Short-term Static Strength Research Articles

Mathematical model of short-term static strength of the overlap joint from low carbon steel brazed with tin

ABSTRACT A mathematical model of a brazed joint strength consisting of position and scattering characteristics is introduced. Random and residual errors are taken into account for the scattering characteristics. It is shown that the nature of the error distribution relative to the position characteristics must be considered using untruncated and truncated distribution functions. The lower confidence limit of the destructive stresses of the joint made of steel St3 and brazed with tin is determined, with a confidence coefficient of 0,95 and the upper limit of the stress allowance for a brazed joint with a safety factor of 1,5.

Influence of the asphalt pavement on the short-term static strength and long-term behaviour of RC slabs strengthened with externally bonded CFRP strips

Abstract Lateral cantilevers of Reinforced Concrete (RC) box-girder bridges might have a lack of negative bending resistance in cross-direction due to the increase of traffic loads or the degradation along the time of the material properties. Externally Bonded (EB) Carbon Fiber Reinforced Polymer (CFRP) strips on the top side of these bridge slabs are a possible strengthening technique for such purpose. The paper presents a study regarding the short- and long-term behaviour of such reinforcements where the specific case of a lateral cantilever element is investigated. Strengthening of negative bending moments on the upper deck side implicates the exposure of the composite reinforcement to both short- and long-term elevated temperature scenarios. During the construction phase, the application of warm mastic asphalt induces elevated peak temperatures in the epoxy resin of about 80 °C with a subsequent slow cooling phase over several hours. In this investigation, the temperature evolution on several locations was measured. Then, the short-term residual bond strength of the strengthened system after such an exposure is checked with both lap-shear and large-scale tests. The long-term behaviour with the seasonal temperature fluctuation is another concern. For this purpose, a cantilever slab with a real asphalt layer under sustained load was installed and continuously monitored in time over one year.

Use of tungsten single crystals to enhance nuclear reactors structural elements properties

Abstract This paper demonstrates advantages of using tungsten single crystal as structural material in science absorbing industry in comparison with polycrystalline material. High-temperature short-term static strength and creep resistance characteristics of polycrystalline tungsten and single crystal alloy were obtained and compared. The results of comparative studies of the mechanical properties of polycrystalline and monocrystalline tungsten – 4% tantalum alloy are presented. It is shown that monocrystalline tungsten based materials have both high-temperature strength and plasticity which makes them most suitable for use under high temperatures and high mechanical stresses. Use of monocrystalline tungsten as a structural material makes it possible to prolong the service life and avoid the failures resulting from embrittlement and strain. Moreover, thermo mechanical treatment of monocrystalline tungsten enhances its high-temperature strength. However, it is necessary to carry out additional experimental research to choose the appropriate thermo mechanical treatment conditions.

Temperature dependences of the mechanical properties of austenitic and martensitic steels in hydrogen

The influence of gaseous and preliminarily dissolved hydrogen on the characteristics of short-term static strength, crack resistance, and low-cycle durability of martensitic and austenitic steels is studied within the temperatures range 293–1073°K, under pressures of hydrogen varying within the range 0–35 MPa, for the strain rates of 0.01–100 mm/min, and the strain amplitudes of 0.8–1.6%. We determine the loading rates and the conditions of action of hydrogen leading the maximum possible hydrogen degradation of each material. The influence of the chemical composition and structural state on the degree of embrittlement and fractographic features of the fracture of steels in the presence of hydrogen is analyzed.

High-temperature characteristics of low-alloyed molybdenum alloy VM-1

The short-term static strength and momentary creep characteristics of low-alloyed molybdenum alloy VM-1 are investigated in the temperature range from 1820 to 2270 K. The creep strength values for the alloy were obtained for residual strain tolerances of 0.5 and 1.0%, the test durations of 102, 103, and 104 s at temperatures of 1820, 2120 and 2270 K. The empirical functional dependence is proposed to describe the correlation relation between the characteristics of short-term static strength, plasticity and momentary creep of the material in the thermomechanical range under study.

On the hardening effect of plasma-deposited coatings

We studied the influence of plasma-deposited titanium-nitride coatings on the characteristics of short-term static strength of the matrix material. In the process of deposition of these coatings, we observed an increase in the conventional yield limit and ultimate strength of the material accompanied by a decrease in the characteristics of plasticity.

An approximate model of predicting the anisotropy of high-cycle fatigue strength of composite materials

1. We proposed a calculation-empirical model for the approximate evaluation of the anisotropy of the high-cycle fatigue strength of the CMs which takes into account simultaneously the variation of loading frequency and type of deformation. In the experimental part, the complete model requires determination of fatigue strength in respect of nonzero pulsed tensile loading and compression in the orthogonal reinforcement directions and under the angle Φ=45°, and in the simpler variant only in the preferential reinforcement direction (Φ=0°). For calculations it is necessary to obtain experimental data on the anisotropy of the limit of the short-term static strength and also long-term static strength in tension and compression in the reinforcement directions. 2. The results show that the calculated and experimental data for the woven and oriented glass fiber-reinforced plastics in pulsed tension, compression, and symmetric tension-compression in the directions Φ=15, 30, 45, and 90° are in satisfactory agreement.

Effect of temperature and test conditions on the mechanical properties of molybdenum alloy 4604 in different structural conditions

Molybendum and its alloys, exhibiting high-temperature strength and satisfactory ductility characteristics at room and reduced temperatures, are currently finding extensive industrial use as structural materials for manufacturing critical machine components and assemblies operating under severe thermal and force loading schedules. Results are presented over a range of 20-2250/sup 0/C of short-term static strength properties for alloy 4604 in the Mo-V-C system. Strength and ductility characteristics were determined in VTU-2V equipment in a vacuum of 0.1 MPa on cylindrical proportional specimens with a gage diameter of 3 and 4 mm and a gage length of 15 and 20 mm. It has been established that conditions for carrying out high-temperature short-term static tests on alloy 4604 (heating rate, duration of high-temperature stabilizing soaking of a specimen before loading, strain rate) have a marked effect on experimental results. Annealing for 1 h at 1200, 1500 and 1600/sup 0/C sharply reduces the strength indices for alloy 4604, and increases ductility in the range 20-1500/sup 0/C. Above 1500/sup 0/C the mechanical properties of the alloy are independent of its structural condition. For material subjected to high-temperature annealing, they shift by approximately 250/sup 0/C into the lower-temperature region compared with that for material in the workedmore » condition.« less

Laws of surface crack growth in alloy AMtsS during low-cycle loading

1. Alloy AMtsS specimens with a crack fracture under low-cycle loading after three stages of fatigue crack growth: elastic crack growth (rp 10, δ>0.1 mm). 2. The fracture of flat-rolled structural elements made of alloy AMtsS with surface cracks is quasistatic under conditions of axial low-cycle loading. 3. The nominal net stress equal to the yield strength is a criterion of the transition from elastic-plastic to quasistatic crack growth in alloy AMtsS under low-cycle loading. 4. Crack opening equal to the critical crack opening in short-term static strength tests,\(\delta _{c_s } = \delta _{c_c } \), is a criterion of unstable growth of surface cracks in alloy AMtsS under low-cycle loading.

Mechanical properties of plastics reinforced with silicon carbide

1. It has been established that the short-term static strength of silicon carbide fibers follows a normal distribution law. 2. Young's modulus obtained from the additivity law for the direction of reinforcement of unidirectional and biaxially reinforced (1:1) SCRP agrees satisfactorily with the experimental value. 3. The strength of the fibers used governs the strength properties of the composites and is used (at 80–90%) in the optimum technology of creating a material. 4. The impact strength of plastics containing silicon carbide fibers is 7–14 kgf·cm/cm2 and the fatigue strength for pulsed flexure is approximately 0.45 of the static flexural strength.