different bending angles, relative bending radii and blank holding forces were carried out in this paper. It is concluded that with the increase of V-shape angle or blank holding force, the spring-back of DP steel sheets decreases; while raising fiIlet radius of punch, which has the most apparent effects on spring-back, advances spring-back angle. Among DP590, DP780 and DP980, higher strength yields more notable spring-back due to larger elastic deformation. The difference of spring-back among these materials is relevant with the microstructure and mechanical properties. The total elastic deformation approximately equals the ratio of the strength corresponding to the applied load to the modulus of elasticity.