Excellent mechanical properties and resistance to cavitation erosion for an ultra-low carbon Cr Mn N stainless steel through quenching and partitioning treatment

The retained austenite content(RAC),the mechanical properties,and the resistance to cavitation erosion(CE)of the00Cr13Mn8Mo N steel after quenching and partitioning(Q&P)processing were investigated.The results show that the Q&P process affected the RAC,which reached the maximum value after partitioning at 400°C for 10 min.The tensile strength of the steel slightly decreased with increasing partitioning temperature and time.However,the elongation and product of strength and elongation first increased and then decreased.The sample partitioned at 400°C for 10 min exhibited the optimal property:a strength-ductility of 23.8 GPa?%.The resistance to CE for the 00Cr13Mn8Mo N steel treated by the Q&P process was improved due to work hardening,spalling,and cavitation-induced martensitic transformation of the retained austenite.

Mathematical modeling for dynamic stability of sandwich beam with variable mechanical properties of core

The paper is devoted to mathematical modelling of static and dynamic stability of a simply supported three-layered beam with a metal foam core. Mechanical properties of the core vary along the vertical direction. The field of displacements is for- mulated using the classical broken line hypothesis and the proposed nonlinear hypothesis that generalizes the classical one. Using both hypotheses, the strains are determined as well as the stresses of each layer. The kinetic energy, the elastic strain energy, and the work of load are also determined. The system of equations of motion is derived using Hamilton＇s principle. Finally, the system of three equations is reduced to one equation of motion, in particular, the Mathieu equation. The Bubnov-Galerkin method is used to solve the system of equations of motion, and the Runge-Kutta method is used to solve the second-order differential equation. Numerical calculations are done for the chosen family of beams. The critical loads, unstable regions, angular frequencies of the beam, and the static and dynamic equilibrium paths are calculated analytically and verified numerically. The results of this study are presented in the forms of figures and tables.

Enhanced cavitation erosion resistance of a friction stir processed high entropy alloy

Friction stir processing of an Al0.1CoCrFeNi high entropy alloy(HEA)was performed at controlled cooling conditions(ambient and liquid submerged).Microstructural and mechanical characterization of the processed and as-cast HEAs was evaluated using electron backscatter diffraction,micro-hardness testing and nanoindentation.HEA under the submerged cooling condition showed elongated grains(10μm)with fine equiaxed grains(2μm)along the boundary compared to the coarser grain(~2 mm)of as-cast HEA.The hardness showed remarkable improvements with four(submerged cooling condition)and three(ambient cooling condition)times that of as-cast HEA(HV^150).The enhanced hardness is attributed to the significant grain refinement in the processed HEAs.Cavitation erosion behavior was observed for samples using an ultrasonication method.All of the HEAs showed better cavitation erosion resistance than the stainless steel 316L.The sample processed under a submerged liquid condition showed approximately 20 and 2 times greater erosion resistance than stainless steel 316L and ascast HEA,respectively.The enhanced erosion resistances of the processed HEAs correlate to their increased hardness,resistance to plasticity,and better yield strength than the as-cast HEA.The surface of the tested samples showed nucleation and pit growth,and plastic deformation of the material followed by fatigue-controlled disintegration as the primary material removal mechanism.

Mathematical Modeling of Heat Flux Distribution in Raw Cotton Stored in Bunt

The scientific article examines the physical and mechanical properties of raw cotton stored in buntings in cotton palaces. Because during the storage of raw cotton in bunts, some of its properties deteriorate, some improvements. Therefore, the mathematical modeling of storage conditions of raw cotton in bunts and the physical and mechanical conditions that occur in it is of great importance. In the developed mathematical model, the main factor influencing the physical and mechanical properties of raw cotton is the change in temperature. Due to the temperature, kinetic and biological processes accumulated in the raw cotton in Bunt, it can spread over a large surface, first in a small-local state, over time with a nonlinear law. As a result, small changes in temperature lead to a qualitative change in physical properties. In determining the law of temperature distribution in the raw cotton in Bunt, Laplace’s differential equation of heat transfer was used. The differential equation of heat transfer in Laplace’s law was replaced by a system of ordinary differential equations by approximation. Conditions are solved in MAPLE-17 program by numerical method. As a result, graphs of temperature changes over time in raw cotton were obtained. In addition, the table shows the changes in density, pressure and mass of cotton, the height of the bun. As the density of the cotton raw material increases from the top layer of the bunt to the bottom layer, an increase in the temperature in it has been observed. This leads to overheating of the bottom layer of cotton and is the main reason for the deterioration of the quality of raw materials.

高温后不同降温方式对600MPa级高强钢筋力学性能的影响

本文研究了高温后不同降温方式对600MPa级高强钢筋表观形貌与力学性能的影响,分析了其应力-应变曲线、屈服强度、极限强度、断后伸长率以及最大力下总伸长率等力学响应的变化规律。试验结果表明:自然降温与炉内降温方式对高强钢筋力学性能的影响接近,而浸水降温方式对高强钢筋力学性能的影响较大,尤其是在经历800℃高温后,其各项力学性能变化显著。此外,本文还建立了高温后不同降温方式下600MPa高强钢筋的数学模型,能够较好地预测其力学性能。

MODELING OF FERRITE GRAIN GROWTH OF LOW CARBON STEELS DURING HOT ROLLING

For most commercial steels the prediction of the final properties depends on accurately calculating the room temperature ferrite grain size. A grain growth model is proposed for low carbon steels Q235B during hot rolling. By using this model, the initial ferrite grain size after continuous cooling and ferrite grain growing in coiling procedure can be predicted. In-plant trials were performed in the hot strip mill of Ansteel. The calculated final ferrite grain sizes are in good agreement with the experimental ones. It is helpful both for simulation of microstructure evolution and prediction of mechanical properties.

Effect of annealing treatment on microstructures,mechanical properties and cavitation erosion performance of high velocity oxy-fuel sprayed NiCoCrAlYTa coating

The mechanical parts serving in the marine environment are up against the dual damage of corrosion and cavitation erosion,so the Ni Co Cr Al YTa coating with excellent corrosion resistance is successfully prepared by high velocity oxy-fuel(HVOF)sprayed technology to protect the equipment from deterioration.The chemical composition and mechanical properties as well as the microstructure evolution of the coating before and after annealing treatment are studied.At the same time,the influence of annealing treatment on the corrosion and cavitation erosion behaviors of the coating is investigated,as well.The NiCoCrAlYTa coating mainly containsγ-Ni,β-Ni Al,andγ’-Ni3Al phases.During the deposition,the microcrystals or incomplete crystals generate in the interior of the coating because of the large temperature difference and impact force.Meanwhile,there is twin crystal structure in the as-spayed coating.After annealing treatment,the growth of grains and the segregation of reactive elements improve interface strength and inhibit the formation of micro-defects in the coating.The annealing temperature is of significance to the microstructure,mechanical properties,anti-corrosion and cavitation erosion resistance of the coating.This study provides a combined approach toward improving the corrosion and cavitation erosion resistance of NiCoCrAlYTa coatings.

Effects of simulated on-fire processing conditions on the microstructure and mechanical performance of Q345R steel

A series of simulated on-fire processing experiments on Q345R steel plates was conducted, and the plates＇ Brinell hardness, ten- sile strength, and impact energy were tested. Microstructure morphologies were systematically analyzed using a scanning electron micro- scope with the aim of investigating the effect of the steel＇s microstructure on its performance. All examined performance parameters exhib- ited a substantial decrease in the cases of samples heat-treated at temperatures near 700℃. However, although the banded structure decreased with increasing treatment temperature and holding time, it had little effect on the performance decline in fact. Further analysis revealed that pearlite degeneration near 700℃, which was induced by the interaction of both subcritical annealing and conventional spherical annealing, was the primary reason for the degradation behavior. Consequently, some nonlinear mathematical models of different mechanical perform- ances were established to facilitate processing adjustments.

Effect of inertial acoustic cavitation on antibiotic efficacy in biofilms

Bacterial biofilms can lead to chronic infections,increase tolerance to antibiotics and disinfectants,resistance to phagocytosis,and other components of the body’s immune system.Biofilm formation is implicated in the persistence of staphylococcal infections and chronic Pseudomonas aeruginosa lung infections in cystic fibrosis(CF)patients(which can result from biofilm-growing mucoid strains).Conventional treatments utilize aggressive antibiotic prophylaxis/therapy to prevent/eliminate biofilms,followed by chronic suppressive therapy.Recently,the use of enzymes to dissolve the biofilm matrix was investigated,in addition to quorum sensing inhibitors to increase biofilm susceptibility to antibiotics.Here,we propose a novel strategy,utilizing ultrasound-induced inertial cavitation,to increase antibiotic efficacy.The wall shear stress at the biofilm interface is calculated,and viscoplastic constitutive equations are used to examine the biofilm response to the mechanical stress.Our simulations suggest that the maximum biofilm detachment occurs at high pressure/low frequency,and the mechanical disruption can affect the biochemical processes inside the biofilm resulting in vulnerability to antibiotics.

基于数学模型的黄麻纤维材料化学改性试验研究

天然纤维增强塑料的主要缺点是增强纤维和基体之间的兼容性差。有必要使纤维与基体形成牢固的附着,以获得最佳性能。研究对黄麻纤维进行了化学处理,以改变纤维力学性能,建立数学模型提高纤维识别效率。分析了黄麻纤维的力学性能、表面形态和傅里叶变换红外光谱,以了解化学改性对纤维的影响。结果表明:化学改性可以有效提高纤维力学性能,且所建立的模型可以提高纤维识别效率,经过处理的纤维具有更好的界面附着力。黄麻纤维的化学处理对黄麻纤维复合材料的力学性能及微观结构有很大影响。

天然海水浸泡对FRP筋抗压性能的影响

针对天然海水浸泡条件下玻璃纤维增强复合材料(GFRP)筋、玄武岩纤维增强复合材料(BFRP)筋,开展了60℃恒温水浴加速老化试验以及抗压性能试验研究。基于试验结果,分析了不同浸泡时间对不同直径GFRP筋和BFRP筋受压破坏模式和抗压性能的影响。基于Weibull模型量化了GFRP筋和BFRP筋60℃恒温海水水浴后抗压强度的变异性。结果表明,60℃恒温海水侵蚀了FRP的表观面貌,90 d的抗压强度与弹性模量相对于0 d分别下降了13.06%和6.41%。在相同浸泡时间内,直径16 mm的FRP筋弹性模量比直径25 mm高4.17%,且直径相同的BFRP筋的弹性模量高于GFRP筋。Weibull模型量化了FRP筋试件抗压性能随海水浸泡时间变化的累积失效概率,准确捕捉抗压强度的变异性,为评估海水浸泡后FRP筋性能退化离散性提供了参考。

空气悬架用电磁直驱式空气压缩机设计与分析

针对传统空气悬架用空气压缩机结构复杂、体积较大的问题,提出了一种双气缸对置分布的电磁直驱式空气压缩机。首先建立了电磁直驱式空气压缩机的数学模型,然后对压缩机参数进行了灵敏度分析,并以直线执行器电磁效率和排气量作为优化目标,采用多目标遗传算法对选取的参数进行了优化。最后,与原系统中的旋转式空气压缩机进行了比较。结果表明:优化后排气量由22 L/min提升为25 L/min;相较于旋转式空气压缩机,电磁直驱式空气压缩机理论上体积和质量均减小,力学性能良好;充气工况下到达预定压力比旋转式压缩机快0.6 s,电磁效率提高21%。

聚醚型热塑性聚氨酯薄膜的真空干燥特性研究

采用模压成型工艺将聚醚型热塑性聚氨酯粒料压制成膜,研究了温度对TPU薄膜真空干燥特性的影响,计算了干燥过程中的有效扩散系数和扩散活化能,选取了5种干燥动力学模型进行拟合分析,并考察了不同温度干燥前后TPU薄膜力学性能的变化。结果表明:真空干燥温度越高,干燥速率越快,干燥时间越短,同时,TPU薄膜的干燥过程主要发生在降速阶段。两相扩散方程能够很好的反映TPU薄膜真空干燥过程中的水分比变化规律,计算得出其有效水分扩散系数为2.26×10^(-10)-7.28×10^(-10)m^(2)/s,扩散活化能为37.49 kJ/mol。此外,聚醚型TPU薄膜的断裂伸长率几乎不因吸水和干燥过程发生变化,而60℃以下的真空干燥可使其因吸水而降低的拉伸强度得到明显恢复。

空化热效应对上游泵送机械密封润滑性能的影响

机械密封端面空化现象是影响机械密封润滑性能的重要因素。采用计算流体动力学方法,基于Antoine公式,建立了考虑空化热效应的计算流体动力学模型,并与常用的仅考虑端面液膜粘温效应的模型进行对比,分析了空化热效应对密封性能的影响。结果表明:在低转速下,空化热效应的影响可以忽略,但在高转速下空化热效应使上游泵送机械密封的高压区形成能力减弱,泵送量降低,开启力降低;在高转速工作条件下分析密封失效机理时,除了考虑黏温效应之外,还要考虑空化热效应的影响;空化热效应使螺旋槽槽区局部温度比仅考虑黏温特性时稍高;考虑空化热效应时,动环端面空化发生程度最严重,由动环端面沿膜厚方向至静环槽底,空化区域越来越小,槽底空化区域最小,此规律与仅考虑黏温关系时相反。

空蚀与冲蚀交互作用下锡黄铜的材料流失及力学性能研究

利用转盘式磨损试验机模拟船用螺旋桨实际运行工况,通过失重分析、表面和截面形貌观察及力学性能测试,探讨了锡黄铜在含沙量不同的介质中空蚀与冲蚀交互作用下的材料流失规律及力学性能。结果表明:在含沙量为1kg/m3的测试介质中,空蚀与冲蚀交互作用下锡黄铜的材料流失孕育期很短,主要经历上升期、稳定期、衰减期,而当含沙量增加至2 kg/m3时,在相同交互作用时间内材料失重率明显增加,且稳定期不明显。空蚀与冲蚀交互作用后,锡黄铜表面呈现无明显方向性的短程犁沟状、鱼鳞状凹坑,存在明显的加工硬化现象。

钢的气蚀抗力与力学性能的相关性

本文在对四种材料多种热处理工艺条件下的气蚀模拟试验的基础上，提出了一个用钢的静拉伸和示波冲击试验所测试的机械性能而构成的复合力学参量评定其气蚀失重率的数学函数。并经实验证明，钢的气蚀抗力除取决于其自身的力学性能外，还应考虑钢的热稳定性及物理化学性能。

岩石损伤力学理论模型初探

分析了岩石全应力-应变曲线的特征、岩石在受载过程中同时引起弹性模量的降低和产生塑性应变的现象,提出了弹性模量、塑性应变与损伤成正比的基本假设和准静态损伤过程的概念,分析了损伤变量与损伤应变能释放率二者之间的依存关系,并定义了这两个概念。依据能量守恒定律,提出了岩石准静态损伤过程的数学模型,建立了无因次损伤演化和本构方程,并对其特点进行了分析,所建立的数学模型仅需3个材料常数,而且,可较为方便地确定。岩石全应力-应变曲线的峰前和峰后只用一个损伤演化方程,且与试验曲线能较好地吻合。

三维编织复合材料力学行为研究进展

对三维编织复合材料的细观结构几何模型和力学性能的研究进展进行了综述。重点介绍近几年该领域的研究成果和作者的一些研究工作,其中包括三维编织复合材料力学性能的实验研究和理论研究。在理论研究方面,介绍了弹性应变能法、纤维倾斜模型、三细胞模型和有限元模型等工作。最后,对未来的研究趋势进行了展望。

FLAC锚杆单元模型的修正及其应用

对FLAC2D3.3中的锚杆单元模型进行了修正,使其具备模拟锚杆损伤软化的功能。实例分析表明,修正后的模型可有效模拟大变形巷道锚杆支护的特有规律。

天然气水合物岩样三轴力学试验研究

天然气水合物是一种洁净、高效、资源量巨大的新型能源,而天然气水合物的力学性质与水合物的钻探、海底地质灾害等密切相关,因此,开发天然气水合物需要了解其力学性质。为此,用覆膜砂烧结成岩样,采用原位合成方式制取不同水合物饱和度的水合物沉积物岩样,利用自主研制的水合物原位测量系统,在不同围压条件下研究了不同水合物饱和度的水合物沉积物岩样的力学性质。结果表明,水合物沉积物岩样的抗压峰值强度随着围压、水合物饱和度的增大而增大,内聚力随着水合物饱和度的增大而增大,而泊松比、内摩擦角不随水合物饱和度变化。根据库伦-摩尔准则并结合试验结果建立了围压、水合物饱和度与含水合物岩样峰值强度的半经验数学模型,可为深水水合物钻探所涉及的水合物强度参数的选取,以及室内试验的理论分析及数值模拟提供一定的支持。