Copper-Free Resin-Based Braking Materials:A New Approach for Substituting Copper with Fly-Ash Cenospheres in Composites

Copper particles emitted from braking have become a significant source of environmental pollution.However,copper plays a crucial role in resin-based braking materials.Developing high-performance braking materials without copper has become a significant challenge.In this paper,the resin-based braking materials were filled with flyash cenospheres to develop copper-free braking materials.The effects of fly-ash cenospheres on the physical properties,mechanical and friction and wear properties of braking materials were studied.Furthermore,the wear mechanism of copper-free resin-based braking materials filled with fly-ash cenospheres was discussed.The results indicate that the inclusion of fly-ash cenospheres in the braking materials improved their thermal stability,hardness and impact strength,reduced their density,effectively increased the friction coefficient at medium and high temperatures,and enhanced the heat-fade resistance of the braking materials.The inclusion of fly-ash cenospheres contributed to the formation of surface friction film during the friction process of the braking materials,and facilitated the transition of form from abrasive wear to adhesive wear.At 100-350℃,the friction coefficient of the optimal formulation is in the range of 0.57-0.61,and the wear rate is in the range(0.29-0.65)×10^(-7) cm^(3)·N^(-1)·m^(-1),demonstrating excellent resistance to heat-fade and stability in friction coefficient.This research proposes the use of fly-ash cenospheres as a substitute for environmentally harmful and expensive copper in brake materials,which not only improves the performance of braking materials but also reduces their costs.

Study on frictional behavior of SiC_(f)/SiC composite clad tube clamping condition under nuclear irradiation

Silicon carbide fiber reinforced silicon carbide matrix(SiC_(f)/SiC)composite is the key cladding material of nuclear fuel,which determines the safety and reliability of nuclear fuel storage and transportation.The replacement of its storage and transportation scenario needs to be completed by the manipulator,but the application of SiC_(f)/SiC wear,fracture,and nuclear leakage in the snatching process of brittle-flexible-rigid contact in the irradiation environment has been seriously restricted due to unclear understanding of the damage mechanism.Therefore,the effects of irradiation dose and clamping load on the friction characteristics of the contact interface between SiC_(f)/SiC clad tube are studied in this paper,and the effects of irradiation parameters and clamping force on the static friction coefficient of the contact interface between the clad tube and flexible nitrile are obtained.Based on the Greenwood-Williamson tribological model,a numerical model of the shape and structure of the contact micro-convex at the micro-scale of the clamping interface is constructed by introducing the multi-surface integral,and finally verified by experiments.The research results show that there is a unique“Irradiation suppression zone”under the clamping condition of SiC_(f)/SiC cladding tube under the nuclear irradiation environment,and the growth of static friction coefficient slows down until stagnates after irradiation reaches a certain extent(600 kGy),and there will be a decline when the irradiation dose continues to increase,among which the clamping force of 15.2 N within the irradiation interval of 1,000 kGy can meet the safety of nuclear environment operation.The results of this paper can provide an important theoretical basis and application guidance for the safe operation of SiC_(f)/SiC cladding tubes in the storage and transportation clamping process.

Dry friction damping mechanism of flexible microporous metal rubber based on cell group energy dissipation mechanism

Flexible microporous metal rubber (FMP-MR) is a high-damping material that dissipates energy by dry friction through internal spiral metal wires in contact with each other. However, the FMP-MR energy dissipation mechanism is not fully understood owing to its disordered grid interpenetrating structure. In this work, computer-aided preparation technology is used to accurately reconstruct the complex spiral network structure of FMP-MR multipoint random contact, and a cell group model with an energy dissipation mechanism is proposed to obtain the dynamic energy distribution of the contact friction in both space and time dimensions. By judging the effective contact point, a global displacement ablation phenomenon of hooked staggered porous materials is induced. The macro- and micro-equivalent frictions are introduced to effectively explain the characteristics of the strong energy dissipation in FMP-MR under fretting excitation. A real and effective damping hysteresis constitutive model is then constructed to dynamically capture the mapping relationship between the complex nonlinear topological structure effect of the materials and spatial random contact dry friction in real time. The results indicate that the contact behavior between turns of the FMP-MR wire follows a clear quasi-Gaussian distribution under an external load, forcing the topological results to change. The energy dissipation of the materials revealed peak energy consumption lagging behind the loading limit for a certain distance, which can be determined by the effective contact point and contact dry friction slip. The consistency between the quasi-static compression tests and constitutive curves of the model was quantitatively verified through residual analysis. The data demonstrated the differential behavior of the FMP-MR meso-structure to follow a phased growth law during loading with different action mechanisms in the guiding, main growth, and relaxation stages of the energy consumption displacement curve. In summary, these findings provide an acceptable theoretical basis for the damping energy consumption mechanism and lifetime prediction of FMP-MR.

复合合金化对奥氏体中锰钢切削加工性的影响及切削加工性的模糊综合评判

在传统奥氏体中锰钢中添加不同含量的合金元素Mo, Cr, Nb和RE进行复合合金化处理,测试了其导热性及切削加工性,研究了复合合金化对奥氏体中锰钢切削加工性的影响,建立了二级模糊综合评判模型,以奥氏体锰钢的硬度、抗拉强度、延伸率、冲击韧性和热导率作为影响因素,对切削加工性进行定量分析.结果表明,复合合金化处理可一定程度上改善奥氏体锰钢的切削加工性,合金元素Mo, Cr和Nb含量分别为1.87wt%, 2.43wt%和0.059wt%时试样的刀具后刀面平均磨损宽度VB值比未经合金化处理的ZGMn13钢减少了14.3%.用二级模糊综合评判模型对奥氏体锰钢的切削加工性进行评价,通过本模型获得的评价指标与刀具磨损实验获得的VB值相关性显著,相关系数为–0.87334,存在高度的线性负相关,评判结果与VB值基本一致,评判模型符合生产实际,结果准确有效.

Potential Application of Entangled Porous Titanium Alloy Metal Rubber in Artificial Lumbar Disc Prostheses

Entangled Porous Titanium Alloy Metal Rubber(EPTA-MR)was used as a nucleus pulposus material in the design of non-fusion intervertebral disc prosthesis for the first time.A novel artificial lumbar intervertebral disc prosthesis was designed by reconstructing the lumbar model with reverse engineering technology,and the biomechanical behavior of the prosthesis was simulated under varied working conditions.The nucleus pulposus size was determined by the actual size of human prosthesis.EPTA-MR samples with different densities were prepared by medical titanium alloy wire experimental studies were conducted on static stiffness,damping energy consumption,and fatigue life.The results indicated that the static stiffness of EPTA-MR could reach approximately 1500 N mm and its loss factor remained higher than 0.2,and the variation range was relatively small,with excellent vibration damping capacity and bearing capacity.Among them,the overall performance of EPTA-MR with a density of 2.5 g em 3 was closer to that of the physiologic intervertebral disc.A macro experiment of five million fatigue vibration tests combined with microstructure observation exhibited a wear rate of only 0.9396 g-MC with no noticeable change in the internal micro-morphology.Therefore,the EPTA-MR has a broad application prospect as the nucleus pulposus material of artificial intervertebral disc prosthesis.