Reciprocating impact wear testing apparatus

A reciprocating impact wear testing apparatus has been developed for studies of wear occurring between solid materials undergoing repetitive impulsive loading. Such loading may be purely normal or may include simultaneous transverse sliding. The apparatus is designed to allow measurement of the impact load pulse and to provide for the maintenance of repeatable force pulses for the duration of a prolonged series of impacts (millions of cycles). When utilized with a flat-nosed impacting specimen, the time-invariant impulse waveform results in repeatable surface and subsurface stress cycling of materials undergoing wear. This paper describes the testing apparatus and procedures and includes results from a preliminary series of tests on two polymeric materials.     

微纳米力学测试系统的研制

采用闭环控制微纳压电位移驱动器为核心加载装置,以压电式微力传感器作为测量装置,集成显微光学数字视频监测系统,并编写完整的测量、控制与标定算法软件,研制量程0.1m N-500m N的全自动微纳米力学测试系统。该系统具有被测样品与实验探针的自动定位、可编程自动加载与显微实时监测与记录功能,能够满足小至微米级样品的实验要求,填补现有微纳测试仪器因量程过小或功能不足等问题所导致的空白,预期可应用于微纳机电、微纳米材料、生物医学工程等领域。     

Material transport phenomena in the impact wear of titanium alloys

Results are presented from compound impact wear studies performed with titanium alloys of different β phase content and morphology. The “material pair” consisted of a 17-4 PH stainless steel counterface and a flatended titanium alloy specimen. Each material pair was exposed to variations in relative transverse sliding velocity and number of repetitive load cycles. Testing was conducted primarily at a single level of nominal peak normal impulsive stress.Both optical and scanning electron microscopy were used to monitor changes in worn surface and subsurface regions. Energy-dispersive X-ray studies of the initial and worn surfaces comprising the material pair clearly indicated the nature of the material transport between the opposing surfaces. Wear debris were studied by optical microscopy and by powder X-ray techniques.Utilizing the reciprocating impact wear testing apparatus, it was determined that material transport appears to be a controlling factor. The type of transport (i.e. material passing from specimen to counterface or vice versa) was found to vary under differing test conditions. Such findings may contribute to the understanding of wear for systems other than those characterized by repetitive impulsive contact.Material removal is minimal at particular levels of relative transverse sliding velocity, and these levels are not necessarily affected by the magnitude of the nominal level of stress. It appears that the nature and quantity of the constituents (α, β) in the titanium alloys are critical in establishing wear behavior for the material pairs investigated.     

一种旋转式液固两相流冲蚀磨损试验装置的研制

针对目前液固两相流冲蚀磨损试验装置存在实际冲角误差大、浆体浓度不均匀等问题,研制了一种旋转式冲蚀磨损试验装置。该装置允许的冲角范围为0°~90°,冲击速度为0~28.5m/s连续可调,利用搅拌叶片和导流槽实现不同冲击速度下浆体浓度的均匀性,具有速度稳定、可同时测试8个不同冲角下的试样、操作方便等特点。对低碳钢在不同冲击速度和冲角下的试验表明,所测得试验数据误差在6.8%以内,冲蚀磨损规律与经典结论一致。因此,该装置有望作为一种准确可靠的冲蚀磨损试验研究新平台而应用于耐冲蚀磨损优化设计和寿命预测等领域。     

Three-body impact wear study on conventional and new P/M + HIPed wear resistant materials

A new hammer-mill type impact wear testing facility was built for impact wear testing and characterization. Tests with the hammer-mill impact wear device were carried out on conventional wear resistant materials such as Mn-steels of different compositions, white cast iron, and on new P/M+HIPed wear resistant materials. To verify the validity in using this laboratory wear testing apparatus, wear behavior and worn surfaces obtained on conventional and new Mn-steels generated from this device were compared with wear phenomena and worn surfaces developed in industrial applications, i.e. from certain types of rock crushers. The strain hardening effect in different Mn-steel grades was studied first. Second, the wear resistance of materials with different properties was studied using two different grades of abrasive. With silica sand (high hardness, low compressive strength), conventional Mn-steel and white cast iron perform in a manner comparable with the P/M+HIPed materials. With volcanite sand (low hardness, very high compressive strength), the P/M+HIPed wear resistant materials appear to have the best wear resistance.     

基于AMESim的衡器载荷测量仪泵控系统仿真研究

根据衡器载荷测量仪液压系统数学模型和PID控制系统模型,在AMESim中建立高精度载荷测量仪泵控系统的仿真模型。应用该模型对系统加载过程、恒载荷控制、响应时间、液压控制分辨率等特性进行了仿真分析,并依据仿真结果进行了管径选择,验证了系统设计的合理性。     

Evolution of Wear in a Two-Dimensional Bushing

A model for the evolution of wear for the shaft and bushing for a simple two-dimensional bushing system was developed under the assumptions of uniform contact pressure and constant applied load. A simple laboratory apparatus was constructed to test the model. Two experiments were run; one showed wear on the shaft only and the other showed wear on the bushing only. The results showed the predicted linear progression of wear.     

生物肢体皮肤冲击磨损舒适度试验机研制

假肢与肢体间的接触损伤是冲击和磨损共同作用导致的，而目前的皮肤磨损测试机不能模拟肢体与皮肤的真实摩擦情况。为此，研制一种生物肢体皮肤冲击磨损舒适度试验机。该试验机由肢体固定装置、挤压磨损装置、冲击嵌套磨损装置和支撑平台组成，能用于模拟假肢与肢体之间在挤压磨损以及冲击-嵌套磨损时摩擦磨损的运动状态，从而对皮肤与假肢接触产生的复杂应力条件下的磨损情况进行研究，为假肢的设计以及磨损情况分析提供依据。     

Development of an Apparatus to Investigate Friction Characteristics of Constant-Velocity Joints

Constant-velocity (CV) joints have become standard design and an integral part of modern vehicles, primarily due to their superiority in terms of CV torque transfer. Despite widespread usage of constant velocity joints there are certain aspects of their friction, wear, and contact characteristics that are not well understood. In this article, the need to directly measure CV joint internal contact and friction forces is addressed by designing and constructing an instrumented advanced CV joint friction apparatus using actual tripod-type joint assemblies. The apparatus is capable of measuring key performance parameters such as friction and wear under different realistic operating conditions of oscillatory speeds and CV joint articulation angles. The apparatus incorporates a custom-installed triaxial force sensor inside of the CV joint to measure in situ internal CV joint forces (including friction). The CV joint apparatus is under full computer control and is communicating with all measurement components via a master Labview control program. Experiments under different articulation angles and lubrication conditions were performed and the measurements were correlated with published data.     

Notes on contributors

Various metallic pairs were tested under conditions of unlubricated solid contact. Experiments were conducted for repetitive impulsive and continuous sliding contact. Wide ranges of materials and conditions (nominal contact stress and relative transverse sliding velocity) and a variety of loading modes (pure normal impact at various frequencies, compound impact at various sliding velocities, and pure sliding under various stress levels) were explored.Particular attention was focused on the establishment of subsurface material zones developed in the tests, in situ. These zones exhibit dependences on velocity, stress, material, test duration and loading mode. The experimental findings, based on several analysis techniques, serve to characterize subsurface zone composition and morphology. Both surface and subsurface features were examined by optical and electron microscopy and analyzed by energy-dispersive X-ray techniques to allow interpretations concerning the role of external parameters, material transport and debris formation, as well as insight into operative mechanisms which act on specific materials under prescribed conditions to cause wear.     

Transfer of semicrystalline polymers sliding against a smooth steel surface

The interrelationships between transfer and wear in polymers were studied using a pin-disk-type wear testing apparatus. The wear rates of polymers except polytetrafluoroethylene (PTFE) were high for up to about the first 100 revolutions of the disk and decreased gradually until the steady low wear rates which generally occurred after about 2000 revolutions. However, PTFE exhibited an almost constant high wear rate throughout the wear process. The thickness of transferred polymer increased rapidly with increasing number of revolutions in the initial wear stage but after about several hundred revolutions remained constant. A coherent transfer film was formed in most parts of the friction track after about 100 revolutions. It was found that polymer wear could occur in polymers sliding on a transferred polymer layer. All polymers except PTFE exhibited smaller wear rates when sliding on the transferred layer. The load dependence of the thickness was very small compared with that of the wear rate. PTFE produced a very dense and coherent transferred layer compared with that of other polymers. However, there was no clear relationship between friction and the thickness of the transferred polymer layer.     

Friction and wear behavior of three-dimensional braided carbon fiber/epoxy composites under dry sliding conditions

Sliding friction and wear characteristics of three-dimensional (3-D) braided carbon fabric reinforced epoxy resin (C_3D/EP) composites were investigated. Tests were performed on a MM200 tester under normal loads of 50, 150, and 250 N and velocities of 0.42 and 0.84 m/s. A quenched medium carbon steel with a hardness of HRC 52 was used as the counterpart material. The specific wear rate and the coefficient of friction were examined as a function of testing conditions (load, velocity, and sliding distance) and material parameters (fiber volume fraction and fiber–matrix bonding). The results showed that the coefficient of friction and the specific wear rate changed considerably during the running-in period and reached stable values at the steady wear stage. Fiber volume fraction and testing conditions (load and velocity) affected the wear more significantly than the friction. It was also found that fiber–matrix bonding had an impact on the friction and wear of the 3-D composites. Furthermore, the specific wear rate decreased with the increase in the product of load and velocity. Worn surfaces and debris were observed by scanning electron microscope (SEM) and wear mechanisms were discussed in this study.     

干摩擦状态下动载荷特性对磨损的影响

在自行研制的环一块磨损试验装置上研究了干摩擦状态下矩形波载荷特性对磨损的影响,结果表明。1)矩形波载荷和静载荷作用下试件的磨损过程一样,存在跑合期和稳定磨损期;2)矩形波载荷的占空比愈小,跑合期磨损量愈少,跑合期愈长。     

Effect of contact pressure on wear and friction of ultra-high molecular weight polyethylene in multidirectional sliding

Computational wear models need input data from valid tribological tests. For the wear model of a total hip prosthesis, the contact pressure dependence of wear and friction of ultra-high molecular weight polyethylene (UHMWPE) against polished CoCr in diluted calf serum lubricant was studied, and useful input data produced. Two test devices were designed and built: a heavy load circularly translating pin-on-disc (HL-CTPOD) wear test device and an HL-CTPOD friction measurement device. Both can be used with a wide range of loads. The wear surface diameter of the test pin was kept constant at 9 mm, whereas the load was varied so that the nominal contact pressure ranged from 0.1 to 20 MPa. The wear factor decreased with increasing contact pressure, whereas the coefficient of friction first increased with increasing contact pressure with low pressure values and then decreased. Up to the pressure of 2.0 MPa, the wear mechanisms and wear factors were in good agreement with clinical findings. In the critical range of 2.0-3.5 MPa, the wear mechanisms and wear factors started to differ from clinical ones, and the decrease of the wear factor steepened. The discrepancy became more and more evident as the pressure was gradually increased beyond 3.5 MPa. It appears that the pressure value of 2.0 MPa should not be exceeded in pin-on-disc wear tests that are to reproduce the clinical wear of UHMWPE acetabular cups.     

Wear of cardiac lead outer insulation due to internal cable motion

Insulation wear in implanted cardiac leads may result in serious failure modes, including inappropriate or missing therapy. A novel test apparatus intended to simulate a range of loading conditions between cardiac lead components has been developed. Wear testing performed in an aqueous environment at loads and velocities anticipated to occur in-vivo shows that a material with decreased toughness exhibited increased wear rate. Order of magnitude variability within test groups was observed, suggesting that reliability projections should incorporate the statistical nature of the wear rate. Ranking of implantable material wear rates are possible using this methodology.     

Loosening Evaluation of Bolted Joints Modified by Fine Particle Bombardment under Transverse Cyclic Loading

ABSTRACT

The objective of this article is to evaluate the loosening behavior of bolted joints modified by fine particle bombardment (FPB) under transverse cyclic loading. FPB treatment was conducted to thread surfaces of both the bolt and the nut. Self-loosening experiments were then performed on the bolted joint with high, medium, and low preload using a fatigue testing machine. The test results show that fretting wear occurs at the thread surface under transverse cyclic loading, which leads to gradual self-loosening of bolted joints without the rotation of the nut. FPB treatment alleviates thread wear by increasing the surface hardness and reducing the friction coefficient between threads, thereby improving the anti-loosening ability of bolted joints. After FPB treatment, the bolted joints with a lower preload exhibited a greater relative improvement in anti-loosening ability than those at a higher preload.     

全数字仪器化冲击试验机测控系统设计

设计了一种全数字仪器化冲击试验机测控系统,该系统为摆锤冲击试验机专用,可以与多种不同吨位的摆锤冲击试验机配套使用。该测控系统采用先进的虚拟仪器技术设计,测试与控制相结合,功能齐全,数据测试准确,操作界面美观大方,操作方便,通过普通计算机即可运行,主要功能包括冲击摆动作控制、数据采集、曲线显示、数据存储和处理、状态提示、试验报告打印等。     

A Device for Measuring the Complex Dielectric Constant of Liquid Dielectrics

A device for measuring the dielectric constant of liquid dielectrics using the waveguide method is described. Processing of the measurement results is based on the evaluation of the input impedance of the load, which is a segment of a waveguide line with a dielectric rod. It is proposed that measurements of the load reflection coefficient be performed at two frequencies, which allows the device to dispense with a measuring line. A technique for measuring and processing results is described. The measured dielectric constants of distilled water and cement mortar in the frequency range of 2.3–2.6 GHz are presented.     

The investigation of the steady stage of steel fretting

The effects of slip length, frequency, surface pressure and shape of the longitudinal oscillatory motion on the fretting wear of steel were investigated by a specially designed fretting apparatus using an M.T.S. closed loop axial hydraulic testing system.

The rate of fretting wear in the steady stage was found to increase with increasing slip length and specific surface pressure and to decrease with increasing cyclic frequency and material hardness. The wave shape of the oscillatory motion does not appear to affect the wear rate.

Increased slip, greater surface pressure and lower cycling frequency all promote the adhesion mechanism of fretting. With higher frequencies decreased slip and low surface pressures, the product of fretting wear is mainly oxides and oxidation is the leading wear mechanism.     

Impact wear of MgO single crystals I. Wear characteristics

The impact wear characteristics of MgO single crystals have been investigated using an impact testing machine provided with a sintered alumina hammer having a tip radius of 2 mm. There is a fixed zero wear duration time for each selected impact load. Plastic deformation caused by slip of the {110} planes and cracking by impact occur during zero wear, but wear fragment are not produced. The zero wear period corresponds to a process of impact fatigue. Measurable wear, which is obtained by repeated impact over the zero wear limit, depends on the impact load and the action of wear fragments. When the test is performed in water wear is accelerated by abrasive erosion caused by impulsive flow of water containing wear fragments between the hammer and the scar wall.