Piezoelectric properties of low loss and high Curie temperature (Bi, La)FeO_3-Pb(Ti, Mn)O_3 ceramics with Mn doping

Piezoelectric ceramics of 0.6(Bi0.9La0.1)FeO3-0.4Pb(Ti1-xMnx)O3 (BLF-PTM) for x=0, 0.01, 0.02, and 0.03 were prepared by sol-gel process combined with a solid-state reaction method. The tan? for BLF-PTM of x=0.01 is just 0.006 at 1 kHz, drastically decreasing by using Mn dopants. The TC increases to 490 ℃ for BLF-PTM of x=0.02. Furthermore, Mn modification effectively enhances the poling state and the piezoelectric properties of BLF-PTM. The kp, Qm, d33, and g33 of 0.34, 403, and 124 pC1·N-1 and 37×10-3 Vm·N-1 are achieved for BLF-PTM of x=0.01. The results indicate that Mn modified BLF-PTM is a competitive high power and high temperature piezoelectric material with excellent piezoelectric properties.

Effect of Cu addition on overaging behaviour,room and high temperature tensile and fatigue properties of A357 alloy

The aims of the present work are to evaluate the overaging behaviour of the investigated Cu-enriched alloy and to assess its mechanical behaviour,in terms of the tensile and fatigue strength,at room temperature and at 200℃,and to correlate the mechanical performance with its microstructure,in particular with the secondary dendrite arm spacing(SDAS).The mechanical tests carried out on the overaged alloy at 200℃ indicate that the addition of about 1.3 wt.%Cu to the A357 alloy enables to maintain ultimate tensile strength and yield strength values close to 210 and 200 MPa,respectively,and fatigue strength at about 100 MPa.Compared to the quaternary(Al−Si−Cu−Mg)alloy C355,the A357−Cu alloy has greater mechanical properties at room temperature and comparable mechanical behaviour in the overaged condition at 200℃.The microstructural analyses highlight that SDAS affects the mechanical behaviour of the peak-aged A357−Cu alloy at room temperature,while its influence is negligible on the tensile and fatigue properties of the overaged alloy at 200℃.

Tensile and high-cycle fatigue properties of spray formed Al10.8Zn2.9Mg1.9Cu alloys after two-stage aging treatment

Based on the investigation of the tensile properties of spray formed ultra-high strength Al10.8Zn2.9Mg1.9Cu alloys, the high-cycle fatigue properties under different theoretical stress concentration factors were investigated, the fatigue fracture surfaces and microstructures were observed, and the fatigue mechanism was discussed. The results indicate that the ultimate tensile strength of spray formed Al10.8Zn2.9Mg1.9Cu alloys can reach up to 730?740 MPa, and the elongation is about 8%?10% under the condition of two-stage aging treatment. For the stress ratio is 0.1, the maximum stress for 107 cycles is over 400 MPa and 120 MPa, when the theoretical stress concentration factor is 1 and 3, respectively.

Effect of low cycle fatigue pre-damage on very high cycle fatigue

Carbon-manganese steel is often applied in components of pipes in nuclear plant. Ultrasonic fatigue tests following low cycle fatigue （LCF） cycles damaged are used to study the strength of very high cycle fatigure （VHCF）. The comparison of test results of simple VHCF and cumulative fatigue （LCF plus VHCF） shows that LCF load influences the following VHCF strength. Continuum damage mechanics model is extended to VHCF region.

Effect of Rare Earth Elements on Low Frequency Fatigue of Hot Rolled Steel 60CrMnMo at High Temperature

The effect of rare earth(RE) on low frequency high temperature fatigue strength of hot rolled steel 60CrMnMo was investigated. The results show that by adding a certain amount of RE in steel 60CrMnMo, its serviceable life during low frequency fatigue test at high temperature can be improved.The number of cycles for fracture was increased by 18.5%～28.8%. The number of large inclusion particleswas reduced and the composition of inclusions and their shape were changed as well. The strip distances on fatigue fracture surface were decreased. It is concluded that the optimum amount of RE addtion is about 0.05 wt%～0. 10 wt%.

EFFECT OF FABRICATION ON HIGH CYCLE FATIGUE PROPERTIES OF COPPER THIN FILMS

The influence of fabrication on the tensile and fatigue behavior of copper films manufactured by 3 kinds of fabrication methods was investigated. The tensile and high cycle fatigue tests were performed using the test machine developed by authors. Young＇s moduli （72, 71 and 69 GPa, respectively） are lower than the literature values （108-145 GPa）, while the yield strengths were as high as 358, 350 and 346 MPa, respectively and the ultimate strengths as 462, 456 and 446 MPa, respectively. There is not much difference in the tensile properties of the 3 kinds of films. There is little difference in the fatigue properties of the 3 kinds of films but one of them has shorter fatigue life than others in high cycle region and longer fatigue life than others in low cycle region.

A PROBABILISTIC ASSESSMENT OF TEMPERATURE EFFECTSON THE LOW CYCLE FATIGUE BEHAVIOUR OF 1Cr_(18)Ni_9Ti STEEL WELD METAL

Based on the test results obtained from the single-step test and the incremental-step test at room temperature and 240℃, a probabilistic assessment of temperature effects on the cyclic stress-strum response and the fatigue life of 1Cr18Ni9Ti steel weld metal is performed. In orber to assess the temperature effect on cyclic stress amplitude where there is a scatter of the material cyclic constitution, a probabilistic assessment approach on the basis of probabilistic modified Ramberg-Osgood relations is introduced.The investigation shows that the cyclic stress amplitude and the scatter of cyclic stress amplitude data are decreased at 240℃. Similarly, from the consideration of the fatigue life scatter a probabilistic assessment of temperature effect on the fatigue life is suggested on the basis of probabilistic Langer S-N relations. The investigation shows that the crack initiation life is increased and the scatter of crack initiation life data is decreased at 240℃.

Influence of welding on low cycle fatigue properties of Co-based superalloy FSX-414

Co-based superalloys such as FSX-414 have been recently used in gas turbine first stage nozzles. During service, nozzles are exposed to low cycle fatigue, which can lead to cracking of these components. The cracks on these nozzles are usually welded with ttmgsten arc welding （TIG） using Co-based filler metals. In this paper, the effect of TIG on the tensile and low cycle fatigue properties of Co-based superalloy FSX-414 was studied at 950℃. The experimental results show that the yield and ultimate tensile stresses of welded and unwelded specimens are comparable to each other. But toughness of welded specimens is lower than that of unwelded ones. The low cycle fatigue properties of FSX-414 were studied at a strain rate of 3.3×10^-4 s^-1, strain ratio R=-1 （R=emin/emax） and Aet （total strain change） from 0.8% to 2%. In welded specimens, at high strain cycling, the nucleation and growth of cracks occur in the welded zone. But at Aet=0.8%, fracture occurs in the same zones of unwelded specimens. The results show that the total fatigue lives of the welded specimens are shorter than those of unwelded ones. In all of the low cycle fatigue tests, softening phenomena are observed.

Low cycle fatigue behavior of high strength gun steels

The low cycle fatigue (LCF) behavior of two high strength steels, withnominal chemical compositions (mass fraction, %) of 0.40C-1.5Cr-3Ni-0.4Mo-0.2V (PCrNi3MoV) and0.25C-3Cr-3Mo-0.8Ni-0.1Nb (25Cr3Mo3NiNb), was investigated by using the smooth bar specimenssubjected to strained-controlled push-pull loading. It is found that both steels show cyclicsoftening, but 25Cr3Mo3NiNb steel has a lower tendency to cyclic softening. 25Cr3Mo3NiNb steel hashigher fatigue ductility, and its transition fatigue life is almost three times that of PCrNi3MoV.25Cr3Mo3NiNb steel also shows higher LCF life either at a given total strain amplitude above 0.5% orat any given plastic strain amplitude, despite its lower monotonic tensile strength than that ofPCrNi3MoV. It also means that 25Cr3Mo3NiNb steel can endure higher total strain amplitude andplastic strain amplitude at a given number of reversals to failure within 10~4. 25Cr3Mo3NiNb steelis expected to be a good gun steel with high LCF properties because only several thousand firingsare required for gun barrel in most cases.

Low cycle fatigue behavior of T4-treated Al-Zn-Mg-Cu alloys prepared by squeeze casting and gravity die casting

Gravity die casting(GC) and squeeze casting(SC) T4-treated Al-7.0Zn-2.5Mg-2.1Cu alloys were employed to investigate the microstructures,mechanical properties and low cycle fatigue(LCF) behavior.The results show that mechanical properties of SC specimens are significantly better than those of GC specimens due to less cast defects and smaller secondary dendrite arm spacing(SDAS).Excellent fatigue properties are obtained for the SC alloy compared with the GC alloy.GC and SC alloys both exhibit cyclic stabilization at low total strain amplitudes(less than 0.4%) and cyclic hardening at higher total strain amplitudes.The degree of cyclic hardening of SC samples is greater than that of GC samples.Fatigue cracks of GC samples dominantly initiate from shrinkage porosities and are easy to propagate along them,while the crack initiation sites for SC samples are slip bands,eutectic phases and inclusions at or near the free surface.

Effect of nano-sized Al2O3 reinforcing particles on uniaxial and high cycle fatigue behaviors of hot-forged AZ31B magnesium alloy

The effect of hot-forging process was investigated on microstructural and mechanical properties of AZ31 B alloy and AZ31 B/1.5 vol.%Al2 O3 nanocomposite under static and cycling loading. The as-cast alloy and composite were firstly subjected to a homogenization heat treatment at 450 ℃ and then an open-die forging at 450 ℃. The results indicated that the presence of reinforcing particles led to grain refinement and improvement of dynamic recrystallization. The forging process was more effective to eliminate the porosity in the cast alloy workpiece. Microhardness of the forged composite was increased by up to 80% and 16%, in comparison with those of the cast and forged alloy samples, respectively. Ultimate tensile strength and maximum tensile strain of the composite were improved by up to 45% and 23%, compared with those of the forged alloy in similar regions. These enhancements were respectively 50% and 37% in the compression test. The composite exhibited a fatigue life improvement in the region with low applied strain;however, a degradation was observed in the high applied strain region. Unlike AZ31 B samples, tensile, compressive and high cycle fatigue behaviors of the composite showed less sensitivity to the applied strain, which can be attributed to the amount of porosity in the samples before and after the hot-forging.

EFFECT OF MICROSTRUCTURE OF ALUMINIDE COATING ON HIGH-CYCLE FATIGUE PERFORMANCE OF COATING-SUPERALLOY SYSTEM

The high-cycle fatigue performance of different microstructures of aluminide coating- superalloy system has been studied at 900℃.The single phase coating of coarse equiaxial grain NiAI(β)has unfavorable eJfect onJatigue life of the coating-superalloy.The fatigue life may shorten if the coating of NiAl(β)was an enrichment of coarse refractory metal grains. While an improvement can be made by dispersing numerous secondary phase particles such as extreme.fine γ′,quasi-σ-phase and others.

Fatigue crack propagation in fine-grained magnesium under low temperature tension-tension cyclic loading

Fine-grained magnesium was tested under stress-controlled tension-tension cyclic loading at -30 ℃ and the tested sample was observed using scanning electron microscope and electron backscatter diffraction to explore the fatigue behavior and crack propagation. The fatigue data showed that the material experienced cyclic softening followed by cyclic hardening before the final fracture failure. The microscopic observations demonstrated that the cracks were almost perpendicular to the loading direction with some zigzags and the cracks progressed along both small angle grain boundaries and large angle grain boundaries. Although the cracks were mainly propagated along large angle grain boundaries, the value of grain boundary angle was not the primary factor to determine the crack propagation direction. The local residual strain from the rolling process was released due to the crack propagation and there was more strain relaxation at regions closer to the cracks.

Low cycle fatigue estimation of low yield point steel

With the development of technology for earthquake resistant,the research of the low yield point(LYP) steel which used for the fabrication of energy dissipation damper were paid more and more attention.The common studies of the low yield point steel is mainly about the performance with constant amplitude and constant frequency.The low cycle fatigue properties of low yield piont steel were studied by series of test with continuous varying amplitude and varying frequency with the materials testing system by us.The test results showed that low yield point steel of Baosteel have excellent low cycle fatigue properties,which meet the requirement for steel used for the fabrication of energy dissipation damper completely.The low cycle fatigue performance of low yield point steel of Baosteel mainly depended on the amplitude in test.And the effect of varying frequency for the low yield point steel was more less than varying amplitude.

Effects of Composition and Thermal Cycle on Transformation Behaviors,Thermal Stability and Mechanical Properties of CuAlAg Alloy

The phase transformation behavior, mechanical properties, and the thermal stability of CuAlAg alloy were studied and minor rare earth (0.1 wt pct La+Ce) was added to improve the mechanical property of the studied alloy. It was found that Ag addition in the CuAl binary alloy can improve the stability of martensitic transformation and high Al content leads to the disappearing of martensitic transformation. The tensile strength and strain of the Cu-10.6AI-5.8Ag (wt pct) alloy were measured to be 383.5 MPa and 0.86%, respectively. With rare earth addition, the tensile strain increased from 0.86% to 1.47%. The CuAlAg alloy did not exhibit martensitic transformation on the second heating process. Its poor thermal stability still needs to be improved.

Microstructure and Electrical Properties of Er_2O_3-Doped ZnO-Based Varistor Ceramics Prepared by High-Energy Ball Milling

The microstructure, electrical properties and density of ZnO-based varistor ceramics with different Er2O3 content prepared by high-energy ball milling （HEBM） and sintered at 800℃ were investigated. With increasing Er2O3 content, the ZnO grain size decreases due to the Er-rich phases inhibiting grain growth ; and nonlinear coefficient （ α ） decreases because of the decrease of barrier height （φB） The breakdown voltage （Eb） and density increase, whereas leakage current （IL） decreases with increasing Er2O3 content. The barrier height （φB）, donor concentration （Nd）, density of interface states （Ns） decrease and barrier width （ω） increases with increasing Er2O3 content due to acceptor effect of Er2O3 in varistor ceramics.

Microstructure and electrical properties of Y_2O_3-doped ZnO-based varistor ceramics prepared by high-energy ball milling

Y2O3-doped ZnO-based varistor ceramics were prepared using high-energy ball milling （HEBM） and low-temperature sin- tering technique, with voltage-gradient of 1934-2197 V/mm, non-linear coefficients of 20.8-21.8, leakage currents of 0.59-1.04 μA, and densities of 5.46-5.57 g/cm3. With increasing Y2O3 content, the voltage-gradient increases because of the decrease of ZnO grain size; the non-linear coefficient and the leakage current improve but the density decreases because of more porosity; the donor con- centration and density of interface states decrease, whereas the barrier height and width increase because of the acceptor effect of Y2O3 in varistor ceramics.

Influence of texture and microstructure on mechanical properties of high-strength wrought magnesium alloy AZ80

Monotonic (tensile and compressive) and high cycle fatigue properties of the forged magnesium alloy AZ80 were investigated by using specimens with load axis parallel to longitude (L) or transverse (T) direction. A pronounced directional anisotropy in monotonic tests was observed in AZ80, i.e. the yield stress in T-direction is significantly lower than that in L direction. However, the directional anisotropy is absent in fatigue, fatigue strengths in both L- and T-directions are essentially equal. The absence of directional anisotropy in fatigue is possibly associated with the microstructure of AZ80. A homogeneous single phase structure probably alleviates the directional anisotropy of fatigue properties of the wrought magnesium alloy.

Study on the Effect of Fibers on the Properties of Asphalt Mastics

To study the influence of fiber on the properties of asphalt mortar,the properties of lignin fiber,polyester fiber,and basalt fiber were summarized and analyzed respectively.The high-and low-temperature properties of fiber asphalt mortar were studied and analyzed by using three indexes,rutting factor and tensile fracture energy.The results showed that all three kinds of fibers could improve the performance of asphalt mortar to varying degrees,with lignin fiber demonstrating the best effect,followed by basalt fiber and polyester fiber.The type the fiber can be selected based on the required thermal stability and cost depending on the project type.

A damage-coupled multi-axial time-dependent low cycle fatigue failure model for SS304 stainless steel at high temperature

Based on the time-dependent strain cyclic characteristics and fatigue behaviors of SS304 stainless steel under multi-axial cyclic loading at 700 ？ C, and in the frame of unified visoco-plastic cyclic constitutive model and continuum damage mechanics theory, the damage-coupled multi-axial time-dependent constitutive model and fatigue failure model were proposed. In the model, the evolution equation of damage was introduced in and the time-dependent effects, e.g. holding time, loading rate, were taken into account. The model was applied to the simulation of whole-life cyclic deformation behaviors and prediction of LCF life for SS304 stainless steel in multiaxial time-dependent low cycle fatigue tests. It is shown that the simulated results agree well with experimental ones.