Damage model for environmental conditioned fatigue test with CAST

The aim of this paper is to suggest a unified test method that allows investigation into the different effects and contribution of water damage and temperature cycles on fatigue performance of asphalt mixtures by means of a CoAxial Shear Test (CAST). A continuum damage approach, based on the elasticity theory, is chosen to determine the damage level of each tested specimen. The proposed mathematical model allows the simulation of the modulus evolution in the fatigue test and takes into account the temperature cycles. In this way, a unique scalar damage factor determines the damage process severity in each specimen and allows a rational comparison between each different condition.     

Characterization of fatigue damage for paving asphaltic materials*

This study investigates the fatigue characteristics of typical bituminous materials used in road applications. Fatigue testing was performed in a four‐point bending beam test apparatus under controlled strain and stress conditions. Fatigue life was defined using the classical approach as the number of cycles, N_f, to 50% reduction in the initial stiffness modulus. It has also been defined in terms of macro‐crack initiation, N₁. A different approach, based on the linear reduction in stiffness during a particular stage of a fatigue test, was introduced to define a damage parameter, and the evolution of this damage parameter with number of cycles was used to characterize fatigue life. Furthermore, refinements to the linear damage model were introduced to take into account the difference in the evolution of dissipated energy between controlled strain and stress testing modes. These modifications have enabled the identification of a unique fatigue damage rate for both controlled strain and stress test modes.     

几种常用的金属材料疲劳极限试验方法

金属疲劳试验用于测定金属材料的许用疲劳应力,绘制材料的疲劳曲线,进而在交变应力下测定金属材料的疲劳极限。疲劳研究的试验方法有很多,该文根据有关国家标准和现有文献资料对一些常用疲劳试验方法进行了综述,包括单点疲劳试验法、升降法疲劳试验、高频振动疲劳试验法、超声波法疲劳试验、红外热像技术疲劳试验方法,并对每种疲劳试验方法的试验目的、适用条件、试验试样、所需仪器、具体步骤和数据处理进行了介绍。     

Forced modes of dilute binary gas mixtures

Anomalous forced sound dispersion in dilute binary gas mixtures is studied as a function of the mass ratio of the two components, using one- and two-temperature theories as well as different interparticle potentials. For a disparatemass mixture, such as He-Xe, the results are compared with previous work due to Johnson et al. It is suggested that even for nondisparate-mass mixtures, a one-temperature treatment is not appropriate.Paper presented at the Ninth Symposium on Thermophysical Properties, June 24–27, 1985, Boulder, Colorado, U.S.A.     

Application of a material fatigue damage model in 4PB tests

The fatigue property of an asphalt mix is an important issue in pavement design. This property is often determined with the aid of a four-point bending (4PB) test in controlled deflection mode. The fatigue property is related to the decrease in the calculated complex stiffness modulus, however, due to the non- homogenous stress and strain field in the beam, the measured response does not represent the stiffness modulus of the material but a weighted stiffness value. For a correct interpretation, a fatigue damage material model like the Asphalt Concrete Pavement-Fatigue model is needed. After integration, the calculated and measured responses are compared. By varying the model parameters, an excellent comparison between the two responses is obtained up to a certain number of cycles. This number of cycles is denoted as the fatigue life N _PH . The accumulated dissipated energy at the surface of the beam in the midsection can be expressed as a constant times the fatigue life N _PH to the power z and also as a constant times the product of the fatigue life N _PH and the initial dissipated energy in the first cycle. Using these two findings, a Wöhler curve was established similar to the one directly based on the strain amplitudes and fatigue life data.     

Analysis of the influence of binder properties on the mechanical response of bituminous mixtures

Asphalt mixtures are composed by a mass of aggregates (more than 90% of their total weight), which are bonded by a bituminous binder. Despite the fact that the binder is not the main component of these materials (around 5% of their total weight), it exerts a high influence on their mechanical response. In this sense, the service life of asphalt pavements will directly depend on the type of binder used, and thus an adequate choice is crucial to construct more durable roads. Because of this fact, it is necessary to know the characteristics of the bitumen in order to reduce the impact of different distresses that appear on roads. For this purpose, this paper studies the influence of the binder properties in the appearance of the main distresses that affect asphalt pavements around the world (stripping, fatigue cracking and plastic deformations). Five bitumens with different properties have been analysed during this research using diverse binder (UCL, multiple stress creep and recovery test and dynamic shear rheometer time sweep) and mixture (water sensitivity, wheel tracking and UGR-FACT) tests. The results obtained show that the properties of the binder influence the long-term performance of bituminous mixtures. In this sense, it can be said that flexible binders which are able to recover plastic deformations could extend the service life of the pavements.     

Estimation of the endurance fatigue limit for structural steel in load increasing tests at low temperature

The endurance fatigue strength of structural steel S355 was investigated in fatigue tests according to the method of increasing stress amplitude. The so‐called ‘load increasing test’ is based on the direct correlation between the fatigue limit and the temperature changes caused by local plastic deformation ahead of the tip of a micro crack, which was initiated as a result of cyclic loading. In the present work the fatigue limit for testing temperatures 40°C and ?20°C was estimated not only from the temperature measurements but also from the electrical potential measurements. Further, the obtained results were validated in standard fatigue tests with constant stress amplitude and a very good agreement was found.     

RCA粗骨料在沥青稳定碎石中掺量确定方法研究

为了解决RCA在沥青稳定碎石应用中存在的问题,本文引入振动成型法对不同RCA粗骨料掺量下的ATB-25进行体积参数、力学参数和路用性能的测试,建立了基于力学参数及路用性能的沥青稳定碎石中RCA粗骨料合理掺量范围的计算模型。研究结果表明,RCA粗骨料掺量的增加降低了ATB-25毛体积相对密度,对VV、VMA、VFA无明显影响,同时降低了MS、τ、Ri等力学参数值;RCA不利于ATB-25水稳定性及低温抗裂性,但对高温稳定性有利。RCA粗骨料在沥青稳定碎石中合理掺量范围计算模型RRCAC=[0,min(RRCAC1,RRCAC2)]%能够在保证力学参数及路用性能合格的前提下计算出RCA掺量上限。振动成型法提高了含RCA粗骨料沥青稳定碎石的室内成型标准,对提高RCA利用率及沥青稳定碎石路用性能效果显著。     

湿热环境下含分层平面编织玻璃纤维/环氧树脂基复合材料层合板振动特性

该文研究了玻璃纤维编织复合材料制成的可收卷层板在大变形条件下的弯曲静力性能和疲劳性能。通过弯曲静力试验得到了试验件在大变形条件下的应变和位移的关系;通过有限元模拟静力试验并与试验结果对照,确定了疲劳试验的载荷;研究了在大变形条件下不同铺层层板的弯曲疲劳寿命及失效模式和相同铺层层板的疲劳寿命曲线。结果表明：复合材料层板在大变形弯曲时具有明显的非线性行为,且(±45°)铺层层板弯曲疲劳性能明显优于(0°/90°)铺层层板;在最小应变和最大应变比不变的情况下,相同铺层层板的弯曲最大应变和对数疲劳寿命之间存在线性关系。     

Laboratory versus plant production: impact of material properties and performance for RAP and RAS mixtures

Agencies are moving towards performance-based design methodologies for asphalt pavements, and different methods to evaluate the asphalt performance in the laboratory have been developed. The laboratory performance can be evaluated at the mix design and/or production stages. A good understanding of differences in the behaviour of mixtures produced in the laboratory and plant is required to assess anticipated field performance at the mix design stage. The objectives of this paper are to compare the measured properties of plant-produced and laboratory-produced mixtures, to evaluate the effect of mixture variables on the differences observed, and to translate these to anticipated differences in fatigue performance through pavement evaluation using a linear viscoelastic layered analysis. In this study, 11 plant mixed, plant compacted, and their corresponding laboratory-mixed, laboratory-compacted mixtures are evaluated through binder and mixture testing. Mixture variables include aggregate gradation, binder grade and source, and recycled materials’ type and content. Performance grading on extracted and recovered binders, and complex modulus and SVECD fatigue testing on mixtures were conducted, and fatigue life was predicted using layered viscoelastic pavement design for critical distresses software. Most of the results show the laboratory mixtures are generally stiffer than the plant mixtures, but there is no constant shift for all mixtures. Larger differences are observed for the 19 mm and PG 58-28 mixtures and binder source appears to influence the differences as well. Different plants result in different effects on the properties of plant and lab-produced mixtures. This study provides a unique set of data that expands understanding of differences between laboratory and plant production of asphalt mixtures.     

基于热红外成像技术的300M钢疲劳极限测定

对经过热处理和未经过热处理的超高强度300M钢在室温下的常规疲劳性能进行了研究,用红外成像仪测量了疲劳试验过程中合金表面的温度变化;根据疲劳试验过程中温度-应力关系及试样表面温度分布差异,确定疲劳断裂位置和疲劳极限。结果表明:根据试件表面温度变化可以预测疲劳断裂位置;以此法确定的热处理300M钢疲劳极限为833MPa,与常规疲劳试验测得的疲劳极限吻合较好;加载初期300M钢升温到一定温度后形成平稳段,在断裂前温度快速升高。     

复合材料滚动轴承的疲劳试验研究

通过对复合材料滚动轴承的疲劳试验,研究了短纤维注射成型工艺研制的玻纤／尼龙６６滚动轴承的疲劳寿命和失效形式,为复合材料滚动轴承的设施应用有价值的参考。     

离心式静扭台加载扭矩分析

对离心式静扭台进行了动力学和运动学分析,建立了系统工作时的数学模型;探求了数学模型的理论解;运用计算机模拟计算了实验台工作过程中扭矩波形畸变规律,得出了扭矩波形畸变的实质是系统发生了二次谐波共振的结论;实验证明理论模型和理论求解方法的正确性。本理论模型和理论求解可为进一步分析实验台的振动性能及实验台主要参数的优化设计提供必要分析手段。     

二道次高温后Q345B钢的高周疲劳及γ-P-S-N曲线研究

为评估二次火灾后钢材的疲劳性能,以工程常用钢Q345B为研究对象,通过不同道次的升温、自然冷却模拟多次火灾环境,采用轴向拉伸与高周疲劳实验,对室温和经历二道次700、800℃高温自然冷却后的Q345B试样的拉伸与疲劳性能进行研究。结果表明：经过高温热处理的Q345B钢屈服平台更为明显;同一道次热处理温度越高,拉伸性能降低越明显。随着热处理温度的升高,组织中珠光体减少,显微组织趋于结构均匀化;在二道次高温自然冷却后Q345B钢微观组织中的珠光体基本消失,显微组织由铁素体组成。根据实验结果,建立二道次高温自然冷却后Q345B钢的中值S-N曲线模型,随着温度的增加,Q345B钢的疲劳强度及寿命下降明显;在同一道次下,不同温度的中值S-N曲线趋于平行。通过采用单侧容限系数法得到基于置信度和试件存活率的安全疲劳设计曲线,即概率γ-P-S-N曲线,利用该模型可对火灾后Q345B钢的疲劳性能进行有效评估。     

金属材料疲劳试验与数据处理方法

疲劳是金属材料机械构件常见的一种失效形式,疲劳试验方法与数据处理方法一直是研究学者们关注的热点。该文从疲劳寿命和规定寿命下的疲劳强度两个方面介绍了疲劳试验和数据处理方法的主要研究成果,并说明了几种典型的疲劳寿命试验方法与疲劳寿命概率分布参数的统计方法,以及规定寿命下的疲劳强度试验方法与规定寿命下的疲劳强度概率分布参数的统计方法;并通过算例,对比了不同方法之间的差异。