Influence of static pre-loading on the dynamic bending strength of concrete with particle element modeling

Experimental tests show that static pre-loading has a significant effect on the dynamic strength of concrete.Based on meso-scale particle element model,numerical simulations of dynamic bending tests with pre-loading are performed.Complete stress–strain relationships are then obtained.Significant increase in dynamic strength is found when the pre-loadings are imposed within the elastic limit of concrete.However,when the imposition of pre-loadings reaches the plastic or softening range,dynamic strengths may gradually decrease along with the increase in pre-loadings.The distribution of energy components and the failure modes are discussed to explain the mechanisms of the phenomena.

Effect of heating-rate on failure temperature of pre-loaded magnesium alloy

The response and failure of magnesium alloy AZ31 specimens subjected to different pre-loaded-stress levels and heating rates were investigated with a Gleeble-1500 thermo-mechanical material testing system.It is found that the increases of either pre-loaded stresses or heating-rates decrease the failure temperatures of the specimens.The metallographs of the tested specimens were also observed.It is shown that the high heating-rate may cause stronger local thermal inconsistency,which remarkably increases the microdefects and reduces the macroscopic mechanical properties of the material.

Finite Element Analysis on the Pre-load Structures of the Central Solenoid for the HT-7U Device

The central solenoid is an important part of the HT-7U device. In this paper， the computational analysis of the stress and the displacement on the pre-load structures of the central solenoid have been made by the finite element analysis system COSMOS/M2.0 under room and/or operating temperature. According to the analytical results, the clip aprons and compression plates are all satisfied with safety design criteria.

Linear monitoring for cast-in-place reinforced concrete arch bridge construction

Linear monitoring is an important link of bridge construction control,which is conducted in key processes of construction to ensure the security of bridge in construction procedure. Combining with main arch construction monitoring program of No. 2 bridge in north district of Changbai international tourism resort,main content and key technologies are recommended. Considering the various influential factors during the construction process,linear adjustment is handled to ensure that the stress and linear of main arch meet design requirements.

Thermal Stress and Assembling Parameters Evolution of CMC Bolted Joint under Transient Thermal Loads

Ceramic matrix composite(CMC) and superalloy bolted joints have exhibited great potential for high temperature hot structure application in hypersonic aircraft. In service conditions, the thermal expansion mismatch between CMC and superalloy plates will cause complex thermal stress and strain distributions at hole-edge areas and assembly parameters changes of the joints under elevated temperatures. These effects might lead to early damage of joint structure, which will endanger the structural integrity and load carrying capacity of aircraft components. In the present study, transient heat transfer and thermo-structural analysis of C/SiC composite and superalloy bolted joint were carried out by using a commercial FEA software ABAQUS. The stress distributions at hole-edge areas, pre-load loosening, and variation of bolt-hole clearance of CMC bolted joints under transient temperature rises were discussed for better understanding of high temperature structural behaviors. Results showed that pre-load declined with the increase of imposed hot side temperature, due to the thermal expansion mismatch between CMC and superalloy. The bolt-hole clearance for the composite plate decreased, whereas the clearance for the superalloy plate increased with the rise of temperature.

Influence of pre-load coefficient of TPJBs with even number pads on shaft lateral vibration

For a rotating machine with one or more tilting pad journal bearings (TPJBs), it is acommon state that pad-to-journal assembling clearances are uneven in one bearing, or inconsis-tent relationship of assembling clearances are encountered among all the bearings. Consideringthe structural characteristics of a TPJB, a concept named as "pad pair pre-load coefficient" corre-sponding to bearing pre-load coefficient is proposed. Firstly, the influence of bearing pre-load coef-ficient and pad pair pre-load coefficient on shaft vibration in a Jeffcot rotor is analyzed. Then takingNo.1 unit with two TPJBs in Guangzhou pumped storage power plant (GPSP) as an example, theinfluence of inconsistent relationship of the two bearing pre-load coefficients on shaft vibration isanalyzed. The results show that variety of one bearing pre-load coefficient will only influence vibra-tion amplitude, not involving the shape of shaft center orbit. But variety of one or more "pad pairpre-load coefficient" will influence not only vibration amplitude, but also the shape of orbit-whichwill be turned from a circle to an ellipse. By investigating variation characteristics of shape andvibration amplitude of orbits at the TPJBs, some theoretical bases will be supplied for diagnosingthe condition of the unit bearings.