高弹沥青混合料疲劳性能试验研究

高弹沥青混合料在公路工程中有着广泛应用,其疲劳性会对性能及使用效果造成影响。基于此,先对高弹沥青疲劳性能进行了分析,然后在此基础上,通过试验的方式,对其疲劳性能进行深入研究,希望文中内容对相关工作人员的工作能够有所帮助。

儿童推车手把强度疲劳性测试方法的研究与实现

对儿童推车手把强度疲劳性试验方法进行了研究,并据此研制了儿童推车手把强度疲劳性试验机,实现了对各类儿童推车手把进行800次或3000次疲劳性试验。采用PLC控制,以触摸屏(Touch Panel Computer)作为人机界面,控制工作气缸按预先设置的方式对儿童推车手把进行疲劳试验,并对儿童推车故障状态进行监控。

国产激光照排(影像)片的定影速度试验报告

本文摘要报告用两种不同牌号的国产定影液(广州科艺牌和南阳华光牌)对不同厂家生产的激光照排胶片(上海、保定、二胶)进行定影速度和定影液疲劳性试验的对比性试验结果。

重载车制动鼓标准对比及金相组织差异探讨

比较国内外重载汽车制动鼓的标准,总结了制动鼓失效机理。各标准中关于制动鼓金相组织中碳化物加磷共晶数量有差异,如一厂商制动鼓中碳化物加磷共晶数量比其他标准高很多,力学性能不但不差却较其他标准要高,机械加工性无差别,而且这在多年的市场应用中得到了实际检验。这与一般的认知相左,故而提出问题,进行探讨。

Low cyclic fatigue performance of concrete-filled steel tube columns

Eight concrete-filled steel tubular(CFT) columns were tested subjected to cyclic loading under constant axial load. Experimental parameters included axial compression ratio, loading sequences, and strength of concrete and steel. The seismic performance of CFT columns and failure modes were analyzed. The test results show that different axial load ratios and loading sequences have effects on the load carrying capacity, ductility and energy dissipation capacity of CFT columns, as well as the failure modes of the CFT columns. The failure pattern can be categorized into two types: local buckling failure of steel tube in compression zone, and low cycle fatigue tearing rupture failure of steel tube. The seismic behavior was evaluated through the energy index obtained from each cycle.

Metal magnetic memory field characterization at early fatigue damage based on modified Jiles-Atherton model

In order to propel the development of metal magnetic memory （MMM） technique in fatigue damage detection, the Jiles-Atherton model （J-A model） was modified to describe MMM mechanism in elastic stress stage. A series of rotating bending fatigue experiments were conducted to study the stress-magnetization relationship and verify the correctness of modified J-A model. In MMM detection, the magnetization of material irreversibly approaches to the local equilibrium state Mo instead of global equilibrium state M^n under cyclic stress, and the M0-a curves are loops around the Mar,-a curve. The modified J-A model is constructed by replacing M~ in J-A model with M0, and it can describe the magnetomechanical effect well at low external magnetic field. In the rotating bending fatigue experiments, the MMM field distribution in normal direction around cylinder specimen is similar to the stress distribution, and the calculation result of model coincides with experiment result after some necessary modifications. The MMM field variation with time at a certain point in fatigue process is divided into three stages with the variation of stable stress-stain hysteresis loop, and the calculation results of model can explain not only the three stages of MMM field changes, but also the different change laws when the applied magnetic field and initial magnetic field are different. The MMM field distribution in normal direction along specimen axis reflects stress concentration effect at artificial defect, and the magnetic signal fluctuates around the defect at late fatigue stage. The calculation results coincide with the initial MMM principle and can explain signal fluctuates around the defect. The modified J-A model can explain experiment results well, and it is fit for MMM field characterization.

Long term performance of warm mix asphalt versus hot mix asphalt

The fatigue behavior, indirect tensile strength （ITS） and resilient modulus test results for warm mix asphalt （WMA） as well as hot mix asphalt （HMA） at different ageing levels were evaluated. Laboratory-prepared samples were aged artificially in the oven to simulate short-term and long term ageing in accordance with AASHTO R30 and then compared with unaged specimens. Beam fatigue testing was performed using beam specimens at 25 ℃ based on AASHTO T321 standard. Fatigue life, bending stiffness and dissipated energy for both unaged and aged mixtures were calculated using four-point beam fatigue test results. Three-point bending tests were performed using semi-circular bend （SCB） specimens at -10 ℃ and the critical mode I stress intensity factor K1 was then calculated using the peak load obtained from the load-displacement curve. It is observed that Sasobit and Rheofalt warm mix asphalt additives have a significant effect on indirect tensile strength, resilient modulus, fatigue behavior and stress intensity factor of aged and unaged mixtures.

Evaluation of environmental factors to fatigue performance of asphalt mixes

This paper studies the effect of different environmental factors, including the axle load weight, environmental temperature, vehicle speed, and the aging level of asphalt, on the fatigue performance of asphalt mixes based on four-point bending beam fatigue tests. A fractional factorial design method named ＂uniform design＂ was applied in experimental design. The relations of the environmental factors to initial stiffness, fatigue life, phase angle and cumulative dissipated energy were established with the general linear modeling method. It is found that there exists very good correlativity between the environmental factors and the fatigue performance indices of asphalt mixes. The coefficients of total correlation are mainly beyond 0. 95. The results indicate that the consideration of the effect of environmental factors is necessary in the fatigue performance evaluation on real asphalt pavement.

Acoustic Emission Properties of Concrete Slab During Fatigue Testing with a Running-Wheel Load

AE （acoustic emission） signals from concrete slab during fatigue testing with a running-wheel load were evaluated. The signals were recorded by remote sensors connected to a computer network. The sensing equipment consisted of 60 kHz resonant-type AE sensors mounted on a reinforcing steel bar as a waveguide, together with a 16-channel sensor highway AE system. Because the detected AE signals included periodic mechanical noise from the motion of the wheel, these noises were eliminated by means of signal processing. The AE waveguide measurement over a length of 3 m detected fractures as vertical and horizontal cracks in the RC （reinforced concrete） slab. Those cracks were analyzed by correlating AE parameters with macroscopic distortions and the numbers of fatigue cycles. In the AE events and AE energy, two types of AE phenomena, active region and inactive region, were observed during fatigue testing. The vertical cracks were characterized by an AE amplitude of 58 dB, a peak frequency of 30 kHz, and a ratio of the rise time to the maximum amplitude value （RA） of 100. The horizontal cracks were characterized by an AE amplitude of 85 dB, a peak frequency of 60 kHz, and an RA value of 10.

High Cycle Fatigue Life Prediction and Reliability Analysis of Aeroengine Blades

Based on the nonlinear continuum damage model （CDM） developed by Chaboehe, a modified model for high cycle fatigue of TC4 alloy was proposed. Unsymmetrical cycle fatigue tests were conducted on rod specimens at room temperature. Then the material parameters needed in the CDM were obtained by the fatigue tests, and the stress distribution of the specimen was calculated by FE method. Compared with the linear damage model （LDM）, the dam- age results and the life prediction of the CDM show a better agreement with the test and they are more precise than the LDM. By applying the CDM developed in this study to the life prediction of aeroengine blades, it is concluded that the root is the most dangerous region of the whole blade and the shortest life is 58 211 cycles. Finally, the Cox propor- tional hazard model of survival analysis was applied to the analysis of the fatigue reliability. The Cox model takes the covariates into consideration, which include diameter, weight, mean stress and tensile strength. The result shows that the mean stress is the only factor that accelerates the fracture process.