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TWO TYPES of bench wear tests employed by the General Motors Research Laboratories are described, and examples are given to illustrate the application of the tests to material development problems. It is shown that correlation of a bench test with service may be achieved even when the laboratory test conditions do not appear to duplicate service conditions exactly. It is postulated that this behaviour is related to the formation of certain types of surface films during the wearing process. Some preliminary results are given of a study of the influence of lubricant type and material composition on the formation of anti-wear films.

THE PURPOSE of this experiment was to determine the role of residual stresses in fatigue strength independent of other factors usually involved when residual stresses are introduced. It consisted of an investigation of the influence of residual stresses introduced by shotpeening on the fatigue strength of steel (Rockwell C hardness 48) in unidirectional bending. Residual stresses were varied by peening under various conditions of applied strain. This process introduced substantially the same amount and kind of surface cold working with residual stresses varying over a wide range of values. It was found that shotpeening of steel of this hardness is beneficial primarily because of the nature of the macro-residual-stresses introduced by the process. There is no gain attributable to “strain-hardening” for this material. An effort was made to explain the results on the basis of three failure criteria: distortion energy, maximum shear stress, and maximum stress.*

PEARLITIC malleable iron crankshafts are being used in the new Pontiac engine as a result of recent developments. This paper discusses the physical properties of pearlitic malleable iron such as elastic modulus, fatigue endurance, and tensile strength. According to the author, definite machining economies result from using pearlitic malleable iron crankshafts.

Four multigrade engine oils, containing the same base oil plus SE additive package but VI improvers of differing shear stability, were evaluated in 80 000 km of high-speed, high-temperature vehicle service. Bearing, piston ring and valve guide wear, as well as oil consumption, oil filter plugging and engine cleanliness were all worse for the engines operated on the low-shear stability oils. The wear differences were traced to differences in high-shear-rate viscosity, while the cleanliness, filter plugging and oil consumption differences occurred because of excessive wear or polymer shear degradation. These results suggest that engine oil viscosity should be specified under high-shear-rate conditions.

The search for improvements in occupant protection under vehicle impact is hampered by a real lack of reliable biomechanical data. To help fill this void, General Motors has initiated joint research with independent researchers such as the School of Medicine, U. C. L. A. – in this case to study localized head and facial trauma — and has developed such unique laboratory tools as “Tramasaf,” a human-simulating headform, and “MetNet,” a pressure-sensitive metal foam. Research applied directly to product design also has culminated in developments such as the Side-Guard Beam for side impact protection.

The strain-life approach is now commonly used for fatigue life analysis and predictions in the ground vehicle industry. This approach requires the use of material properties obtained from strain-controlled uniaxial fatigue tests. These properties include fatigue strength coefficient (σf′), fatigue strength exponent (b), fatigue ductility coefficient (εf′), fatigue ductility exponent (c), cyclic strength coefficient (K′), and cyclic strain hardening exponent (n′). To obtain the aforementioned properties for the material, raw data from stable cyclic stress-strain loops are fitted in log-log scale. These data include total, elastic and plastic strain amplitudes, stress amplitude, and fatigue life. Values of the low cycle fatigue properties (σf′, b, εf′, c) determined from the raw data depend on the method of measurement and fitting. This paper examines the merits and influence of using different measurement and fitting methods on the obtained properties.

In 1985, the Body Division of the Automotive Corrosion and Prevention Committee of SAE (ACAP) concluded that an automotive body corrosion survey for public consumption was needed. The committee proceeded to develop a survey methodology and conducted surveys in the Detroit area every second year starting in 1985. The survey is a closed car parking lot survey of nineteen panels or partial panels checking for perforations, blisters and surface rust. Similar surveys have and will continue to be conducted at biyearly intervals for comparison purposes to track the results of industry wide corrosion protection “improvements”. This is a report of the results of the first three surveys. THE ACAP COMMITTEE BODY DIVISION has now completed the third in its series of biyearly surveys. It is now possible to see some very clear results of industry actions and some indication of future performance.

Since 1985, the Body Division of the Automotive Corrosion and Prevention Committee of SAE (ACAP) has conducted biannual surveys of automotive body corrosion in the Detroit area. The purpose of these surveys is to track industry wide corrosion protection improvements and to make this information available for public consumption. The survey consists of a closed car parking lot survey checking for perforations, blisters, and surface rust. This paper reports the results of the five surveys conducted to date.

The Body Division of the Automotive Corrosion and Prevention Committee of SAE (ACAP) has conducted biannual surveys of automotive body corrosion in the Detroit area since 1985. The purpose of these surveys is to track industry-wide corrosion protection improvements and to make this information available for public consumption. The survey consists of a closed car parking lot survey checking for perforations, blisters, and surface rust. This paper reports the results of the seven surveys conducted since 1985.

The effect of compaction and fiber volume fraction on the transverse permeability of a fluid flowing through stacked layers of fiber mats has been experimentally studied. A Unifilo-101 random mat of continuous glass strands, held together with a binder soluble in styrene was used. The stacked layers were compacted using a Wabash instrumented press. Changing the maximum load, resulted in different fiber volume fractions. Mixtures of glycerol and water with viscosities between 85 and 100 mPa-s were used. This fluid is passed in a rectangular cell, through the fibers arranged transverse to the direction of flow. The pressure drop across the mat and the flow rate were monitored. The study was carried out at different flow rates of the fluid and was repeated for other fiber volume fractions. A power-law relation was observed between the permeability and the fiber volume fraction.

This paper reports on the experimental study of carbide and polycrystalline diamond (PCD) drills used for drilling composite/titanium stacks. Materials systems used in this study were multi-directional carbon fiber in an epoxy matrix and titanium 6Al-4V. The drill materials included tungsten carbide (WC; 9%Co ultra fine grain) and polycrystalline diamond (PCD; bimodal grade). Torque and thrust force were measured during the drilling experiments. Tool wear of both drills was periodically examined during the drilling tests using various microscopic techniques such as optical and Scanning Electron Microscope (SEM). Effect of tool materials and process condition on hole quality parameters such as hole diameter, surface roughness, and titanium burrs, were examined. Dissimilar mechanical and thermal properties of the stacks affected the tool life and resulted in the decreased hole quality for both cutting tool materials, although to a differing degree.

The thermal durability of a large frontal area cordierite ceramic wall-flow filter for light-duty diesel engine is examined under various regeneration conditions. The radial temperature distribution during burner regeneration, obtained by eight different thermocouples at six different axial sections of a 75″ diameter x 8″ long filter, is used together with physical properties of the filter to compute thermal stresses via finite element analysis. The stress-time history of the filter is then compared with the strength and fatigue characteristics of extruded cordierite ceramic monolith. The successful performance of the filter over as many as 1000 regenerations is attributed to three important design parameters, namely unique filter properties, controlled regeneration conditions, and optimum packaging design. The latter induces significant radial and axial compression in the filter thereby enhancing its strength and reducing the operating stresses.

A need to develop methodologies to obtain objective measurements of the effects of different seat contours on people is evident. In an effort to monitor muscle activity during static seated postures, electromyography (EMG) was employed. In an experimental setting, fatigue was induced in back extensor muscles for different seated postures. The resultant EMG signals were then sampled bilaterally for three different vertebral levels and the effects of the different seating systems on posture were evaluated. In preliminary tests involving 4 subjects of similar size and build, utilizing three differently contoured seats, findings support the use of EMG to quantify muscular fatigue as a viable means of objectively measuring the effects of different seat contours.

A detailed description of the oxidative stability of GM's DEXRON®-VI Factory Fill Automatic Transmission Fluid (ATF) is provided, which can be integrated into a working algorithm to estimate the end of useful oxidative life of the fluid. As described previously, an algorithm to determine the end of useful life of an automatic transmission fluid exists and is composed of two simultaneous counters, one monitoring bulk oxidation and the other monitoring friction degradation [1]. When either the bulk oxidation model or the friction model reach the specified limit, a signal can be triggered to alert the driver that an ATF change is required. The data presented in this report can be used to develop the bulk oxidation model. The bulk oxidation model is built from a large series of bench oxidation tests. These data can also be used independent of a vehicle to show the relative oxidation resistance of this fluid, at various temperatures, compared to other common lubricants.

General Motors Powertrain Division has developed a new V-8 engine for Cadillac vehicles in the 1990s. The Northstar engine incorporates the use of aluminum for both the cylinder block and head and other lightweight materials throughout. The valve train incorporates direct acting hydraulic lifters actuating the four valves per cylinder through dual overhead camshafts. The primary focus of the project has been to produce an engine of unquestioned reliability and exceptional value which is pleasing to the customer throughout the range of loads and speeds. The engine was designed with a light weight valve train, low valve overlap and moderate lift, resulting in a very pleasing combination of smooth idle and a broad range of power. The use of analytical methods early in the design stage enabled systems to be engineered to optimize reliability, pleaseability and value by reducing frictional losses, noise, and potential leak paths, while increasing efficiency and ease of manufacture.

Flame spread over a melting thermally thick composite polymer is investigated in a channel flow above a condensed fuel. The condensed fuel consists of an isotropic (melted layer of) liquid near the heated surface and an anisotropic (not-yet-melted) solid surrounding it. The influence of the solid anisotropy is evaluated by changing the solid conductivity (ksx or ksy) in one particular direction (x in horizontal flame spread direction or y in vertical direction, see schematics in Figure 1) while keeping the other properties fixed. Note that the liquid conductivity kl has no isotropic behavior. Numerically, it is found that the flame spread rate decreases with either increasing ksx or ksy. The decrease with respect to ksy is less than for a comparable case described by the de Ris formula for an isotropic pure solid. The flame spread rate is more accurately determined by an analytical formula derived for spread across a melting solid fuel.

This study evaluated multi-layer steel and composite head gaskets of various thicknesses (0.43 to 1.5 mm) and fire-ring diameters to determine the influence of head gasket crevices on engine-out hydrocarbon (HC) emissions. The upper limit in the percent reduction in HC emissions from gasket-design modifications is estimated to be about 15%. At part-load conditions, the lowest HC emissions were measured for head-gasket thickness of about 1 mm. Significantly smaller thicknesses of the order of 0.4 mm result in an increase in HC emissions. Substantial hydrocarbon-emissions advantage may be realized by minimizing the gasket-to-cylinder bore offset.

This paper presents a study of the effects of a resin soluble thermoplastic preform binder on the Resin Transfer Molding (RTM) process. The focus of the study is the rate of dissolution of the binder in the resin and the associated viscosity changes in the resin. Tests on the rate of binder dissolution from continuous strand glass mats show that after one minute of exposure to styrene, roughly half of the medium solubility binder from Unifilo 750 will dissolve and all of the high solubility binder from Unifilo 101 will dissolve. As the concentration of binder in the resin increases from 0 to 5 wt. percent, the viscosity of a vinyl ester resin increases from 125 cps to 280 cps. The viscosity of the resin has also been monitored in continuous flow experiments through the mats placed in a rectangular plague mold, at different flowrates. In these runs, the viscosity varied from 245 mPa-s to 145 mPa-s when the fill time was 2.2 minutes.

Diesel exhaust gas dilution and odor intensity were measured in the immediate vicinity of a transit bus equipped with a rear-mounted horizontal exhaust pipe, a rear-mounted vertical exhaust pipe, and a roof-top diffusion system. Exhaust dilution ratios were measured indoors during vehicle idle operation, using propane added to the exhaust gas as a tracer. Exhaust odor intensities were measured also indoors during vehicle idle operation by a human panel, using a threshold odor measurement technique. On the average, the dilution of the exhaust gas around the bus with the vertical exhaust pipe was about eight times greater than it was with the horizontal pipe. Odor intensity, as measured by the threshold response distance, was about 35% less with the vertical pipe than with the horizontal pipe. The roof-top diffuser was not as effective as the vertical exhaust pipe in increasing exhaust gas dilution or in reducing exhaust odor intensity.

A selection of commercially available chromium and chromium-free post phosphate rinses along with a deionized water rinse were evaluated over several zinc and zinc-alloy coated sheet steels. The test specimens were pretreated and electrocoated on-line in an automotive assembly plant. The effect of the rinse treatments on the cosmetic corrosion performance of the substrates, after 5 years of exposure in an outdoor scab corrosion test was determined. After this exposure none of the rinse treatments had performed better than deionized water rinse on zinc and zinc-iron coated sheet. The zinc-nickel coating showed improved scribe creepage when treated with the Cr+6/Cr+3 rinse. Data is provided comparing the concentration of the treatments used vs scribe creepage and chipping corrosion paint loss.