Rolling of I-section beams using lead as a model material: Some experimental results

Results of a series of tests rolling I-section beams in the first two passes, using lead as a model material, are presented; they include measurements of relative spread, natural elongation, roll load, roll torque and the observed changes in deformation modes with variation in shape factors (height to width ratios) of the specimens and the relative draughts.A comparison of these results is made with those obtained using empirical formulae suggested by earlier research workers. The observed rolling loads are compared also with measurements made of the die loads when rectangular specimens with the same shape factors as in these rolling tests were compressed between shaped dies having grooves similar to that in rolling and compressed under conditions of plane strain and in open-die compression.     

Large deflection of a circular C-shaped spring

The theoretical analysis of a circular $\text{C-}\text{shaped}$ spring is presented. The analysis is based on the assumptions that the spring is perfectly elastic and that its deflection is plane under large deflections. The deformed shape of the spring is found to be a segment of a nodal elastica, and the load-deflection curve is almost linear over some range of deflection; this provides basic information for the design of the spring. Experimental verifications are performed using steel circular $\text{C-}\text{shaped}$ springs of flat rectangular cross section. There is no discrepancy between the calculated and observed results.     

212 transmission electron microscopy applied to phase transformations in ball bearings

$\text{2}\text{1}\text{2}$D transmission electron microscopy has been applied to rolling contact-fatigued ball bearings. The $\text{2}\text{1}\text{2}$D technique implies that correlations between image features and the object lattice structure are transformed to a stereoscopic effect, using defocused dark-field image pairs. During contact fatigue, the martensite matrix may decay and be transformed to new phases. Particularly, a carbon-enriched phase has been studied. The findings indicate areas of probable nucleation sites and areas being dilated due to internal stresses. The phase is constituted of a lattice structure with minor and regular variations in the g-vector, involving vector orientation and magnitude.     

High resolution images of a reconstructed surface structure on (111) gold platelets: Interpretation and comparison with theoretical models

Reconstruction of the (111) gold surface has been previously observed, and it has been shown that the surface net is compressed in the <110> direction, as compared with the bulk lattice. We present here some high resolution studies made on this surface reconstruction: the problem was to obtain a structure image corresponding mainly to the uppermost plane which forms the surface. For this, we have formed high resolution images by interferences between the so-called forbidden diffracted beams $\text{1}\text{3}$ (4?22): bulk gold, when observed along the <111> direction, is better described as a stacking of hexagonal two-dimensional layers, and the $\text{1}\text{3}$ (4?22) beams occur as diffracted beams from 1 (or2) hexagonal layers; they nearly disappear every 3 slices. If the top layer is reconstructed, the diffracted beams from the first slice will be different and will not cancel with the diffracted beams from the bulk layers. Hence the image formed with these beams will give some information on the reconstructed top layer. Computed images have been obtained for different models of the reconstructed surface. They show that, indeed, images obtained under these conditions are linked with the topography of the surface. They also show the importance of different experimental parameters, in particular the beam divergence.     

Energy conservation in stainless steel cold rolling applications

In order to predict the performance of rolling oils in actual production mills, from tests in laboratory mills, the influence of various factors, such as shape factors work roll diameter (D), strip thickness (h₁), operating conditions (reduction rate (r), peripheral velocity of roll (U₀), strip velocity (U₁)) and kinematic viscosity of the rolling oil (υ₀) was investigated. A parameter RLI (Rolling Lubrication Index = u₀(U₀+U₁)(1−r)(D/2h₁.r)^½) was found to be useful in predicting lubricating conditions in actual production mill applications. The coefficients of friction of mineral oils, some synthetic hydrocarbons including polybutene, and several kinds of additives were obtained from laboratory mills under the same condition of RLI value as that for finish rolling in actual production mills. With hydrocarbons, paraffins showed the lowest coefficient offriction, while aromatics exhibited a higher coefficient of friction, with naphthenes showing the highest. A high-quality rolling oil was formulated using a combination of ester and paraffinic mineral oil. It is observed that this new oil can save 14% of energy consumed by a laboratory mill compared with conventional rolling oils. In production mills, nearly the same energy conservation level can be achieved.     

A tension-torsion machine for testing yield criteria and stress-strain relationships at T = 78°K

A tension-torsion machine in which aluminium and copper specimens are pulled and twisted while being immersed in liquid nitrogen is described. The incorporated load cell and extensometer offer very accurate readings at $\text{T = 78°}\text{K}$.The test materials are especially treated to approach conditions of isotropy and homogeneity. Stress-strain curves in simple tension and pure shear are obtained at $\text{T = 292°}\text{K}$ and $\text{T = 78°}\text{K}$. It can be seen that at 78°K the initial yield surface obeys the von Mises yield criterion.     

A vectorial method using combination theory in the term 2Wi × Vrel to calculate the acceleration of a point in the space kinematics of rigid bodies

This study to calculate the acceleration of a point using combination theory for compound accelerations constitutes a new interpretation of the general relative acceleration equation. The advantages of this new approach are the easy tabulation and the simple order of the solution and the preservation of the physical concepts. Also, the student has the opportunity to distinguish between $\text{2w}{}_{\mathrm{i}}\text{× V}{}_{\mathrm{<mtext>rel</mtext>}}\text{and}\text{2W × V}{}_{\mathrm{P/M}}$, the Coriolis acceleration. This distinction is useful in avoiding an erroneous physical interpretation.     

A friction model based on the upper-bound approach to the ridge and sublayer deformations

A theory of friction during the steady state sliding of metals is developed on the basis of the upper-bound method, and it focuses on the energy consumed by the relative motion of materials. The sublayer's deformations, the apparent Coulomb (Amontons) coefficient of friction for moderate loads and the constant friction factor for excessive loads are determined as functions of the nominal normal pressure $\text{p}\text{σ}{}_0$, the interface friction factor m₀ and the wedge angle α₁. Furthermore, a criterion for steady state sliding is offered through the optimization process. The results appear to be consistent with a number of published observations.     

The use of finite element creep solutions to obtain J integrals for plane strain cracked members

Numerical values are obtained for the path independent $\text{J}$ integral and for crack opening displacement δ, for internally and externally cracked tension members under conditions of plane strain. These parameters have been obtained, for an $\text{n-}\text{power}$ creeping material, from stationary state solutions using the finite element method. Values of $\text{J}$ and δ are compared with available results and are shown to be in good agreement.     

A theory of plastic anisotropy based on a yield function of fourth order (plane stress state)—I

It is shown from various view points that many of the disadvantages of the conventional theory based on a quadratic yield function can be satisfactorily removed by the use of a yield function of fourth order. Incremental equivalent strain $\text{d}\text{?}{}_{\mathrm{eq}}$is defined by $\text{d}\text{?}{}_{\mathrm{eq}}\text{=σ}{}_{\mathrm{ij}}\text{d}\text{?}{}_{\mathrm{ij}}\text{σ}{}_{\mathrm{eq}}$, and cannot generally be expressed simply by the strain increment components d?_ij. In contrast with the conventional theory, coefficients in the yield function f cannot be determined from the r-values only in uniaxial tensile tests, but yield stresses in these tests and for example in an equi-biaxial tension for the same $\text{}\text{?}\text{ge}{}_{\mathrm{eq}}$ are also required. This fact ensures that the $\text{σ}{}_{\mathrm{eq}}\text{?}\text{?}{}_{\mathrm{eq}}$ curve for arbitrary loading is uniquely determined by the uniaxial tension curve in the rolling direction (R.D.), and thus such an intrinsic difficulty of the conventional theory as dependence of the $\text{σ}{}_{\mathrm{eq}}\text{?}\text{?}{}_{\mathrm{eq}}$ curve on types of loading does not arise. Some formulae for the determination of the coefficients in f are given. Relationships between types of earing in axi-symmetrical deep-drawing and the coefficients of f are examined in detail and it is emphasized that only very special cases are included in the conventional yield function and thus use of it is very limited.     

Wear in electroerosion printing

Two wea$\text{\$}\text{?}$mechanisms are postulated for the wear of an electroerosion print element: abrasive wear as a result of sliding against the electrosensitive paper and electrical discharge wear as a result of the arc developed during the printing process itself. The relative significance and dependences of these two modes were investigated by means of abrasive wear testing and controlled printer tests. It was concluded that for typical printing situations the electrical discharge mode is the predominant mode and the abrasive action of the paper is associated with the abrasives in the undercoat layer of the paper. A model is proposed for the wear process and compared with experimental data.     

Deflexion of a roller compressed between platens

The model of a roller compressed between platens is used to compare the various theories giving roller bearing deflexion. By experiment, it is shown that the formula quoted by Palmgren, $\text{2}\text{x}\text{= 7.62}\text{w}{}^{\mathrm{(0.9)}}$, is the most appropriate for normal roller application.     

Mean separation and real contact area between surfaces pressed together under high static loads

The mean separations for tin, aluminium and silver rough surfaces pressed beneath a horizontal flat silver-steel anvil by high loads, disagreed with predictions from Tsukizoe and Hisakado theory, which incorrectly assumes that the real contact area equals the applied pressure P divided by the micro-hardness M of the softer contacting material. The point of initial contact (or zero penetration) corresponded to the truncation of surface heights at t = 3.5, for surfaces having Gaussian distributions, where t is the statistical probability function.At high loads, the real contact area as calculated from experimental separation data, corroborated values obtained from profilometry but disagreed with predictions from classical plastic deformation theory. The real area of contact equalled $\text{K (}\text{P}\text{M}\text{)}{}^{\mathrm{m}}$, where K and m are constants which take different values for each of three load ranges.For plastic deformations, the assumption that the relation between the contact area and the separation can be obtained directly from the bearing area curve can be in error by up to 20% at high loads fi.e. for $\text{P}\text{M}\text{>5 × 10}{}^{\mathrm{?2}}$.     

Surface strength of silicon nitride in relation to rolling contact performance measured on ball-on-rod and modified four-ball tests

Silicon nitride (Si₃N₄) has been used in various rolling contact applications in turbomachinery, automotive and power industry. It is favoured to replace conventional steel due to its low density, low friction, corrosion resistance and good performance under extreme condition. However, a major limitation of its wider application is its high material and machining cost, especially the cost associated with the finishing process. In the present study, a low cost sintered and reaction bonded silicon nitride (SRBSN) is used to study the surface machining effects on its rolling contact performance. Attempt has been made to link the surface strengths of Si₃N₄ derived from half-rod and C-sphere flexure strength specimens to the rolling contact lifetimes of Si₃N₄ rod and ball specimens. The rolling contact fatigue tests are carried out on ball-on-rod and modified four ball machines. Three types of surfaces with coarse, fine and conventional finishing conditions are examined. Flexure strength tests on half-rod and C-sphere show an increasing surface strength from specimens with coarse, fine to conventionally machined conditions. During rolling contact fatigue test of as-machined specimens, there are no failures observed on both ball-on-rod and four ball tests after 100 million stress cycles. However, there is a trend of decreasing wear volumes measured on the contact path of rods and balls with coarse, fine and conventional conditions. In four ball test, spall failures are observed on pre-crack specimens. There is a trend of increasing rolling contact fatigue lifetime from pre-cracked specimens with coarse, fine to conventional machining conditions.     

Real Time TEM Imaging of Compression and Shear of Single Fullerene-Like MoS2 Nanoparticle

The deformation and degradation behavior of single inorganic fullerenes nanoparticles of MoS₂ under compression and shear has been observed in real time using a high-resolution transmission electron microscope equipped with a nanoindentation holder. The MoS₂ nanoparticles were compressed using a nanoindenter and a truncated diamond tip. For the first time, real time imaging of the deformation of individual nanoparticles clearly shows first orientation changes in the particle shape during loading process followed by a large deformation and the exfoliation of the outer sheets of the fullerene nested structure. Exfoliation was observed for a contact pressure estimated at 1 GPa. Additional sliding tests performed with the nanoindenter gave evidence for a rolling process for lower contact pressures up to 100 MPa.     

Rolling contact fatigue performance of detonation gun coated elements

Rolling contact fatigue performance of thermal spray coatings has been investigated using an experimental approach. A modified four ball machine which simulates a rolling element bearing was used to examine the coating performance and failure modes in a conventional steel ball bearing and hybrid ceramic bearing configurations. Tungsten carbide (WC-15% Co) and aluminium oxide (Al₂O₃) were thermally sprayed using a super D-Gun (SDG2040) on M-50 bearing steel substrate in the geometrical shape of a cone. A coated cone replaced the upper ball that contacts with three lower balls. The rolling contact fatigue (RCF) tests were performed under immersed lubricated conditions using two different lubricants. Fatigue failure modes were observed using a scanning electron microscope. Microhardness measurements of the coating and the substrate and elastohydrodynamic fluid film thickness results are included. The results show the requirement for significant optimization of the coating before use in rolling element bearing applications. The coating was fractured in a delamination mode. Test results show an optimization in coating process is required before these coatings can be used for rolling contact applications. WC-Co coatings perform better than Al₂O₃ coatings in rolling contact.     

Elastohydrodynamic films in mixed lubrication: An experimental investigation

Experimental investigations were carried out with a Roxana rolling four-ball tester in the mixed lubrication regime. The electrical resistance technique was used in conjunction with ball profiles taken with a stylus apparatus to gain information about the formation of elastohydrodynamic films between rough surfaces and their evolution during running-in. The results show that rough surfaces in general make thinner films than smooth ones, but if $\text{h}{}_0\text{σ}{}_{\mathrm{h}}\text{> 2}$ roughness has a negligible effect.     

Evaluation of Hot Pressed Silicon Nitride as a Rolling Bearing Material

A series of tests has been conducted to evaluate the suitability of silicon nitride as a bearing material for rolling contact applications. The ability of silicon nitride to be lubricated by some conventional lubricants was found to be satisfactory. This was determined by wettability studies, lubricant film thickness and traction coefficient measurements on the optical EHD rig and friction coefficient measurements by the pin-on-disk method. The abrasive wear coefficient, measured on a lopping machine using 600 grit SiC abrasive, was found to be high compared to other ceramics. It was also dependent on the composition of the silicon nitride. Comparative rolling contact fatigue tests on steel and silicon nitride flat washers were conducted using steel rollers and balls. A high wear rate leading to grooving in the rolling track on silicon nitride was observed. The spalling resistance of silicon nitride was found to be higher than that of steel under the test conditions used. Surface interactions in the Si₃N₄-M50 steel contacts, detrimental to the life of the steel rolling elements, were recognized. Attempts were made to reduce the severity of these interactions and prolong the life of bearings containing ceramic elements.