Characterization of Failure Mechanisms of Duplex and Graded Thermal Barrier Coatings Exposed to Thermal Shock Test

The beginning of failure of a (ZrO2-7%Y2O3)/(Ni-22%Co-17%Cr-12.5%Al-0.6%Y) duplex andgraded coating systems on lnconel 617 and IN738LC in burner rig tests has been characterized.The test conditions are 40 s heating up to 75O℃ substrate temperature followed by 80 s aircooling. Failure is considered at the appearance of the first bright spot during heating period.Stresses due to thermal expansion mismatch strains on cooling are the probable cause of life-limiting in this conditions of testing.

Blast response of clay brick masonry unit walls unreinforced and reinforced with polyurea elastomer

Clay brick masonry unit(CBMU) walls are widely used in building structures,and its damage and protection under explosion loads have been a matter of concern in the field of engineering protection.In this paper,a series of full-scale experiments of the response characteristics of 24 cm CMBU walls unreinforced and reinforced with polyurea elastomer subjected to blast loading were carried out.Through setting 5.0 kg TNT charges at different stand-off distances,the damage characteristics of masonry walls at different scaled distances were obtained.The reinforcement effect of different polyurea coating thicknesses and methods on the blast resistance performance of masonry walls under single and repeated loads were also explored.Five failure grades were summarized according to the dynamic response features of masonry walls.Based on the stress wave propagation pattern in multi-media composite structures,the internal stress distribution of masonry walls were analyzed,and the division basis of the masonry walls’ failure grades was then quantified.Combined with Scanning Electron Microscope(SEM)images,the deformation characteristics of soft and hard segments of polyurea and effects of detonation products on microstructures were revealed respectively,which provides an important reference for the design and application of polyurea in the blast resistance of clay brick masonry walls.

Triaxial shear behavior of a cement-treated sand——gravel mixture

A number of parameters,e.g.cement content,cement type,relative density,and grain size distribution,can influence the mechanical behaviors of cemented soils.In the present study,a series of conventional triaxial compression tests were conducted on a cemented poorly graded sandegravel mixture containing 30% gravel and 70% sand in both consolidated drained and undrained conditions.Portland cement used as the cementing agent was added to the soil at 0%,1%,2%,and 3%(dry weight) of sandegravel mixture.Samples were prepared at 70% relative density and tested at confining pressures of 50 kPa,100 kPa,and150 kPa.Comparison of the results with other studies on well graded gravely sands indicated more dilation or negative pore pressure in poorly graded samples.Undrained failure envelopes determined using zero Skempton’s pore pressure coefficient (= 0) criterion were consistent with the drained ones.Energy absorption potential was higher in drained condition than undrained condition,suggesting that more energy was required to induce deformation in cemented soil under drained state.Energy absorption increased with increase in cement content under both drained and undrained conditions.