Experimental and numerical investigations on structural behavior of S-UHPC-S composite walls under near-field blast load
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Three kinds of C/C composites with different matrix carbon were prepared, and then the ring-block sliding friction behavior was tested on M2000 tester against C/C ring with smooth lamination structure pyrocarbon matrix(SL).The results show that the coefficient of friction(COF) of the composite with SL(composite A) or resin carbon matrix(composite B) is lower than that of the composite with rough lamination structure pyrocarbon matrix(composite C). The COF of composite A and B decreases with the increase of load, while that of composite C increases at first and then decreases with the highest value of 0.145 at 100 N. The volume loss of composite A and B is close and remain stable when the load is higher than 80 N with the highest value is only 0.39 mm3. But the value loss of composite C increases up to the highest value of 1.47 mm3at 100 N and then remains some fluctuation. The COF of composite A can reach the stable value quickly while those of composite B and C still decrease after 5 hours' test. SEM images of worn surface show that some large film on composite A is peeled off, some dotted adhesive wear scar can be found on the worn surface of composite B. Abrasive worn is the main wear mechanism for tribological behavior of the three C/C composites.
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Matrix (chemical analysis)
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Temperature cycling
Acoustic Emission
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Spray pyrolysis
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For the demolishing construction of a 3-span continuous box girder bridge with span arrangement(18+26.4+18) m,a demolishing scheme was proposed and designed,i.e.,the main girder of the bridge was stabilized by the bailey truss and suspenders,the girder was cut into 3 sections by the diamond steel wire cutting method,the section of the girder over the central span was lifted away by the overhead launching gantry and shifted to an open ground where it was then broken into pieces.The side spans flanking the central span and the 2-m remaining sections of the central span were broken in situ on staging.To ensure the construction safety,the internal force and deformation of the structure in the construction process were analyzed by the finite element software.The results of the analysis indicated that the deflection of the bailey truss was greater than that of the main girder,which caused great tensile force in the suspenders at both sides of the truss and little tensile force in the suspenders in the middle.In that case,the suspenders were pre-tensioned before lifting and in the lifting process,the axial forces of the suspenders were adjusted.Presently,the demolishing of the bridge has been completed and the whole process of the demolishing is safe and controllable.
Box girder
Internal forces
Bridge (graph theory)
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Experiments were conducted to establish a correlation between the weight loss of a polyimide (PMR- 15) matrix and graphite fibers and the in-plane shear properties of their unidirectional composites subjected to different isothermal aging times up to 1000 hr at 316 C. The role of fiber surface treatment on the composite degradation during the thermo-oxidative aging was investigated by using A4 graphite fibers with three surface modifications: untreated (AU-4), surface treated (AS-4), and surface treated and sized with an epoxy-compatible sizing (AS-4G). The weight loss of the matrix fibers, and composites was determined during the aging. The effect of thermal aging was seen in all the fiber samples in terms of weight loss and reduction in fiber diameter. Calculated values of weight loss fluxes for different surfaces of rectangular unidirectional composite plates showed that the largest weight loss occurred at those cut surfaces where fibers were perpendicular to the surface. Consequently, the largest amount of damage was also noted on these cut surfaces. Optical observation of the neat matrix and composite plates subjected to different aging times revealed that the degradation (such as matrix microcracking and void growth) occurred in a thin surface layer near the specimen edges. The in-plane shear modulus of the composites was unaffected by the fiber surface treatment and the thermal aging. The shear strength of the composites with the untreated fibers was the lowest and it decreased with aging. A fracture surface examination of the composites with untreated fibers suggested that the weak interface allowed the oxidation reaction to proceed along the interface and thus expose the inner material to further oxidation. The results indicated that the fiber-matrix interface affected the composite degradation process during its thermal aging and that the the weak interface accelerated the composite degradation.
Thermal Stability
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Evidence for existence of composite copper/oxygen vacancy nanofilaments is presented. The composite conductive nanofilment (CF) is a serial resistive connection of Cu and Vo CFs forming a composite Vo/Cu CF where the Cu filament segment is formed first and Vo filament completes the composite CF. A composite CF has been also formed in reverse order as Cu/Vo. Both composite CFs, Vo/Cu and Cu/Vo, display Vform at considerable lower voltages than monolithic CFs.
Resistive touchscreen
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Experiments were conducted to study the effects of thermo-oxidative stability (weight loss) and fiber surface modification on the inplane shear properties of graphite/PMR-15 unidirectional composites. The isothermal aging was conducted at 316°C and up to 1000 hours of aging times. The role of fiber surface treatment on the composite degradation during the thermo-oxidative aging was investigated by using A-4 graphite fibers having three different surface modifications, namely untreated (AU-4), surface treated (AS-4), and surface treated and sized with epoxy-compatible sizing (AS-4G). Weight loss of matrix, fibers, and composites was determined during the aging. The effect of thermal aging was seen in all the fiber samples in terms of their weight loss and reduction in fiber diameter. Calculated values of weight loss fluxes for different surfaces of rectangular unidirectional composite plates showed that the largest weight loss occurs at those cut surfaces where fibers are perpendicular to the surface. Consequently, the largest amount of damage was also noted on these cut surfaces. Optical observation of neat matrix and composites plates subjected to the different aging times revealed that the degradation (such as matrix microcracking, void growth, etc.) occurred within a thin surface layer near specimen edges. The inplane shear modulus of the composites was unaffected by the fiber surface treatment and the thermal aging. The shear strength of the composites having the untreated fibers was the lowest and it decreased with aging. Fracture surface examination of the composites having untreated fibers suggests that the weak interface allows the oxidation reaction to proceed along the interface and thus expose the inner material to further oxidation. The results indicate that fiber-matrix interface affects the composite degradation process during its thermal aging and that the weak interface accelerates the composite degradation.
Thermal Stability
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For this study,the installation process of the steel box girder of the main bridge of Xiazhang Sea-Crossing Bridge was taken as the background.The lifting points for installation were optimized through the finite element calculation of the steel box girder sections.Originally,there was a small number of lifting points and the problem of stress concentration also existed,after the optimization,a sound installation condition of multiple lifting points and good stress distribution were created.The natural vibration property of the sections of the steel box girder was studied to guide the application of the equipments which showed vibration during the construction process.The maximum stress near the derrick crane under the transient working condition was analyzed and calculated,so as to control the most unfavorable working stress during the construction process and ensure the safety of the construction.
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Box girder
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Carbon fibers
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