Abstract:In this paper， an orthogonal trapezoidal honeycomb aluminum material is prepared， which is intended to be used as an energy-absorbing device for vehicles instead of traditional energy-absorbing box， and the impact mechanics and energy-absorbing properties of the material at low speed are studied. Firstly， a structure of orthogonal trapezoidal honeycomb aluminum was fabricated using an adhesive bonding method. Experimental methods were then employed to study the in-plane compression process of the material， obtaining stress and energy absorption characteristics of the material. Secondly， the deformation and stress of the material were analyzed by theoretical analysis method， and the energy absorption of the material was compared with the test results. Finally， the loading process of the material was simulated by means of simulation. Combined with the optimization design method， the optimal energy absorption parameters of the material were obtained as a plate thickness of 0.50 mm and an upper side length of 3.0 mm. At this time， the specific energy absorption of the orthogonal trapezoidal honeycomb aluminum material can reach 28.8 kJ/kg， which is better than the traditional energy absorption box structure. It characterizes the feasibility of orthogonal trapezoidal honeycomb aluminum replacing traditional energy absorption materials.

Abstract:To explore the axial compressive stress-strain relationship of Ultra-High Performance Seawater Sea-sand Concrete （UHPSSC） and study the influence of steel fiber volume content on the axial compressive mechanical properties and axial compressive complete stress-strain curve of UHPSSC， the complete stress-strain curve of UHPSSC was obtained through the compression tests with the Instron 1346 universal material ， and the Pycharm curve fitting program was used to fit and modify the existing concrete complete stress-strain curve model. The results show that the higher the steel fiber content， the smaller the damage degree of UHPSSC under axial compression， and the compressive strength and peak strain also increase. The rising section of the UHPSSC stress-strain curve fitted by the existing model is similar to the test curve， and the gap between the falling section and the later stage is large. By modifying the shape parameters of the descending section， a modified model more suitable for describing the complete stress-strain curve of UHPSSC was obtained， and the applicable scope of the modified model was verified.

Abstract:In order to solve the engineering problem of continuous box girder bridges with severe cracking due to excessive self-weight， a combined PC and steel-UHPC composite beam continuous hybrid girder bridge is proposed. To investigate the mechanical properties of the UHPC layer in the new type of bridge as well as its effect on the force transfer mechanism of the joint section of steel-UHPC composite girder， a Midas integral FE model was established to obtain the internal force of the structure under the design load effect， taking Binzhou Yellow River Bridge in Shandong Province as the engineering background. Meanwhile， two FE sub-models of the joint section of the steel-UHPC composite girder with and without UHPC layer were established by using ANSYS， respectively. The differences between the two models in the force performance and load transfer mechanism of the steel-concrete joint section were compared， and the mechanical properties of the UHPC layer were analyzed. The FE results show that： 1） Except for some stress concentration areas， the stresses in all parts of the new structure are lower than the strength design value， meeting the design requirements； 2） Under the most unfavorable bending moment， the maximum tensile stress of the top plate of the new structure’s steel box girder is significantly reduced， which can significantly improve the fatigue life of the steel structure； 3） The stress at the interface of the top plate of the new structural concrete beam is decreased by about 5%~29%， which can improve the cracking resistance； 4） The maximum tensile and compressive stresses of the UHPC layer are lower than their design strength， meeting the design requirements， and the UHPC layer can share 4%~10.9% of the bending moment of the joint section.

Abstract:To solve the problem of mismatch between design parameters and actual mechanical properties of pavement structure， typical cement stabilized macadam was selected to carry out uniaxial compression and direct tensile tests under different cement dosages and loading speeds. The stress-strain characteristics were studied， and the variation of compressive and tensile strength（Rc & Rt）/ modulus（Ec & Et）/ Poisson’s ratio（μc & μt） and their relationships were analyzed， revealing the different mechanical properties of cement stabilized macadam under tension and compression. The results show that the stress-strain properties of cement stabilized macadam under tension and compression are in accordance with the bilinear characteristics of bi-modulus theory. A cement dosage range of 2% to 3% is identified as the transition zone where the mechanical properties change. The tensile and compressive parameters exhibit a strong nonlinear relationship with the loading speeds and cement dosages. Among the influencing factors， the influence of cement dosage on tensile and compressive parameters is much greater than the loading speed. In terms of mechanical parameters， the modulus is most affected by cement dosage and loading speed， followed by strength， and Poisson’s ratio. Compared with compressive parameters， tensile parameters are more significantly affected by these two factors. The Ec/Et and the μc/μt are less affected by loading speed and cement dosage. The Rc/Rt decreases gradually with the increase of cement dosage. When the cement dosage exceeds 3%， the Rc/Rt tends to be stable. Based on these findings， a quantitative value model for the tensile and compressive mechanical parameters of cement stabilized macadam is established. The research results can provide a basis for the parameter value of pavement structure design based on bi-modulus theory.

Abstract:The effect of the concentration of silane coupling agent KH560 on the dispersion and placement stability of the vitrified bond was investigated， together with the mechanism of modification. Furthermore， cBN grinding tools were prepared with vitrified bond of different dispersion， and the influence of modification methods of vitrified bond and storage time on the micro-mechanism， mechanical properties and grinding performance of cBN grinding tools were studied. The results show that when the KH560 addition was 3.0%， the vitrified bond powder displayed the best dispersion and placement stabilization. The microstructure of CBN abrasive tools prepared by using 3.0%KH560 modified vitrified bond powder for 360 h was uniform， and the bending strength and Rockwell hardness reached the maximum values of 189.3 MPa and 100.15 HRB， which were 12.72% and 5.82% higher than those of unmodified cBN grinding tools respectively. The surface roughness value of the workpiece was 0.054 μm when using this grinding tool to honed the inner holed of bearing steel， which was 48.6% lower than that of the workpiece processed by unmodified cBN grinding tools.

Abstract:SiCp/6013Al composites with a uniform structure and good particle dispersion were prepared by ball milling， cold isostatic pressing， hot isostatic pressing and hot extrusion process. Using transmission electron microscopy， scanning electron microscopy， and room temperature mechanical performance testing， the precipitation behavior and mechanical properties of 15% SiCp/6013Al composites under different artificial aging temperatures after solution treatment were studied. The results show that the precipitation behavior of the composites is controlled by thermal diffusion， and the precipitation accelerates when the temperature increases. The main strengthening phase of the composites is Mg2Si， while SiC particles can significantly enhance the strength of the composites， but also lead to a rapid decline in the plasticity of the composites. Compared with 6013 aluminum alloy matrix， 15% SiCp/6013Al composites can reach peak aging at a lower temperature and in a shorter time. After artificial aging treatment， the maximum hardness is 180 HV0.2 and the tensile strength is 522 MPa.

Abstract:Adopting the improved ASTM D1037 aging method， a series of artificial aging tests with 0， 3， and 6 times of dry-wet cycling were designed for larch laminate specimens to study the effect of long-term temperature and humidity alternation on the mechanical properties of the glulam. The influences of different times of dry-wet cycling on the macroscopic characterization of glulam， micromorphology， material density， and strength indexes of the compressive strength parallel to the grain， tensile strength parallel to the grain， bending strength， and shear strength of the rubber layer was analyzed. Results show that strength indexes decreased obviously after dry-wet cycling. With the increase in the number of dry-wet alternations， the decrease of the strength indexes of the specimen increases. After 6 times of dry-wet cycling， the decline amplitude of the compressive strength parallel to the grain， tensile strength parallel to the grain， bending strength， and shear strength of the rubber layer increased in turn， within 26.75%， 29.64%， 33.57%， and 40%， respectively. Compared with the initial crack， the effect of alternating dry and wet on the bending strength is more significant. The relationship between dry-wet alternation times and the strength can be fitted by a power function. Based on the corresponding relationship between the times of dry and wet alternations and time， time-varying models of larch glulams compressive， tensile， bending， and shear strength of the rubber layer were established.

Abstract:Clarifying the differences of mechanical properties in different anatomical regions of bone can providean important basis for constructing the finite element model of the bone with high biofidelity. One sample was pre?pared from each of the anterior，posterior，medial，and lateral anatomical regions of the bovine femoral shaft. Eachsample was tested at 18 points utilizing a Berkovich nanoindenter tip，and the time history of the loading force and in?dentation depth was recorded to obtain the indentation modulus and hardness. The indentation modulus of the ante?rior，posterior，medial and lateral regions of the long bone were 20.78 ± 2.66 GPa，18.66 ± 2.57 GPa，16.39 ± 2.29GPa，21.57 ± 2.19 GPa respectively，and hardness were 0.65 ± 0.79 GPa，0.58 ± 0.08 GPa，0.44 ± 0.06 GPa，0.61± 0.15 GPa respectively. Variance analysis showed that anatomical region had a significant effect on indentation modulus and hardness（p < 0.001）. Multiple comparisons between groups showed that the indentation modulus andhardness of the anterior specimen were significantly higher than those of the lateral specimen，the indentation modu?lus and hardness of the medial specimen were significantly higher than those of the lateral specimen，the hardness ofthe posterior specimen was significantly higher than that of the lateral specimen，and the indentation modulus of themedial specimen was significantly higher than that of the lateral specimen. Therefore，the use of heterogeneous mate?rials can help to improve the biological fidelity of the finite element model of the long bone.

Abstract:To obtain high volume fraction low angle grain boundary（LAGBs） and low volume fraction recrystallization microstructure so as to improve the comprehensive properties of aluminum alloy, the effects of High Strain Rate Rolling (HSRR) processing parameters on microstructures and mechanical properties of 7050 aluminum alloy were explored. Electron backscatter diffraction（EBSD），Transmission Electron Microscopy（TEM） were used to characterize the volume fraction of low angle-grain boundarys（LAGBs） and dynamic precipitates. The results show that a high fraction of LAGBs can be obtained by HSRR, and the fraction of LAGBs increases with the increasing strain rate but decreases with the temperature. The fraction of LAGBs is 95.6% with the rolling parameter of 370 ℃/20 s-1. The alloy rolled at 400 ℃/20 s-1 exhibits good comprehensive mechanical properties after 470 ℃/0.5 h short-term solution treatment and 120 ℃/24 h aging treatment, with the ultimate tensile strength of 530 MPa，the yield strength of 442 MPa，the elongation at fracture of 19.1%. The mechanical properties of the plates rolled with the strain rate of 20 s-1 are better than that with the strain rate of 10 s-1 at the same rolling temperature.

Abstract:In order to explore the engineering mechanical properties of the aeolian sand subgrade treated by pyrolysis residue of oil sludge, the compaction characteristics, resilience modulus, California bearing ratio (CBR), and direct shear characteristics of the aeolian sand subgrade with different content of oil sludge pyrolysis residue, as well as the unconfined compressive strength with 25% content of residue were studied through laboratory tests. The results show that the maximum dry density is 2.071 g/cm3 when the content of oil sludge pyrolysis residue is 25%; the maximum rebound modulus is 160.61 MPa when the content is 15%; the CBR increases continuously with the increase ofresidue content, the CBR value of the sample decreases obviously after soaking in water, within the decrease ranging from 10.97% to 38.46%; the maximum internal friction angle is 34.35° when the content is 20%; the unconfined compressive strength values of the sample with 25% residue content exceed 0.4 MPa at 14 d and after 14 d. The comprehensive test results show that the pyrolysis residue of oil sludge can effectively improve the mechanical properties of the aeolian sand subgrade, and the residue can be used as filling material for the aeolian sand subgrade.