FEFG''''94 International Symposium on Fracture and Strength of Solids

Organized by the State Key Laboratory of Mechanical Structural Strength and Vibration, Chinese Society of Solid Mechanics of CSTAM. Sponsored by National Natural Science Foundalion of China. Objectives The objectives of the symposium are to foster research in the mechanics and phenomena of fracture, fatigue. and strength of materials, and also to promote cooperation among scientists and engineers in these fields.     

Design and application of refrigerant recovery and filling control system based on MSP430

提出了一种应用于空调系统的多功能冷媒回收加注装置的控制方案。本方案硬件电路基于MSP430单片机设计,同时采用了高精度称重传感器和高性能放大器;软件设计采用中位值平均滤波算法。本装置不仅可以将冷媒废液净化后回收,而且可以定量加注新冷媒。同时,本装置具有施压、抽真空、加冷冻油等功能。实践证明,本控制系统成本较低、稳定性好,具有较高的实用价值。     

Experimental studies on optimization of process parameters and finite element analysis of temperature and stress distribution on joining of Al�CAl and Al�CAl2O3 using ultrasonic welding

This study is carried out to optimize the process parameters like weld time, weld pressure, and amplitude of vibration to maximize the weld strength in Al?CAl welding using Taguchi??s design of experiments methodology. Experiments are conducted using 0.3-mm thick pieces of aluminum, and the temperature generated at the weld interface and the weld strength for all the specimens are measured. Also, a finite element model is developed that is capable of predicting the interface temperature and stress distribution during welding. Further, a preliminary study on the joining of alumina to aluminum is also carried out, and the finite element models of temperature and stress distribution during welding are simulated. Results of experimental work and FEM studies are compared and found to be in good agreement.     

Effect of γ irradiation on the scintillation and optical properties of lead tungstate crystals

The radiation hardness of a test batch of lead tungstate crystals grown by a new technology at the Bogoroditsk Technochemical Plant for the PANDA experiment has been measured. The optical properties of the crystals have been investigated at temperatures ranging from +20 to ?20°C under irradiation with a ¹³⁷Cs radionuclide source. The light yield in the crystal is seen to considerably increase with a decrease in its temperature. In addition, the loss of the crystal transparency under irradiation at low temperatures is higher than under irradiation at room temperature. As a result, at a fixed dose rate, the signal from the crystal at a negative temperature may be considerably greater than the signal at room temperature even if the accumulated dose is high.     

Review on Wind-Induced Stability and Vibration Effect of Large Cooling Towers

With the rapid development of China''s economy， the construction number of cooling tower in thermal/nuclear power plants in China keeps a rapid increase and the cooling tower structure tends to be ultra-high and super-large. The wind-induced shell stability and vibration effect have become key factors in the structural design and construction of cooling towers. A series of research progresses on wind-induced stability and wind-induced vibration effect of cooling towers are reviewed in this paper from the four aspects， including theoretical analysis， experimental simulation， numerical calculation and field measurement. It is demonstrated that the shell stability checking formulas based on uniformly-distributed circumferential wind loads are not suitable for the shell stability investigations of large cooling towers under the complex wind pressures. The necessity to establish the simulation criterion of dynamic flow at ultra-high Reynolds number adopted in the physical wind tunnel test based on the field measurements is emphasized. The field measurement of structural damping ratio values of cooling towers during the wind-induced dynamic analysis is suggested. In the future， it is urgent to carry out the studies on the shell instability performance and the mechanism of structural wind-induced effects under the actions of non-synoptic winds such as strong typhoons and tornadoes to meet the increasing design and construction demands of large cooling towers.     

Effect of the cut-off frequency on rough-point and flat-surface contacts?

In the past years, contact between two bodies has been studied from various ways that do not consider the cut-off frequency effect on the contact mechanism. This paper reports the correlation between rough point contact and flat surface contact at different cut-off frequencies of filter. The similarity and difference between the two types of contact mechanisms are presented for materials with linear or elasticperfectly plastic deformation. The conjugate gradient method (CGM) is used for analysing the rough point contact, while the rough flat surface contact is studied with an improved CGM in which the influence coefficient for the elastic deformation of the rough flat surface is obtained with finite element method. Numerical results show that for the above two types of contacts, their von Mises stress and maximum shear stress are greatly affected by the cut-off frequency of a high-pass filter. Moreover, a decrease in the cut-off frequency leads to an increase in the contact area and a decrease in the approach for the rough flat surface contact, while the opposite variations is for the point contact between rough bodies with the small radii.     

Effects of cold working and heat treatment on microstructure and wear behaviour of Cu–Be alloy C17200

The effects of cold work process between aging and solution heat treatment on the microstructure, hardness and the tribologic behaviour of a copper–beryllium (Cu–Be) alloy C17200 were investigated. The wear behaviour of the alloys was studied using ‘pin on disc’ method under dry conditions. The results show that the formation of fine grained structure and γ phase particles enhances the mechanical properties of the alloy; nonetheless, they do not reduce the wear rate. This is attributed to the capability of the softer specimens to maintain oxygen rich compounds during the dry sliding test.     

Influence of Thermal Treatment on Microstructure and Hardness of Niobium Alloyed PM‐Tool Steel

Abstract

This work describes carbides present in the tool steel containing 2.5% C, 3.3% Si, 6.2% Cr, 2.2% Mo, 2.6% V, 2.6% Nb, 1.0% W, prepared by the powder metallurgy (PM) process. The influence of thermal treatment conditions on carbide behavior is investigated. During austenitization, some dissolution of M₇C₃ occurs, while MC carbides are thermally stable. So, the quenched steel is composed of two types of carbides: chromium rich M₇C₃ and niobium rich MC, besides martensite and retained austenite. During tempering of the hardened steel at the temperatures above 480°C, the precipitation of very fine carbides and martensite recovery occur, which results in secondary hardening. Precipitated particles are predominantly vanadium and molybdenum rich MC, M₂C, and M₆C carbides.     

Effects of Chromium Addition on Microstructure and Abrasion Resistance of Fe–B Cast Alloy

This research work studies the effects of chromium on microstructure and abrasion resistance of Fe–B cast alloy. The results show that eutectic boride changes from continuous network to less continuous and matrix changes from pearlite to martensite with the increase in chromium content in the alloy. Meanwhile, an increase in chromium addition in the alloy leads to an increase in the chromium content in M₂B-type boride because chromium can enter boride by substituting for iron in Fe₂B. Under two-body wear, Fe–B cast alloy exhibits excellent wear resistance. When alloys are tested against soft abrasive, chromium can markedly improve the wear resistance of Fe–B cast alloy, whereas excessive chromium can reduce the wear resistance. The wear resistance of Fe–B cast alloy increases first and then decreases with the increase in chromium. But when tested against hard abrasive, since the hardness of SiC is much higher than that of M₂B boride, an increase in chromium content marginally increases the wear resistance. Weight losses of Fe–B cast alloy increase with the increase in the load and exhibit the linear relationship.     

Effect of Sliding Speed on Surface Modification and Tribological Behavior of Copper–Graphite Composite

In practice, the sliding speed is an important parameter for materials applied in sliding condition. We have conducted an experimental study to explore the effect of sliding speed on friction and wear performance of a copper–graphite composite. The sliding tests were carried out over a wide range of speeds with a pin-on-disc configuration. The results show that there is a critical speed at which there is a transition of the friction and wear regimes of the composite. In addition, the formation of a lubricant layer on the contact surface (surface modification) determines the actual tribological performance of the composite. The wear mechanisms in different wear regimes are also discussed.     

Design and experiment of ϕ-type-knots knotters on Chinese small square balers

Since the knotters on the Chinese rectangular balers are imported from outside of the country, Chinese knotters with independent intellectual property rights is far away from being closed. In order to harvest a large quantity of straw in a short period on the small-scale lands of China, basic requirements on the knotters are summarized. Mathematical model of the knotter is also determined uniquely. Furthermore, the ~-type-knots knotter equipped on the Chinese square baler to form the ~ type knots is designed. Knotting rate experiments of the qb-type-knots knotter on the test bench and in the wheat/maize straws covered fields are carried out to check the knotting performances of the knotter. The parameters of the formed knots are also tested. The experiments results show that the knotting rate of the qb-type-knots knotter reaches 100.0% on the test bench without straws, while reaches 99.6% in the wheat straws covered field and 100.0% in the maize straws covered field. The average maximum force in the knotting process is 194.7 N in the lab experiment. The length out of the knots formed in lab is 15.9%-20.6% lower than the knots formed in the field experiment. The breaking force of the knots formed in the field is 115.9%-167.2% higher than the knots formed in lab due to the higher preload and interactions with the compacted bales. Highly relevant relationships exist between the breaking force of the formed knots and the maximum force in the forming process of the knots in the lab experiment. The designed knotter breaks out the embarrassing situation of the domestic knotters which don＇t have independent intellectual property rights, and promotes the development of Chinese knotter technology, and the mathematical model is helpful for designing new type of knotters.     

Effects of electromagnetic stirring and rare earth compounds on the microstructure and mechanical properties of hypereutectic Al–Si alloys

In this paper, the effects of rare earth addition and electromagnetic stirring on the microstructure and the mechanical properties of hypereutectic Al–Si alloys have been reported. Hypereutectic Al–Si alloy was prepared using liquid metallurgy route and modified with the addition of cerium oxide. To control the structure, slurry of hypereutectic Al–Si alloy was subjected to electromagnetic stirring before pouring into the mould. It was observed that the addition of cerium oxide (0.2 wt.%) refined the primary silicon particles and modified the eutectic silicon particles. Further, the electromagnetic stirring of the hypereutectic Al–Si alloy reduced the average size of primary silicon particles, from 152?±?9 to 120?±?6 μm, and the length of β-intermetallic compounds decreased from 314?±?12 to 234?±?10 μm. Similarly, the application of electromagnetic stirring on cerium oxide-modified hypereutectic Al–Si alloy also reduced the average size of primary silicon particles from 98?±?5 to 76?±?4 μm and the average length of β-intermetallic compounds from 225?±?7 to 203?±?5 μm. Mechanical properties namely tensile strength, ductility and hardness of the alloys were improved with electromagnetic stirring and addition of cerium oxide appreciably.     

Effect of Titanium and Nitrogen Additions on the Microstructures and Three-Body Abrasive Wear Behaviors of Fe–B Cast Alloys

This study investigates the effect of titanium and nitrogen elements on the microstructures and wear behaviors of medium carbon Fe–B cast alloy. The as-cast microstructures of Fe–B cast alloy consist of the eutectic boride, pearlite, and ferrite. Moreover, the as-cast eutectic boride structures are greatly refined when titanium and nitrogen are added. The boride area fraction, average boride area, Rockwell hardness, etc., are also investigated systemically. The wear behaviors of medium carbon Fe–B cast alloy are studied by a three-body abrasive wear tester. The results show that the wear weight loss of Fe–B cast alloy with titanium and nitrogen elements is lower than that of the ordinary Fe–B cast alloy. Meanwhile, the wear mechanism of Fe–B cast alloy with different titanium and nitrogen concentrations is described and analyzed.     

Comparison of myocontrol and force control based on fitts’ law model

In recent years, many types of input modalities have been developed and used for a great variety of new devices and machines. To enhance the performance of the human-machine systems, well-designed human-machine interface (HMI’s) between the user and the machine are essential. Biosignal-based HMI’s have been appearing as an alternative to physical HMI’s that have been conventionally used. As a type of biosignal control, the electromyography (EMG) has been investigated as an input modality for prostheses, computers, and robotic exoskeletons. In this study, myocontrol is analyzed through direct and numerical comparison with force control. Mycontrol and force control of visual pointing tasks were tested with EMG and force signals provided as visual feedback, and the controllability of each control mode was evaluated based on Fitts’ law paradigm, which is a general estimation method of speed and accuracy of various movements. The experimental results show that both myocontrol and force control can be modeled using Fitts’ law, even when different types of signals were provided as visual feedback. Among the control modes, myocontrol and force control showed high controllability when force signal was used as visual feedback.     

Notes on “Single-machine scheduling with past-sequence-dependent setup times and effects of deterioration and learning”

The aim of this paper is to show by a counterexample that theorem 6 and corollary 5 in Wang et al. (Int J Adv Manuf Technol 41:1221–1226, 2009) are incorrect.     

Effect of strain amplitude and temperature on creep-fatigue behaviors of 9–12 % Cr steel

The creep-fatigue behaviors of P92 steel under strain range of 0.3 %–0.5 % and test temperature of 600–650 °C was studied carefully in this paper. With the increase of temperature, the creep-fatigue life is significantly reduced, and more vulnerable to temperature than strain amplitude. In addition, the dislocation density decreases with increasing creep fatigue, and the martensite laths become coarser. Furthermore, the increase of strain amplitude leads to more significant secondary cracks and fatigue striation. The higher temperature causes much deeper and larger dimples. During the test, the growth and accumulation of precipitates inevitably lead to stress concentration, resulting in material fracture and destruction. Finally, the linear cumulative damage (LCD), the modified ductility exhaustion (MDE) and the frequency separation life (FSL) model are used to predict the creep-fatigue life of P92 steel, and it is found that the frequency separation life model had the highest prediction accuracy among the threes.

     

Investigations on influence of process variables on crater dimensions in micro-EDM of γ-titanium aluminide alloy in dry and oil dielectric media

In micro-electro-discharge machining (EDM), challenge lies in enhancing material removal rate while retaining precision in crater dimensions. Material properties of both anode and cathode and the process variables have significant control on MRR and accuracy. In the present research, experiments were conducted on γ-titanium aluminide alloy work piece using 200-μm steel electrode. The circular craters were produced both in the presence and absence of dielectric fluid using varying micro-EDM process variables, i.e., open-circuit voltage, discharge capacitance, pulse frequency, and pulse-on time. Overcut was measured from optical microscope images using Image Analyzer software. Influences of process variables and optimal conditions for minimum overcut on crater dimensions were investigated using ANOVA test, which shows that capacitance of RC circuit contributes significantly in crater formation followed by pulse frequency. Regression equations of overcut for both dielectric mediums were developed using discharge energy and spark-on time as two functions. It was also investigated that overcut was less in air medium compared to oil medium.     

Effect of silicon content on wear resistance and corrosion behaviour of Al–Si eutectic alloy

Abstract

In the present study, Al–Si eutectic alloys produced at the Aluminium Institution were studied. The alloys were cast and forged into bars of 20 mm diameter. The results obtained were compared with a pure aluminium sample. Metallographic analysis, spectral analysis, SEM and energy dispersive spectroscopy analysis, pin on disk abrasive wear tests and mass loss tests were performed. Wear resistances of alloys with various silicon contents were tested under different loads and constant abrasive speed. SiC abrasive paper of 80 grit size was used. The dry sliding tests were carried out under loads of 10, 20 and 30 N and the testing was conducted under a constant sliding velocity of 36˙8 m min^–1 in a dry air atmosphere. Corrosion rates were determined in 0˙1M NaCl acid solutions. The corrosion tests were performed at 2, 4, 6 and 8 h. The wear and corrosion resistance of all the eutectic alloys increased with increasing silicon content in the matrix.     

Fabrication,characterization and evaluation of the effect of PLGA and PLGA–PEG biomaterials on the proliferation and neurogenesis potential of human neural SH-SY5Y cells

In recent years with regard to the development of nanotechnology and neural stem cell discovery, the combinatorial therapeutic strategies of neural progenitor cells and appropriate biomaterials have raised the hope for brain regeneration following neurological disorders. This study aimed to explore the proliferation and neurogenic effect of PLGA and PLGA–PEG nanofibers on human SH-SY5Y cells in in vitro condition. Nanofibers of PLGA and PLGA–PEG biomaterials were synthesized and fabricated using electrospinning method. Physicochemical features were examined using HNMR, FT-IR, and water contact angle assays. Ultrastructural morphology, the orientation of nanofibers, cell distribution and attachment were visualized by SEM imaging. Cell survival and proliferation rate were measured. Differentiation capacity was monitored by immunofluorescence staining of Map-2. HNMR, FT-IR assays confirmed the integration of PEG to PLGA backbone. Water contact angel assay showed increasing surface hydrophilicity in PLGA–PEG biomaterial compared to the PLGA substrate. SEM analysis revealed the reduction of PLGA–PEG nanofibers' diameter compared to the PLGA group. Cell attachment was observed in both groups while PLGA–PEG had a superior effect in the promotion of survival rate compared to other groups (p < .05). Compared to the PLGA group, PLGA–PEG increased the number of Ki67⁺ cells (p < .01). PLGA–PEG biomaterial induced neural maturation by increasing protein Map-2 compared to the PLGA scaffold in a three-dimensional culture system. According to our data, structural modification of PLGA with PEG could enhance orientated differentiation and the dynamic growth of neural cells.     

Effect of Bio-Lubricant and Biodiesel-Contaminated Lubricant on Tribological Behavior of Cylinder Liner–Piston Ring Combination

This article addresses the issue of friction and wear characteristics of diesel engine cylinder liner–piston ring combinations under different lubricating conditions using a pin-on-disc wear tribometer. The discs were made out of actual engine cylinder liner material using a casting process. Pins were made out of top compression ring material. The tests were conducted on a pin-on-disc tribometer for wear and friction characteristics of the cylinder liner and piston ring combination with diesel-contaminated rapeseed oil–based bio-lubricant, diesel-contaminated commercial synthetic lubrication oil (SAE 20W40), biodiesel-contaminated commercial synthetic lubrication oil (SAE 20W40), and used (150 h) commercial synthetic lubrication oil (SAE 20W40). Experimental results demonstrated that the rapeseed oil–based bio-lubricant and biodiesel-contaminated synthetic lubricant exhibited better performance in terms of wear, friction, and frictional force under similar operating conditions. Thus, usage of newly formulated bio-lubricant and biodiesel in the long run may have a positive impact on engine life.