Bending Creep and Stress Relaxation of Ti3AlC2 at High Temperature

2007 ◽  
Vol 280-283 ◽  
pp. 1373-1378 ◽  
Author(s):  
Yi Wang Bao ◽  
Yan Chun Zhou
Keyword(s):  
High Temperature ◽  
Stress Relaxation ◽  
Crack Growth ◽  
Threshold Value ◽  
Creep Process ◽  
Creep Failure ◽  
Bending Tests ◽  
Three Point Bending ◽  
Creep And Stress Relaxation ◽  
Increasing Temperature

Creep and stress relaxation of Ti3AlC2 were investigated using three-point bending tests at 800-1200°C under various load levels. The results show that the creep rate significantly increases with increasing temperature in the rang of 1000-1200°C. Subcritical crack growth during the creep process was found to be the main failure mechanism, i.e., the stress intensity factor increases with the creep-induced crack growth and results in the ultimate fracture. The lower limit of stress relaxation was considered as the threshold value of zero-creep stresses, and the ratio of the threshold stress to the applied stress was defined to be a parameter of creep resistance for estimating deformation behavior at high temperature. SEM examination confirmed that the creep failure in Ti3AlC2 was governed by such a damage evolution: cavitation ® crack initiation ® crack extension ® fracture.

scholarly journals Fractal Dimension of Fracture Surface in Rock Material after High Temperature

2015 ◽  
Vol 2015 ◽  
pp. 1-6 ◽  
Author(s):  
Z. Z. Zhang
Keyword(s):  
Fractal Dimension ◽  
Electron Microscope ◽  
High Temperature ◽  
Fracture Surface ◽  
Scanning Electron Microscope ◽  
Fractal Dimensions ◽  
Threshold Value ◽  
Fracture Surfaces ◽  
Increasing Temperature ◽  
Scanning Electron

Experiments on granite specimens after different high temperature under uniaxial compression were conducted and the fracture surfaces were observed by scanning electron microscope (SEM). The fractal dimensions of the fracture surfaces with increasing temperature were calculated, respectively. The fractal dimension of fracture surface is between 1.44 and 1.63. Its value approximately goes up exponentially with the increase of temperature. There is a quadratic polynomial relationship between the rockburst tendency and fractal dimension of fracture surface; namely, a fractal dimension threshold can be obtained. Below the threshold value, a positive correlativity shows between rockburst tendency and fractal dimension; when the fractal dimension is greater than the threshold value, it shows an inverse correlativity.

scholarly journals PROPERTIES OF COMPOSITIONAL MATERIALS BASED ON THE MIXTURES OF EPOXY POLYMERS AND OLIGOSULPHONES. PART 2. STATIC AND DYNAMIC RELAXATION PROPERTIES

2019 ◽  
Vol 4 (5) ◽  
pp. 140-146 ◽  
Author(s):  
Ю. Кочергин ◽  
Yuriy Kochergin ◽  
Т. Григоренко ◽  
Tatyana Grigorenko ◽  
В. Золотарева ◽  
...  
Keyword(s):  
Molecular Weight ◽  
High Temperature ◽  
Stress Relaxation ◽  
Dynamic Shear Modulus ◽  
Dynamic Shear ◽  
Dynamic Relaxation ◽  
Relaxation Properties ◽  
Epoxy Polymers ◽  
Creep And Stress Relaxation ◽  
Epoxy Systems

The effect of low-molecular polysulfones (oligosulfones) on the static and dynamic relaxation properties of epoxy polymers based on industrial resin ED-20 is studied. It is established that the modification of oligosulfones with terminal carboxyl, phenolic groups and a molecular weight from 1200 to 44500 leads to the formation of epoxy systems with higher performance in terms of development of static processes of creep and stress relaxation. It is demonstrated that the dynamic shear modulus increases with the introduction of the modifier. The magnitude of this effect is proportional to the molecular weight of oligosulfones. The intensities of the high-temperature α-transition at 390 K and the low-temperature β-transition at 208 K decrease with the introduction of the modifier. The improvement of the relaxation properties is associated with an increase in the density of the chemical grid of the epoxy matrix with the introduction of modifiers, its saturation with more rigid and heat-resistant component and the formation of additional intermolecular bonds between the components of the system

Oxidation Resistance and Bending Strength at High Temperatures of Ni/(ZrO2+Al2O3) Hybrid Materials

2018 ◽  
Vol 922 ◽  
pp. 104-109
Author(s):  
Hai Vu Pham ◽  
Makoto Nanko ◽  
Wataru Nakao
Keyword(s):  
High Temperature ◽  
Oxidation Resistance ◽  
Cross Section ◽  
High Temperatures ◽  
Room Temperature ◽  
Bending Strength ◽  
Bending Tests ◽  
Three Point Bending ◽  
Order Of Magnitude ◽  
Zone Development

Oxidation resistance and bending strength at high temperatures of 5 vol% Ni/(10 vol% ZrO2+Al2O3) were investigated in this paper. Oxidation tests were conducted at temperature ranging from 1100 to 1300oC for 1 to 24 h in air. The oxidation resistance of the composites was studied via observation of oxidized-zone development from a cross-section view after oxidation. Three-point bending tests were conducted at temperatures ranging from room temperature to 1200oC in order to estimate its performance at high temperatures. Bending strength of the composites achieved 1200 MPa at room temperature and 460 MPa at 1200oC. Dispersion of ZrO2in Ni/Al2O3composites enhanced both their room and high temperature bending strength. Nevertheless, ZrO2slightly degraded the oxidation resistance of the composites. The oxidation rate of Ni/(ZrO2+Al2O3) was one order of magnitude higher than that of Ni/Al2O3.

THE EFFECT OF HIGH TEMPERATURE CORROSION ON MECHANICAL BEHAVIOR OF A GAMMA-TiAl ALLOY

2010 ◽  
Vol 24 (15n16) ◽  
pp. 2970-2975 ◽  
Author(s):  
WENYUE ZHAO ◽  
YUE MA ◽  
SHENGKAI GONG
Keyword(s):  
High Temperature ◽  
Fracture Behavior ◽  
Tial Alloy ◽  
Crack Nucleation ◽  
High Temperature Corrosion ◽  
Bending Tests ◽  
Three Point Bending ◽  
Salt Corrosion ◽  
Corrosion Pits ◽  
Bending Fracture

The mechanical properties of Ti -48 Al -2 Cr -2 Nb alloy were discussed after the high temperature corrosion tests carried out with salt mixture of 75wt. % Na 2 SO 4 and 25wt. % NaCl at 800°C. The microstructure of the alloy after corrosion was observed by SEM and the fracture behavior of the corroded and uncorroded alloys was investigated by means of the three-point bending tests. It has been shown that the corrosion path was mainly along the lamellar structure and rough surface with a large number of corrosion pits formed during the high temperature corrosion. The experimental results also indicated that the bearing capacity of bending fracture descended evidently due to the molten salt corrosion at high temperature, which only had remarkable effects on the surface state of the alloy. The microcracks inside the alloy always propagated along the phase interfaces and grain boundaries while the corrosion pits on salt-deposited surface became the main crack initiation location in corroded alloy. The stress concentration caused by corrosion was considered as the essential reason of the property reduction, which decreased the energy barrier of crack nucleation and shortened the incubation period.

On the measurement of the activation energies for creep and stress relaxation

1964 ◽  
Vol 281 (1385) ◽  
pp. 258-273 ◽  
Keyword(s):  
Stress Relaxation ◽  
Temperature Dependence ◽  
Activation Energies ◽  
Real Component ◽  
Boundary Relaxation ◽  
Creep And Stress Relaxation ◽  
The Many ◽  
Increasing Temperature ◽  
True Values ◽  
Snoek Relaxation

A theory is proposed which enables activation energies for creep (Δ H c ), and stress relaxation (Δ H s,r ) to be calculated when the limiting moduli vary with temperature. The theory explains the agreement obtained by Kê between Δ H c , Δ H s.r. and the activation energy for internal friction Δ H i, f. for the grain boundary relaxation in aluminium . The theory rectifies the existing discrepancy between Δ H c (or Δ H s.r. ) for the β -relaxation in polymethyl methacrylate ( PMMA ) and Δ H i.f. . The discrepancy is shown to be due to the assumption that G U and G R , the unrelaxed and relaxed moduli, do not vary with temperature. It is eliminated by assuming that both limiting moduli have the same finite temperature dependence. This temperature dependence is obtained from measurements of the real component of the shear modulus G '(ω) at 3·3 x 10 4 c/s on the assumption that in the β -region ( — 50 to 20 °C) and at this frequency the temperature dependencies of G '(ω) and G U are the same. It is probable that the many previous determinations of Δ H c and Δ H s.r. for rigid polymers exceed the true values by amounts of the order of 70%, the discrepancy in PMMA . The theory is also used to determine Δ H s.r. for a Snoek relaxation for which G U decreases and G R increases with increasing temperature. The result obtained for oxygen in tantalum is Δ H s.r. = 27 kcal/mole in agreement with Δ H i.f. .

scholarly journals Effect of Post-Cure on the Static and Viscoelastic Properties of a Polyester Resin

Polymers ◽  
2020 ◽  
Vol 12 (9) ◽  
pp. 1927
Author(s):  
Marco P. Silva ◽  
Paulo Santos ◽  
João M. Parente ◽  
Sara Valvez ◽  
Paulo N. B. Reis ◽  
...  
Keyword(s):  
Stress Relaxation ◽  
Room Temperature ◽  
Bending Strength ◽  
Polyester Resin ◽  
Thermal Characterization ◽  
Unsaturated Ester ◽  
Bending Properties ◽  
Scanning Calorimetry ◽  
Bending Tests ◽  
Three Point Bending

This work intends to study the effect of the curing parameters on the mechanical properties of a polyester resin without a complete curing reaction process. For this purpose, cures at room temperature, 40 °C, and 60 °C, and post-cures at 40 °C and 60 °C, with different exposure times, were considered. Three-point bending tests were performed to assess the bending properties and both stress relaxation and creep behavior. The degree of crosslinking was estimated by evaluating the C = C ester bond, by Fourier infrared spectroscopy and complemented with the thermal characterization made by differential scanning calorimetry. The results showed that higher curing temperatures are preferable to methods involving curing and post-curing, which can be confirmed by the higher degree of conversion of unsaturated ester bonds at 60 °C. Compared to the resin cured at room temperature, the bending strength increased by 36.5% at 40 °C and 88.6% at 60 °C. A similar effect was observed for bending stiffness. In terms of stress relaxation and creep strain, the lowest values were obtained for samples cured at 60 °C.

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