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Fatigue testing of components is used to validate new product designs as well as changes made to existing designs. On new designs it is common to initially test parts at the design stage (design verification or DV) and then again at the production stage (production verification or PV) to make sure the performance has not changed. On changes to existing designs typically the life of the new part (B) is compared to that of the old part (A). When comparing the fatigue life Weibull analysis is normally used to evaluate the data. The expectation is that the B10 or B50 life of the new part or PV parts should be equal to or better than that of the old parts or the DV parts. However, fatigue testing has a great deal of inherent variability in the resulting life. In this paper the variability of numerous carburized and induction hardened components is examined.

A new wheel end concept was designed and developed to allow sport utility vehicles (SUV) and light trucks the possibility of achieving a negative scrub radius. This paper will compare a production vehicle with a scrub radius of 54.8 mm with the same vehicle modified with several alternate scrub radii. The vehicle changes are completed in a way that still packages the brake components and meets the component durability needs of a light truck wheel end load cycle. Quantitative vehicle computer analysis and actual instrumented vehicle performance data will be compared and correlated to analyze the effects of scrub radius.

As a part of a major research program with the aim of improving heavy truck drive axle fuel efficiency, this work focuses on seal friction torque test development and establishing pinion seal and wheel seal friction torque baseline data. Pinion seal and wheel seal friction torque was measured. The effect of speed and temperature on pinion seal friction torque was assessed. The effect of several coatings on pinion seal friction torque was evaluated. Pinion seal friction torque was also calculated and calculation result was compared with test data. Finally the impact of seal friction and bearing friction on total drive axle power loss was discussed.

Microwave plasmas at atmospheric pressures can be utilized for carburization of steel alloys. Due to their high frequencies, microwaves ionize and dissociate molecules with great efficiency and provide carbon for carburization by dissociating hydrocarbons that are introduced in the plasma. Also, conventional carburization techniques are not very energy efficient, as much of the heat generated is not utilized for the heating of the parts. Microwave plasmas are highly energy efficient due to very high coupling of microwaves to the plasma and then transferring of heat to the parts. Since plasma surrounds the part uniformly, heating rates over the part surface are also uniform. Preliminary results are presented for carburization of steel alloy 8620H by atmospheric microwave plasma process using acetylene as the source gas. Possible effects of application of pulsed DC bias to the parts are also discussed.

A series of bending fatigue tests were conducted and S-N data were obtained for two groups of 4320 steel samples: (1) carburized, quenched and tempered, (2) carburized, quenched, tempered and shot peened. Shot peening improved the fatigue life and endurance limit. The S-N data exhibited large scatter, especially for carburized samples and at the high cycle life regime. Sample characterization work was performed and scatter bands were established for residual stress distributions, in addition to fracture and fatigue properties for 4320 steel. Moreover, a fatigue life analysis was performed using fracture mechanics and strain life fatigue theories. Scatter in S-N curves was established computationally by using the lower bound and upper bound in materials properties, residual stress and IGO depth in the input data. The results for fatigue life analysis, using either computational fracture mechanics or strain life theory, agreed reasonably well with the test data.

Traditional methods often lead to truck component designs that are overly conservative. The ever-increasing need to reduce operational costs demands innovative means for producing parts that are light, durable and capable of carrying more loads. This paper discusses the far-reaching advantages of shape-optimization, beyond the fundamental stipulation of weight reduction. A suspension link is considered to demonstrate the benefits of an optimally shaped component.

Improvements in component/system design is a daily challenge these days, always looking for high performance, reduced mass and low costs. The source for the best fit between these factors, coupled with adequate durability performance, is crucial to the success of a given product and this is what motivates engineering teams around the world. The demand for efficient projects with short deadlines for validation and certification is huge and simulation tools focused on accelerated durability and virtual validation are increasingly being used. When developing a new spring for commercial vehicles, lessons learned from the actual loads applied to the suspension are the “key” to a successful project. The loads/stresses from the ground (vertical loads, lateral loads, longitudinal and braking loads) are quite high and, consequently, relevant to the proper definition of the design of the suspension components.

The method presented utilizes the analytical design model and matrix algebra to determine the load required to close a design gap. By performing a linear analysis in MSC® Nastran, relative displacements at fastener contact points due to unit loading are collected. The stiffness equation, F = K x is used in matrix form to determine gap closure force. The effect of this force on preload should be considered in torque specifications. The method prevents overestimation of preload if closure force is not considered and underestimation if only the stiffness equation is used independently.

Shaft surface texture plays a very important role in rotary oil seal system performance. Functionally, the shaft surface has to prevent oil leakage via pumping between the shaft and seal. The shaft surface texture must also provide adequate contact with the seal lip, while maintaining a lubricant film. Furthermore, the initial surface texture of the shaft plays a vital role in the process of oil seal lip break-in. The shaft surface finish specification is typically Ra, 10 to 20 μ″ with a 0° ± 0.05°lead angle. The paper will describe a new surface measurement method based on interference microscopy, which generates a visual representation of a significant portion of the shaft surface texture to allow direct lead angle detection. Using this new technique, this paper will demonstrate the heredity of lead generation. The shaft 3D surface texture measurement also provides a measure of the surface volume available for lubricant retention.

This paper will describe the development of an accelerated testing methodology for an off-highway vehicle rotary oil seal system. There are two typical field failure mechanisms associated with off-highway input pinion shaft oil seals: 1) excessive abrasive wear of soft seal lip and hard shaft surface due to abrasive environment; 2) excessive heat and degradation of the seal lip due to lack of lubricity and wear of the shaft surface run against this seal. The accelerated testing of the rotary oil seal consisted of a combination of the following factors; shaft run-out, eccentricity, testing temperature, rotation and reciprocal motion of the seal lip relative to the shaft surface. The combination of these factors especially reciprocal motion reproduces the same failure mechanism, i.e. shaft wear grooves and oil seal lip wear observed on the field usage samples with 6,300 hours service in only 350 hours of accelerated testing.

Vehicular suspension ball joints can be categorized in the family of tribological systems which can reduce useful service or working capacity through malfunction or breakdown. Detailed metallurgical analysis of the friction and wear mechanisms on typical ball joint bearing surfaces point to a Teflon-based woven fabric, self-lubricating liner as the best bearing material for the joint. Laboratory functional testing was conducted on modern, 4-axis test equipment simulating the applicable loading and motion conditions typically encountered in use. The self-lubricated bearing liner woven with Teflon thread demonstrated higher sustained load capacity, less rotating friction, excellent torque retention qualities and extended life in comparison to existing components utilizing greased metal-on-metal and/or “plastic” bearing materials.

A nano-composite high strength (NCHS) steel was tested and evaluated in this work. Monotonic tension, strain controlled fatigue and fracture toughness tests were conducted at ambient temperature. Chemical composition, microstructure and fractography analysis were also performed. The NCHS steel showed excellent combination of high strength, high ductility and high fracture toughness with relatively low alloy content, compared with a S7 tool steel. Fatigue performance of the NCHS steel was also better than that of S7 tool steel. With the exceptional combination of high strength and high fracture toughness, the nano-composite high strength steel may have potential applications in gears, shafts, tools and dies where high fatigue performance, shock load resistance, wear and corrosion resistance is required.

The main objective of this paper is to investigate contact fatigue life models and to evaluate the effect of surface finish on contact fatigue life. The effect of surface finish on contact fatigue life was investigated experimentally using two roller contact fatigue tests. The test samples, i.e. rollers, were carburized, quenched and then tempered. Two different roller surface finishes were evaluated: machined and as heat-treated surface (baseline rough surface) vs. super finished surface (smooth). Because many factors are involved in sliding/rolling contact fatigue, contact fatigue modeling is still in the early development stage. In this work, we will analyze our contact fatigue test results and correlate contact fatigue life with several empirical contact fatigue models, such as the lambda ratio, a new surface texture parameter, and a normalized pitting model which includes Hertzian Stress, sliding, surface roughness and oil film thickness.

Finite element modeling has been used extensively nowadays for predicting the noise and vibration performance of whole engines or subsystems. However, the elastomeric components on the engines or subsystems are often omitted in the FE models due to some known difficulties. One of these is the lack of the material properties at higher frequencies. The elastomer is known to have frequency-dependent viscoelasticity, i.e., the dynamic modulus increases monotonically with frequency and the damping exhibits a peak. These properties can be easily measured using conventional dynamic mechanical experiments but only in the lower range of frequencies. The present paper describes a method for characterizing the viscoelastic properties at higher frequencies using fractional calculus. The viscoelastic constitutive equations based on fractional derivatives are discussed. The method is then used to predict the high frequency properties of an elastomer.

Compression is a key design attribute of both compressible seals and coupled hose systems. Traditional design techniques use 3-sigma upper and lower limits from capability studies on critical component dimensions to estimate potential compression variation. Probability calculations are shown that indicate that the true variation in compression is much less than this estimate. An alternative approach using probabilistic design techniques to calculate true 6-sigma (+/-3-sigma) compression variation is shown for both a typical radial seal and a hose coupling. The results are then compared to Monte Carlo simulations using representative data sets for each critical dimension.

Axle primary gearing is normally carburized for high and balanced resistance to contact fatigue, wear, bending fatigue, and impact loading. The focus of this work is on bending fatigue which is a key design consideration of automotive and commercial vehicle axle gearing. Since a carburized component is basically a composite material with steep gradients in carbon content, hardness, tensile strength and microstructure from surface to the middle of the cross section combined with non-linear residual stress, its bending fatigue life prediction is a complex and challenging task. Many factors affect the bending fatigue performance of axle gearing, such as gear design, gear manufacturing, loading history during service, residual stress distribution, steel grade, and heat treatment. In this paper, the general methodology for bending fatigue life prediction of a carburized component is investigated. Carburized steel composites are treated as two homogeneous materials: case and core.

A new proprietary Atmospheric Pressure Microwave Plasma Technology, developed for various materials processing applications, has been applied to P/M sintering of cam lobes. The aims were a) to compare the new processing route with conventional process for the same alloy composition and b) to check the possibility of successful sintering at higher temperatures so that different higher temperature P/M alloys may be used. P/M green cam lobes were used, and sintering runs were carried out initially at temperatures comparable to that currently used in the conventional processes; this was followed by runs at higher temperatures that are not very practical in the conventional processing route due to equipment component constraints. Properties such as density and hardness were measured for the sintered samples, together with corresponding microstructural analysis.

Gear tooth friction directly influences power losses and temperature rise as well as system dynamic behavior. Recently it attracted many attentions as friction is considered one of the main sources of power losses in geared systems, such as in automotive transmissions. Coefficient of friction has been found not a constant but varies with different contact conditions, which partly makes the measurement of friction a difficult and expensive process. Therefore an analytical model that is capable of predicting it accurately becomes very much demanded. A few empirical formulae based on experimental data and analytical models based on lubrication theory are found in the literature. However, they are either not suitable for a general gear contact or too complex to adapt in gearing. In this paper, a new coefficient of sliding friction based on a thermal Elastohydrodynamic Lubrication (EHL) model is developed by a multiple linear regression analysis.