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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.

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.

Computational fracture mechanics based FATIG3D program was used to simulate contact fatigue life of rough surface contacts in boundary to mixed lubrication regimes. Two-rollers contact fatigue tests were conducted and test results were compared with calculated contact fatigue lives. Calculated contact fatigue life agreed with test results well with the selected set of input data. The effect of several important parameters in the input data on contact fatigue life was evaluated computationally using FATIG3D. These parameters include: oil pressure distribution, crack face friction, direction of friction, friction coefficient, initial crack length, Hertzian stress, and residual stress distributions. The results obtained in this work improved basic understanding and the application of FATIG3D in simulating contact fatigue behavior.

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.

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.

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.

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.

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.

Prediction of fatigue performance of large structures and components is generally done through the use of a fatigue analysis software, FEA stress/strain analysis, load spectra, and materials properties generated from laboratory tests with small specimens. Prior experience and test data has shown that a specimen size effect exists, i.e. the fatigue strength or endurance limit of large members is lower than that of small specimens made of same material. Obviously, the size effect is an important issue in fatigue design of large components. However a precise experimental study of the size effect is very difficult for several reasons. It is difficult to prepare geometrically similar specimens with increased volume which have the same microstructures and residual stress distributions throughout the entire material volume to be tested. Fatigue testing of large samples can also be a problem due to the limitation of load capacity of the test systems available.

To improve fuel economy and possibly reduce product cost, light weight and high power density has been a development goal for commercial vehicle axle components. Light weight materials, such as aluminum alloys and polymer materials, as well as polymer matrix composite materials have been applied in various automotive components. However it is still a huge challenge to apply light weight materials in components which are subject to heavy load and thus have high stresses, such as gears for commercial vehicle axles or transmissions. To understand and illustrate this challenge, in this paper we will report and review the current state of art of carburized gear steels properties and performance.

Wave propagation in a fuel line bounded on one end by a pressure regulator creating a constant head and on the other by a single fuel injector creating a time dependent flow rate is studied. It is found that a model consisting of a linearized wave equation and a linearized injector/fuel line boundary condition (including lumped damping) is convenient for analytical work. A general closed form solution of the pertinent equations can be found in terms of a recursion relation which holds for any injection history. Representative solutions are reported for sinusoidal and step function (sudden injector opening or closing) injection histories. Solutions for step function histories are superimposed to create predictions for a variety of periodic (but nonsinusoidal) injection histories. It is found to be possible to extract limiting steady state solutions from these general transient results.

Locati method is suitable in preliminary fatigue tests and production quality control. It is efficient since it uses just one test sample. The method requires that the slope of the S-N curve be known a priori, however. In this paper, a modified Locati method is presented that virtually eliminated this requirement. The method produces a point on the S-N plane that is independent of the slope of the S-N curve. The test design strategy to control the fatigue life of such a point is provided. The presented method has been successfully applied to preliminary fatigue tests of several welded components of ground vehicles.

The objective of this work is to test and develop monotonic tensile properties and strain controlled fatigue properties of a cast ductile iron. The test data and the related material constants will be used in conjunction with vehicle loading data to perform finite element stress-strain analysis and fatigue life prediction analysis to aid in the design of automotive components made from ductile iron. Currently, such material property data does not exist in the literature for this particular grade of ductile iron. Monotonic tension and fully reversed strain controlled fatigue tests were conducted by following ASTM E-8, ASTM E-606, and SAE J-1099 on samples machined from the cast ductile iron. Monotonic tensile properties were obtained, including Young's modulus, yield strength, ultimate tensile strength, elongation, reduction in area, strength coefficient K, and strain hardening exponent n.

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.

This paper discusses the virtual development process used to support design of a high-tonnage hydroform press. It also discusses the optimized design for structural integrity while achieving low target cost. Other considerations included optimization of setup issues such as press fabrication and assembly. Due to tightly constrained development time, a diverse range of CAE methodologies were used to refine and validate the design. Detailed linear and nonlinear finite element models were developed to provide the required accuracy in the critical regions of the press structure. From these detailed models simplified analytical tools were developed to calculate the key press parameters such as alternating stress and predicted fatigue life. Finite element models were validated with physical strain gage measurements from an array of strain gages installed on the production presses.

Current trends in vehicle development, including both automotive and commercial vehicles, are characterized by short model life cycles, reduced development time, concurrent design and manufacturing development, reduced design changes, and reduced total cost. All of these are driven by customer demand of higher load capacity, reduced weight, extended durability and warranty requirement, better NVH performance and reduced cost. These trends have resulted in increased usage of computational simulation tools in design, manufacturing, and testing, i.e. virtual testing or virtual prototyping. This paper summarizes our work in virtual testing, i.e. fatigue life simulations using computational fracture mechanics for commercial vehicle axle gearing development. First, fatigue life simulation results by using computational fracture mechanics CRACKS software were verified by comparing with gear teeth bending fatigue test data and three point bending fatigue test data.