Optimal design of journal bearings

A new mathematical optimization technique, geometric programming, is used to optimize a number of journal bearing design problems. Though a few simplifying assumptions must be made in order to write the bearing design problem mathematically, no additional simplifying assumptions are required in order to apply geometric programming. Geometric programming is found to be a powerful technique for optimizing journal bearing design problems.     

Tribological failure analysis of journal bearings used in sugar mills

In present paper the premature failure of journal bearings encountered in sugar mills has been analyzed. The causes of bearing failure are identified by simulating the operating conditions and conducting controlled experiments on a fully automated Journal Bearing Test Rig with provisions for varied combination (i.e. load, speed, and lubricating oil) of operating conditions. The results of performance behavior (i.e. coefficient of friction, change in surface roughness and weight loss) of the bearings as observed in these experiments have been reported. The theoretical and experimental results indicate the existence of boundary lubrication conditions in sugar mill journal bearings. To mitigate the problem of relatively high wear, lubricating oil with boundary additives have been tried and results are reported.     

Nonlinear dynamic behavior and bifurcation analysis of a rigid rotor supported by a relatively short externally pressurized porous gas journal bearing system

Summary A numerical analysis of a rigid rotor supported by relatively short externally pressurized porous gas journal bearings is presented for nonlinear dynamic behavior and bifurcation. The compressible Reynolds' equation is solved by the finite differences method, and the successive over relaxation method and a time-dependent mathematical model for porous gas journal bearings are studied. A comparison of the results for the system state trajectory, Poincaré maps, power spectra, and bifurcation diagrams is made, and the dynamic behavior of the rotor center in the horizontal and vertical directions under different operating conditions is analyzed. The analysis shows the existence of a complex dynamic behavior comprising periodic and quasi-periodic response of the rotor center. This paper shows how the dynamic behavior of this type of system varies with changes in rotor mass and bearing number.     

Optimum design of aramid-phenolic/glass-phenolic composite journal bearings

Composite journal bearings are increasingly employed in large journal bearings for marine applications because composite materials can eliminate the seizure problem between the journal and the bearing during the start and stop periods of journals. Recently, aramid/glass reinforced phenolic composite journal bearings have been employed rather than the asbestos-phenolic composite bearings due to the health hazard of asbestos. In this work, the mechanical properties of aramid/glass reinforced phenolic composite were measured in order to analyze the stress on the journal bearing using the finite element (FE) method. The failure modes of the aramid/glass reinforced phenolic composite journal bearings were observed. The modified dimensions of aramid/glass reinforced phenolic composite journal bearings and the optimum interference fit amount were suggested using the FE-analysis results.     

Adhesive joining of composite journal bearings to back-up metals

Composite journal bearings are becoming popular for marine applications because they eliminate the possibility of seizure to steel journals, which is a drawback of white metal bearings. However, a reliable joining method for composite bearings to steel housings is required. In this work, hybrid composite journal bearings composed of carbon/phenolic and glass/epoxy laminated composites were manufactured with different stacking sequences and adhesively bonded to steel housings. The effect of deformations of the composite bearings due to thermal residual stresses on the adhesive joint performance was estimated with respect to stacking sequence by finite element method, and compared to the experimental results. From the measured and experimental results, it was found that the outward radial deformation of the composite bearings was beneficial to the adhesively bonded joint strength of the hybrid composite journal bearing.     

Surface roughness effects in dynamically loaded short bearings

Summary In this paper, the stochastic theory developed by Christensen is applied to the analysis of dynamically loaded short rough bearings. Approximate polynomial in place of Gaussian is used to represent the roughness height. To make the analysis applicable in real lubrication situations, it is assumed that the surface roughness and the minimum film thickness are of the same order. Attention is focussed on cyclic squeeze films under sinusoidal loading. It is concluded that the load is increased in the longitudinal case as compared with the transverse case. This happens due to excessive side leakage in the latter case. The effect of roughness is much more pronounced at the time when the load reverses its direction in both longitudinal and transverse cases.List of symbols c radial clearance - D diameter of the journal - e eccentricity - E() expectation of () - f(h _s ) probability density function - h film thickness - h _n nominal film thickness - h _s asperity height - H _n dimensionless nominal film thickness - L ₀ bearing length in the axial direction - n revolutions per unit time - p hydrodynamic pressure - P ₀ unit loading - R radius of journal - S Sommerfeld number - t time - T dimensionless time - U tangential velocity of the journal - V ₀ normal velocity of the journal centre - angular velocity of the journal - _L frequency of applied load - _p frequency of oscillation - W load capacity - W _a mean amplitude of the load - W ₀,W _/2 load components along and perpendicular to the line of centres - eccentricity ratio (=e/c) - Newtonian viscosity - standard deviation of the asperity height distribution - dimensionless quantity (=/c) - attitude angle - angle between vertical line and load line - random variable     

Analysis of finite journal bearings with longitudinal and transversal rough surfaces

This paper represents a numerical iterative scheme for calculation of finite 360° journal bearings with longitudinal and transversal rough surfaces. A modified Christensen's Reynolds type equation is solved numerically under isothermal boundary condition. The Reynold's boundary condition assuming that the pressure and its derivative vanish near the point of location of the minimum film thickness is used in an iterative scheme to find out this location. Results of the analysis show the great influence of surface roughness on the bearing behaviour, especially when the bearing operates at its hydrodynamic limit.     

The mechanical behaviour of PEEK short fibre composites

Short glass (GF) and carbon fibre (CF) reinforced poly-ether-ether-ketone (PEEK) composites were prepared by injection moulding and then microstructurally characterized. Their mechanical behaviour was determined by two different methods: a classical unidirectional tensile test and an immersion ultrasonic technique. The reinforcing effect of fibres is discussed in the context of the theory of reinforcement of Bowyer and Bader. Interfacial shear strength and critical fibre length at break are calculated for both PEEK/GF and PEEK/CF composites. Examinations of fracture surfaces of uniaxial tensile specimens revealed a higher adhesion of carbon fibres to PEEK matrix in regards to the adhesion concerning glass fibre-PEEK interfaces, which is in agreement with the results provided by the model. Compatibility of ultrasonic and tensile results is reported.     

Torsional load transfer from a rigid shaft to an elastic plane with a slit

A plane elastostatic problem for an elastic wedge loaded by a concentrated moment at its apex provides an example of violation of the Saint-Venant principle for apex angles 2 larger than . Considering the problem for a truncated wedge, Neuber demonstrated the method of construction of an applicable solution for any apex angles in the range 22, despite the failure of the Saint-Venant principle. In the present paper the particularly important case of the truncated-wedge problem is examined. The truncated wedge degenerates into a slitted elastic plane, while a rigid circular shaft, acted upon by a torsional moment, is inserted into the plane. The analytical solution of the mixed boundary-value problem is obtained. Numerical results turn out to be in complete agreement with Neuber's results for the slitted elastic plane.     

Thermoelastic contact of a rotating shaft with a rigid bush in conditions of bush wear and stick-slip movements

The nonlinear problem of thermoelastic contact of a rotating shaft with a rigid bush fixed to the base elastically (springs) is investigated using both Laplace transform and perturbation methods. A friction coefficient is assumed to be a nonlinear function of a relative velocity. The solution to the problem is reduced to the system of nonlinear differential and integral equations. Zones of steady-state solution stability and friction self-excited oscillations existence are established. The numerical analysis is carried out and some important conclusions are given.     

基于混合均质模型的气液两相流润滑动静压轴承性能分析

依据所建立的从全液体状态经混和介质状态,直至全气体状态的连续汽化流体属性模型,联合广义雷诺方程及全能量方程,从理论上对处在连续变化低温介质条件下的径向动静压轴承的静动特性进行研究。研究结果表明,由于两相流条件下的流体压缩性发生了极大变化,因而使得处在该条件下的轴承性能不再满足全液体或全气体介质润滑下的轴承性能规律。     

Corrosion fatigue short crack growth behaviour in a high strength steel

The influence of an aggressive environment (0.6 M, aerated NaCl solution) on short fatigue crack initiation and growth behaviour has been studied. The study involved three major test series, namely: air fatigue, corrosion fatigue, and intermittent air fatigue/corrosion fatigue. The above tests carried out under fully reversed torsional loading conditions at a frequency of 5 Hz, showed that it was the non-metallic inclusions which took part in crack initiation resulting from debonding at metal matrix/inclusion interface and pitting of inclusions in both air and corrosove environments, respectively. Short fatigue crack growth results in these two environments obtained by using plastic replication technique, indicated a large effect of microstructure i.e. prior austenite grain boundaries. The stage/stages at which the environmental contribution was dominant has been discussed by considering the results achieved from intermittent tests. However, the mechanisms involved in corrosion fatigue short crack growth have also been described in the light of results obtained from futher investigations carried out by conducting corrosion fatigue tests under applied cathodic potential conditions and tests on hydrogen pre-charged specimens under air fatigue and uniaxial tension conditions.     

短切玻璃纤维的分散及其对硬质聚氨酯泡沫塑料性能的影响

研究了不同特性的短切玻璃纤维的分散状况及其对物料黏度、硬质聚氨酯泡沫塑料(RPUF)泡孔结构和力学性能的影响.结果表明,玻璃纤维在基体中有单丝、小束(每束10～40根单丝)和大束(每束300～400根单丝)3种分散状况,其分散状况对物料黏度、RPUF的泡孔结构和力学性能均有明显影响.     

具有轴承不对中故障的柔性非圆截面多转子系统非线性动力学行为

研究了具有轴承不对中故障的柔性非圆截面多转子系统的非线性动力学特性。首先在长轴承、微小不对中量和不平衡量等假设下,利用坐标变换推导出非圆截面多转子-轴承系统的非线性动力学模型。最后采用数值方法,重点分析了系统的非线性振动行为,例如稳态响应、轴心轨迹、Poincaré截面以及最大Lyapunov指数等。结果表明:在较低转速时,转子系统除存在与不平衡故障同步的工频外,还存在由于不对中引起的倍频以及组合频率成分等。随着转速的提高,系统出现倍周期分叉现象,混沌运动等复杂的非线性动力学行为。     

The influence of crack size on the fracture behaviour of short cracks

Crack size effects are investigated by applying local fracture criteria at a specific distance ahead of a crack tip, related to the material's microstructure. For sufficiently long cracks, the criteria are applied at points within the singularity-dominated region and then failure corresponds to the attainment of a critical intensity of the singularity but for shorter cracks this may not be the case and size effects may be anticipated.Comparisons of stress and strain fields around crack tips are made between cracked specimens and a boundary layer model which allows for a finite T-stress parallel to the line of the crack; these demonstrate that size effects can be characterized, for a useful range of crack sizes, in terms of the elasticT-term.The variation of the ductile-brittle transition temperature with crack size is studied on the basis of model calculations based on a power-law hardening material with temperature-dependent yield stress, coupled with two competing fracture criteria, chosen to model brittle or ductile crack extensions respectively. Generally, shorter cracks display lower transition temperatures and higher toughness. This potentially beneficial effect may, however, be nullified by stress triaxiality.     

Hydrodynamic effects of shaft surface roughness on rotary lip seal behaviour

Richard F. Salant and Dawei Shen, Georgia Institute of Technology, Atlanta, Georgia, USAThe early pioneer of research on elastomeric rotary shaft lip seals was the late Dr Ernest Jagger. During the 1960s, he demonstrated the existence of the lubricating film under the seal and proposed methods of load support and film control. Modern computing power has permitted a detailed theoretical study, much of which helps to confirm many of Jagger’s ideas. Research has now progressed to a stage where the shaft surface roughness can also be considered. This feature article, based on a paper originally presented at the International Sealing Conference, Stuttgart in September 2002, describes some of these studies.     

Investigation of tribological properties of boronized Fe-based SAE 1020 and TS-DDK 40 journal bearings at high loads

In practice, ferrous based materials are not used because they show similar properties to shaft material and are known to cause adhesive wear in journal bearings. With boronizing process, adhesive wear can significantly be decreased. In this study, boronizing has been applied to some ferrous based (SAE 1020, TS-DDK 40) journal bearings. Wear experiments were done on SAE 1050 steel shaft as counter abrader with 100 N loads, and 1500 rpm for 5 h by using a radial journal bearing test rig. Boronizing treatment increased wear resistance of SAE 1020, TS-DDK 40 about 10–25, and 5–7 times respectively.