Temperature Tensile Stress Research Articles

The effect of networks cracks on the strength of pavement

The analysis of the methodology for determining the coefficient of strength of pavement, based on the results of a visual assessment of the condition of pavement is performed. The traditional classification of the networks of cracks is considered, and the reasons for their arising on the Bolshie Uki - Znamenskoe road are analyzed. Traditional fatigue cracking and temperature tensile stresses are defined as main causes of cracks network. The feature of the emergence of networks of cracks on the pavement of the road Bolshie Uki - Znamenskoe, which consists in the appearance of these defects in sectors located on terrain with long standing groundwater, is revealed. Therefore, as a related cause of the appearance of a network of cracks, the effect of insufficient strength of a subgrade of cohesive soils and increased humidity was noted. Experimental work was carried out to determine the elastic deflections in the sectors with networks of cracks and the reference sector without defects. According to the experimental work, safety factors are determined, and mathematical models of the dependence of the coefficient of strength from the cell size of the cracks network are developed.

Determination of quasi-static and residual stresses in the course of the thermoplastic hardening in a boundary layer of the material

In order to induce residual compressive stresses in the boundary layer of a steel plate heated to temperature T0 = 600 °C, a method of jet water cooling with time-varying heat transfer coefficients is considered. By solving the corresponding heat conduction problem, it is shown that the maximum temperature difference between the surface and the center of a 2 mm thick plate is 105 °C. It is observed within 0.02 s since the start of cooling, the time of its complete cooling is equal to 0,32 s. Calculations of temperature stresses using the finite element method showed that temperature tensile stresses occur on the outer surface of the plate. They may reach 26 kg/mm2 which exceeds the yield strength of this material. As a result of plastic deformation, the thermal tensile stress relieving occurs in the course of cooling of the plate surface layer; when it is completely cooled, the residual compressive stresses 21.8kg/mm2. (on the surface of the plate) are induced in this layer (0,25 mm depth).

Liftoff of single crystal diamond by epitaxial lateral overgrowth using SiO2 masks

We describe a method that allows an easy separation of a single crystal diamond layer grown by homoepitaxy in a chemical vapour deposition (CVD) process from the growth substrate. In a first step a thin SiO2 layer is deposited on top of the seed crystal. This layer is patterned by photolithography and reactive ion etching (RIE) to obtain a mask with open windows and covered areas. In an epitaxial lateral overgrowth (ELO) process diamond is grown homoepitaxially through the free window areas and laterally across the covered areas until the mask is completely covered by diamond. During cool down from deposition temperature tensile stress σzz perpendicular to the growth surface is formed in the diamond bridges grown in the window areas. The absolute value of the stress depends on growth temperature, difference in coefficients of thermal expansion (CTE) between diamond and the specific mask material and finally on the fill factor (FF). The stress amplitude can reach more than +2 GPa and stress intensity factors in the range of typical fracture toughness values reported for single crystal diamond. Our experiments demonstrate that an immediate crack formation can be achieved which facilitates an easy separation between the CVD grown diamond layer and the seed crystal. The described concept develops its highest potential with increasing lateral dimensions of the seed wafers.

Effect of nano-sized ZrO2 on high temperature performance of Mo-ZrO2 alloy

Mo-ZrO2 alloys were prepared through hydrothermal synthesis and powder metallurgy process. Room temperature microstructures of these alloy plates were observed, while high temperature tensile strength and plasticity of them were tested above 1000 °C using a Gleeble-1500D thermal simulated test machine. Results have shown that ZrO2 particles were fine in the alloy and distributed at grain boundaries and within the grains. The second phase of ZrO2 particles demonstrated a pinning effect to retard recrystallization progress and thus enhance high temperature tensile stress and plasticity of the alloys effectively. Besides, the strengthening effect of the second phase in the alloy could also effectively improve its high temperature tensile stress. Under 1400 °C, maximum tensile stress of Mo-1.5%ZrO2 alloy was 1.5 times that of pure molybdenum, while the alloy plasticity also increased dramatically. The area shrinkage of Mo-1.5% ZrO2 alloy at 1400 °C was 5 times that of pure molybdenum.

OPTIMIZATION OF THE TEMPERATURE CONTROL SCHEME FOR ROLLER COMPACTED CONCRETE DAMS BASED ON FINITE ELEMENT AND SENSITIVITY ANALYSIS METHODS

Achieving an effective combination of various temperature control measures is critical for temperature control and crack prevention of concrete dams. This paper presents a procedure for optimizing the temperature control scheme of roller compacted concrete (RCC) dams that couples the finite element method (FEM) with a sensitivity analysis method. In this study, seven temperature control schemes are defined according to variations in three temperature control measures: concrete placement temperature, water-pipe cooling time, and thermal insulation layer thickness. FEM is employed to simulate the equivalent temperature field and temperature stress field obtained under each of the seven designed temperature control schemes for a typical overflow dam monolith based on the actual characteristics of a RCC dam located in southwestern China. A sensitivity analysis is subsequently conducted to investigate the degree of influence each of the three temperature control measures has on the temperature field and temperature tensile stress field of the dam. Results show that the placement temperature has a substantial influence on the maximum temperature and tensile stress of the dam, and that the placement temperature cannot exceed 15 °C. The water-pipe cooling time and thermal insulation layer thickness have little influence on the maximum temperature, but both demonstrate a substantial influence on the maximum tensile stress of the dam. The thermal insulation thickness is significant for reducing the probability of cracking as a result of high thermal stress, and the maximum tensile stress can be controlled under the specification limit with a thermal insulation layer thickness of 10 cm. Finally, an optimized temperature control scheme for crack prevention is obtained based on the analysis results.

Fracture Research on Preheating Installation of Directly Buried Heating Return Water Pipe with Large Diameter

Pipe fracture and compensator tear may happen when directly buried pipes with large diameter, high temperature and pressure adopt preheated installation. Combined with engineering, this paper analyzes theoretically the fracture accident on DN1200 return water pipe during the period of cold operation and analyzes various factors which cause the pipeline fracture, when adopt open ditch electric preheating. By the numerical simulation, the size of influence factors on fracture was obtained, and the conclusion that the tensile stress is greater than the compressive stress was also obtained, where the preheating temperature was defined by means of “intercycle temperature”. It is worth nothing, the buried pipeline will emerge vertical bending under the main impact of soil and transportation loads. The vertical bending is related to pipe base, and the value of curving stress will be very big if the pipe base is mishandled. The coupling effect of curving stress and the temperature tensile stress can lead the pipeline to fracture, such as the disposable compensator place, the pipeline welding place, corners, the pipe wall flaw place and so on. This paper proposed the effective preventive measure which may reduce the occurrence probability of pipeline fracture during temperature drop process.

Macroscopic and nanometer scale stress measurement of Ni(Pt)Si silicide: Impact of thermal treatments ranging from millisecond to several hours

The authors have measured and compared the stress in nickel silicide full sheet layers prepared with added platinum on (001) p-type Si wafers by using either a rapid thermal anneal (RTA) at 390 °C or a millisecond submelt laser dynamic scanning anneal (DSA) at 800 °C. The room temperature tensile stress of the silicide annealed with DSA is 1.65 GPa, whereas that of the silicide annealed with RTA at 390 °C is 800 MPa. Our analysis confirms that the origin of the stress lies in thermal expansion factors. Despite some small variations, the stress remains highly tensile in both layers after a 1 h post-treatment at 400 °C, with values of 1.4 GPa and 850 MPa for the DSA and RTA samples, respectively. The authors also performed strain measurements with dark field electron holography in the source drain region of 28 nm field complementary metal oxide semiconductor field effect transistors, under the silicide dot. They then determined the stress inside the silicide by combining the strain measurement with finite element mechanical simulations; values of 1.5 GPa and 600 MPa were found at the nanometer scale for the DSA and RTA samples, respectively, which are consistent with the macroscopic observations.

Tensile Behavior of 2.5D C/SiCN Composites

Tensile behavior of C fiber reinforced amorphous SiCN ceramic matrix composites (C/SiCN ) were investigated by tensile machine. The microstructure morphologies were observed by scanning electron microscope. The results indicate that the tensile stress-strain curves of C/SiCN composites dispaly typical elastic deformation and cracks propagation stages. The 1500°C pre-sabilization treatment of C/SiCN in vacuum facilitates room temperature tensile stress growth. The higher treated temperature such as 1900°C is yet opposite. The reasons were attributed to thermal stress relaxation of C/SiCN after pre-stabilization treatment in vacuum.

The Control Study of Mass Concrete Floor Temperature Crack

Analysis the factors of mass concrete temperature crack. Combined with the Nan Yang Branch of CUCC cement clinker production line of the second phase of mass concrete construction, it proposed some measures about how to prevent the temperature stress crack of mass concrete due to hydration heat of cement generated temperature difference .By controlling the temperature of the concrete strictly, decreasing the temperature difference between inside and outside, preventing shrinkage joint, reducing the slump loss, delaying setting time, etc. To ensure from the construction maintaining process of mass concrete foundation floor, the tensile strength of concrete is always greater than the maximum temperature tensile stress to prevent temperature cracks appear ensure the quality of mass concrete construction.

Influence of Reinforcement on Temperature and Stress of Hollow Pier

This paper put circular hollow bridge pier under cold wave as an example. Based on solid heat conduction principle, we selected its border and initialized condition according with actual circumstance. Combining solid heat conduction differential equation and generalized hooke’s law which takes temperature stress into account, we have calculated the temperature and stress of concrete piers with different reinforcement ratio by ANSYS finite element software. These results indicate that the longitudinal bars and horizontal ring stirrups in concrete circular hollow pier under cold wave will increase its outer surface temperature tensile stress. Namely the reinforcements in concrete circular hollow pier not only do not prevent its outer surface cracks under the action of cold wave, but will also promote the surface cracks to produce faster. Therein, the contribution of horizontal ring stirrups to the surface cracks is greater than the longitudinal bars.

Application of Ductile Fracture Criterion in Hot Forging Damage of Mn18Cr18N Steel

In this paper, the hot forging behavior of Mn18Cr18N steel is studied based on the viewpoint of meso-damage. According to high temperature tensile stress - strain curve of Mn18Cr18N steel under different temperatures, the relationships of void initiation strain and fracture strain with deformation temperature are obtained. The temperature dependence of damage threshold is obtained at 950°C~1200°C for Mn18Cr18N steel by Cockcroft & Latham criterion, That is, Ci,f value increases monotonously with temperature increasing. The corresponding deformation amounts of void initiation and fracture appearing are predicted accurately by combining Cockcroft & Latham criterion with finite element analysis during hot forging of Mn18Cr18N steel, which is in good agreement with the actual production. Under these experimental conditions, once upsetting deformation amount should be controlled in 50% based on hot upsetting test and finite element simulation. These provide theoretical instruction for preventing forging cracking of Mn18Cr18N steel.

Temperature dependence of in-plane stresses in sublayers of Al/AlN/Al 2O 3(0 0 0 1) structure

Al and AlN sublayers with thickness of 100 and 500 nm, respectively, deposited on sapphire using pulsed laser ablation are characterized by elevated-temperature X-ray diffraction. Pole figure measurements performed at room temperature indicate heteroepitaxial growth of Al on AlN and AlN on sapphire with Al(1 1 1)[1 1 ̄ 0]|| AlN(0 0 0 1)[1 1 2 ̄ 0 ] and AlN(0 0 0 1)[1 0 1 ̄ 0]|| Al 2 O 3 (0 0 0 1)[1 1 2 ̄ 0 ] , respectively. The diffraction measurements in the temperature range of 25–550°C allow to resolve in-plane residual stresses for both sublayers simultaneously. The heating up of the structure is accompanied by a decrease of room temperature tensile stress and a subsequent plastic deformation in Al sublayer in the temperature range of 350–550°C while, in the AlN sublayer, a decrease of room temperature compressive stress as well as a post-annealing stress relaxation are observed. The temperature behavior of the stresses in the structure can be interpreted by the mismatch of thermal expansion coefficients between sublayers and substrate.

Initial hillock formation and changes in overall stress in Al–Cu films and pure Al films during heating

The effect of adding a few percent (3 at.%) Cu to Al films on the initial hillock formation and the changes in overall film stress were studied. Al films were evaporated by an electron-beam gun onto Si wafers in an ultrahigh vacuum deposition system and Al–Cu films were coevaporated with a thermally heated source used for the Cu. The as-deposited samples were radiatively heated at 3 °C/s in an air environment. During heating, the initial hillocking and the changes in overall stress were measured simultaneously and in real time with a specially designed optical instrument. The measurement principle of this instrument is based on laser beam deflection, caused by wafer bending due to film stress, and collection of the laser light scattered off from the hillocks appearing on the film surface. The experimental results show that Cu alloying has a strengthening effect on Al films, resulting in delayed and considerably reduced hillock formation. Before heating, the as-deposited Al–Cu samples were investigated by total integrated scattering and atomic force microscopy. These investigations showed that Al–Cu films are considerably smoother and have smaller grains than Al films of similar thickness (340 nm). It was found that the small grains of Al–Cu films contribute to increasing the tensile stress–temperature slope. In addition, Al–Cu films can withstand higher compressive stresses than Al films.

Temperature Effects on Cellular Rigid Pavement Compared to Flat Slabs

Temperature effects on rigid pavements have been shown to be significant fatigue contributors in combination with stresses produced by load, particularly at slab corners. A construction method for rigid pavement utilizing waste plastic forms to create dome-shaped cells in an orthogonal array was analyzed for stresses resulting from the application of a standard highway equivalent single axle load (ESAL). In this paper, cellular rigid pavement (CRP) is analyzed to compare temperature effects using the finite-element method. Bottom temperature tensile stresses are significantly lower for CRP than for the comparable solid slab, and in combination with load tensile stresses, vary from slightly higher to very much lower. Top tensile stresses due to temperature exceed the slab strength in the solid slab while top stresses are not significant in the CRP slab. The application of CRP appears to mitigate to a considerable extent the fatigue effect of temperature stresses in pavement of equal thickness to that of so...

Stress reduction of gold absorber patterns on x-ray masks

A resonance frequency measurement technique has been used to measure the stress at temperature of plated gold films on x-ray mask membranes over the temperature range of 90–525 K. Room temperature tensile stress increases are observed after above room temperature anneals. Stress relaxations are measured after liquid nitrogen cools. The tensile stress increases and the stress relaxations depend upon the microstructure of the plated films. Focused ion beam imaging shows that grain growth is the dominant mechanism for the tensile stress increases observed for fine grained as-plated gold films.

Stresses in SiO2 Films Obtained from the Thermal Decomposition of Tetraethylorthosilicate—Effect of Heat‐Treatment and Humidity

The interference fringe method was used for measurement of stresses in films deposited on Si and Ge substrates. An attempt has been made to deduce both the amount of stress resulting from intrinsic stress and the stress arising from mismatch of temperature coefficient of expansion. From measurement at room temperature of stress in films deposited by thermal decomposition of tetraethylorthosilicate at 725°C in forming gas , or at 450°C in oxygen , it is concluded that the intrinsic stress is tensile. The mechanical properties of the films prepared by these two methods were assumed to be similar to those of bulk vitreous silica. An explanation is offered for the observed increase in the room temperature tensile stress of the film on heat‐treatment to 700°C, and to the following decrease in tensile stress on heat‐treatment to 800°C. A decrease in the room temperature stress in the film occurs on exposure of the film to a humid ambient.