环模材料抗植物磨料磨损激光淬火工艺参数优化

为了探索提高环模材料抗植物磨料磨损的表面强化工艺,对环模常用材料45#钢进行激光淬火处理,通过磨料磨损试验,利用正交试验设计,探讨了不同激光淬火工艺参数对材料耐磨性的影响。试验数据分析显示:3个工艺参数对磨损量影响大小顺序为激光功率、扫描速度和光斑直径,耐磨性的最优参数组合为激光功率2050W、扫描速度20mm/s、光斑直径4mm。植物磨料对未经激光淬火的45#钢的磨损机制主要为显微切削+粘着磨损,激光淬火后的45#钢磨损机制主要为机械抛光+显微切削,且其表面犁削深度较之未经激光淬火处理的试件明显浅而窄。

环模材料4Cr13磨料磨损试验及其表面强化

自制磨料磨损试验机对环模材料4Cr13试样进行磨损试验,利用单因素试验和正交试验探究了橡胶轮转速、压力以及磨料粒径对4Cr13试样磨损量的影响规律和影响程度。采用等离子喷焊技术在4Cr13试样表面喷涂铁基(Fe65)耐磨涂层,并对耐磨涂层进行性能测试。结果表明:磨损量随着压力的增加而增加,当压力进一步增加到100 N时,磨损量增速变快;橡胶轮转速对磨损量的影响为先增加后减少,当转速增加到120 r/min时磨损量开始减少;磨料粒径的变大导致了磨损量的增加;3个因素对磨损量影响的主次顺序为压力、磨料粒径、橡胶轮转速;在橡胶轮转速为100 r/min,压力为80 N,粒径为2.5 mm的条件下进行磨损试验,测得喷有耐磨涂层4Cr13试样的磨损量为15.3 mg,4Cr13试样的磨损量为40.8 mg,耐磨涂层体现出良好的耐磨性。

雷氏夹环模材料及其弹性介绍

根据不同材料制成的雷氏夹环模弹性不同，导出了雷氏夹环模弹性变形的计算公式，指出影响环模弹性变形的因素是环模轴线半径、环模厚度和高度，并指出在弹性极限内，环模弹性大小不影响试验结果。，取Ｅ＝１．１５×１０５ＭＰａ，当在两指针根部加挂３００ｇ质量砝码时，计算的两指针根部的垂直位移量为：而实际测量两指针根部的垂直位移量为。２，７０ｍｍ。计算值未考虑指针圆弧段的影响，因此，计算值小于实测值。３雷氏夹环模弹性的影响因素从上式可以看出，影响雷氏夹环模弹性的因素有作用在指针根部的载荷、环模轴线半径、环模厚度和高度以及材料的种类。不同材料的弹性模量不同。弹性模量越大，环模越不容易变形，因而弹性越小。相同条件下，黄铜制成的雷氏夹，其环模的弹性变形量约是不锈钢质材料的２倍。同一种材料的环模，变形量分别与环模轴线半径的三次方和载荷成正比，而与环模厚度的三次方和高度成反比。可见，如果环模平均厚度较小或环模半径较大时，将使环模弹性迅速增大。经计算，一般情况下，当其它条件不变，环模厚度比标准要求小０．０５ｍｍ时，两指针尖端距离增加就要大于２０ｍｍ＊。特别是铜质材料的耐磨性很差，使用时装填浆体和取出试件都不可避免地要使环模内表面产生磨损?

40Cr热喷涂件抗植物磨料磨损性能试验

在苜蓿草颗粒制粒过程中,苜蓿草粉对金属材料的磨损是导致环模失效的主要原因。为了探索提高环模材料抗植物磨料磨损的表面强化工艺,利用火焰喷涂技术对40Cr钢进行表面强化处理,通过磨料磨损试验,探讨了不同重熔时间对材料耐磨性的影响,利用XRD分析了涂层的相结构,应用扫描电镜观察分析了涂层磨损表面形貌和磨损机理。结果表明,重熔时间是影响火焰喷涂涂层性能的重要因素,当40Cr基体的Ni60A自熔性合金涂层的厚度为1mm,保温时间为8h时,10min为较合理的重熔时间。热喷涂工艺提高了40Cr材料的抗苜蓿草粉的显微切削能力,形成的犁沟浅,表面颗粒在循环载荷的作用下产生犁削现象,并伴有表面裂纹。颗粒周边的裂纹在循环应力的剪切作用下萌生扩展,最终呈层状剥落。

Numerical method and model for calculating thermal storage time for an annular tube with phase change material

For calculating the thermal storage time for an annular tube with phase change material （PCM）, a novel method is proposed. The method is suitable for either low-temperature PCM or high-temperature PCM whose initial temperature is near the melting point. The deviation fit is smaller than 8% when the time is below 2x104 s. Comparison between the predictions and the reported experimental data of thermal storage time at same conditions is investigated and good agreements have been got. Based on this method, the performance of the thermal storage unit and the role of natural convection are also investigated. Results show a linear relation between the maximum amount of stored heat and thermal storage time, and their ratio increases with the height of the thermal storage unit. As the thickness of the cavity increases, natural convection plays an increasingly important role in promoting the melting behavior of paraffin. When the thickness of the cavity is small, natural convection restrains the melting behavior of paraffin.

The Flexible Housing： Criteria and Strategies for Implementation of the Flexibility

The design of housing systems is today challenged by a highly uncertain context, dominated by the rapid development of functional and technological obsolescence in inherited housing models. If flexibility is the ability of a system to be easily modified and to respond to changes in the environment timely and conveniently, it can be considered as the antidote to obsolescence or the characteristic of the system that guarantees slippage over time. Our paper focuses on the concept of flexibility as a fundamental prerequisite for residential building in order to extend its life cycle design, through strategies and constructive solutions that ensure both the convertibility of the space in response to changing usage and the use of building materials that encourage the reversibility and the long-term easy maintenance of the technological choices that have been implemented. Flexibility is examined both from a conceptual point of view, so as to obtain a clear and logical definition that is distinct from related terms, as well as from a practical point of view, by finding ways to incorporate this requirement into the designing of housing.

Monitoring the Modal Frequency and Velocity Variations of Bridges under Ambient Excitation

We conducted a long-term monitoring experiment on the Lutuanxilu Bridge located in Changping District of Beijing, employing our recently developed real-time bridge monitoring system based on the Guralp CMG-6TD broadband seismometer. We identified the modal parameters with the stochastic subspace identification( SSI) algorithm,and continuously monitored the temporal velocity variation with coda wave interferometry.The results show that:( 1) the highly sensitive Guralp CMG-6TD broadband seismometer,which records the three-component vibration signal within broad frequency range,is well suited for long-term bridge health monitoring.( 2) With the continuous vibration signal from ambient excitation,the stochastic subspace algorithm can robustly identify the low-order modal parameters and the coda wave interferometry can accurately monitor the tiny velocity variation.( 3) The elastic modulus of bridge materials changes significantly associated with varying temperature,leading to diurnal velocity variation with amplitude of approximately 1%. The velocity variation shows strong negative correlation with temperature fluctuation. Meanwhile,the modal frequencies remain quite stable,suggesting that the velocity variation may be a more sensitive quantitative damage index.( 4) While the modal frequencies reflect the integrated health status of the bridge,the velocity variation can be utilized to monitor the local elastic modulus. Therefore,it is crucial for bridge health monitoring to continuously monitor the two key damage indexes under ambient excitation.

Material Parameters of a Structural Steel with Plastic Strain Memory

The present work is concerned with the characterization of hardening parameters for an elasto-plastic continuum model, taking into account the memory effect of plastic strain amplitude, in order to predict the hysteretic responses of a ferritic steel. This elasto-plastic three-dimensional model is based on the internal thermodynamic variables which composed of the nonlinear kinematic hardening and isotropic hardening with the plastic strain memorization. The emphasis is put on the determination of strain memory parameters along with other material parameters of the proposed model in order to better simulate the behavior of the material at different strain range. The material parameters are calibrated with the experimental stabilized loops of stress-strain curves available in the literature. The predicted stabilized loops from the simulation with the determined parameters show good agreement with the experimental results signifying the validity of the considered model.

Analytical investigations and fuzzy logic-based modeling of the impact resistance of aluminum-epoxy laminated composites

In the present paper, Charpy impact resistance of aluminum-epoxy laminated composites in both crack divider and crack ar-rester configurations has been investigated. In both configurations, an analytical investigation has been carried out to evaluate the effects of layers thickness on impact resistance of the specimens. A model based on fuzzy logic for predicting impact re-sistance of the specimens has been presented. For purpose of building the model, training and testing using experimental re-sults from 126 specimens produced from two basic composites were conducted. The data used for the input data in fuzzy logic models are arranged in a format of 7 input parameters that cover the thickness of layers, the number of layers, the adhesive type, the crack tip configuration, the content of SiC particles, the content of methacrylated butadiene-styrene particles and the number of test trial. According to these input parameters, in the fuzzy logic model, the impact resistance of each specimen was predicted. The training and testing results in the fuzzy logic model have shown a strong potential for predicting impact resis-tance of aluminum-epoxy laminated composites.