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The susceptibility of Advanced High Strength Steels (AHSS) to hydrogen embrittlement (HE) was evaluated on selected high strength sheet steels (DP 600, TRIP 780, TRIP 980, TWIP-Al, TWIP, and Martensitic M220) and the results were compared to data on a lower strength (300 MPa tensile strength) low carbon steel. Tensile samples were cathodically charged and then immediately tensile tested to failure to analyze the mechanical properties of the as-charged steel. The effects of hydrogen on deformation and fracture behavior were evaluated through analysis of tensile properties, necking geometry, and SEM images of fracture surfaces and metallographic samples of deformed tensile specimens. The two fully austenitic TWIP steels were resistant to hydrogen effects in the laboratory charged tensile samples.

Fracture split forged steel connecting rods are utilized in many new high performance automotive engines to increase durability. Higher strength levels are needed as the power density increases. Fracture splitting without plastic deformation is necessary for manufacturability. Metallurgical design is a key for achieving the required performance levels. Several medium carbon steels containing 0.07 wt pct P, 0.06 wt pct S and various amounts of Mn, Si, V, and N were produced by vacuum induction melting laboratory heats and hot working the cast ingots into plates. The plates were cooled at varying rates to simulate typical cooling methods after forging. Microstructures were generally ferrite and pearlite as evaluated by light optical and scanning electron microscopy. Mechanical properties were determined by standard tensile tests, high strain rate notched tensile tests, and Charpy V-notch impact tests to assess “splittability”.

Quenching and partitioning (Q&P) is a novel heat treatment to produce third generation advanced high-strength steels (AHSS). The influence of carbon on mechanical properties of Q&P treated CMnSi-steels was studied using 0.3C-1.5Mn-1.5Si and 0.4C-1.5Mn-1.5Si alloys. Full austenitization followed by two-step Q&P treatments were conducted using varying partitioning times and a fixed partitioning temperature of 400 °C. The results were compared to literature data for 0.2C-1.6Mn-1.6Si, 0.2-3Mn-1.6Si and 0.3-3Mn-1.6Si Q&P treated steels. The comparison showed that increasing the carbon content from 0.2 to 0.4 wt pct increased the ultimate tensile strength by 140 MPa per 0.1 wt pct C up to 1611 MPa without significantly decreasing ductility for the partitioning conditions used. Increased alloy carbon content did not substantially increase the retained austenite fractions. The best combinations of ultimate tensile strength and total elongation were obtained using short partitioning times.

This work examines the effect of valve timing during cold crank-start and cold fast-idle (1200 rpm, 2 bar NIMEP) on the emissions of hydrocarbons (HC) and particulate mass and number (PM/PN). Four different cam-phaser configurations are studied in detail: 1. Baseline stock valve timing. 2. Late intake opening/closing. 3. Early exhaust opening/closing. 4. Late intake phasing combined with early exhaust phasing. Delaying the intake valve opening improves the mixture formation process and results in more than 25% reduction of the HC and of the PM/PN emissions during cold crank-start. Early exhaust valve phasing results in a deterioration of the HC and PM/PN emissions performance during cold crank-start. Nevertheless, early exhaust valve phasing slightly improves the HC emissions and substantially reduces the particulate emissions at cold fast-idle.

The influence of coatings on fatigue behavior has been examined for the following commercially produced sheet steels: uncoated titanium stabilized interstitial-free (IF); electrogalvanized titanium stabilized IF; hot-dip galvanized aluminum killed, drawing quality (AKDQ); and galvannealed AKDQ. Fully reversed bending fatigue tests were conducted at ambient temperature on Krouse-type flexural fatigue machines. A dependence of crack development was observed and correlated to the microstructure and properties of the different coatings. Furthermore, a functional design relationship for each material was determined through stress-life analysis. The experimentally determined fatigue properties were compared to conventional estimates based on tensile properties which ignore coating effects. The results of this work suggest that ductile coatings may enhance fatigue resistance, while brittle coatings may reduce fatigue life.

The bending fatigue performance of high temperature (1050 °C) vacuum carburized Nb modified 8620 steel, with niobium additions of 0.02, 0.06 and 0.1 wt pct, was evaluated utilizing a modified Brugger specimen geometry. Samples were heated at two different rates (20 and 114 °C min-1) to the carburizing temperature resulting in different prior austenite grain structures that depended on the specific Nb addition and heating rate employed. At the lower heating rate, uniform fine grained prior austenite grain structures developed in the 0.06 and 0.1 Nb steels while a duplex grain structure with the presence of large (>200 μm grains) developed in the 0.02 Nb steel. At the higher heating rate the propensity for abnormal grain growth was highest in the 0.02 Nb steel and complete suppression of abnormal grain growth was achieved only with the 0.1 Nb steel.

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.

This paper presents tribological modeling, experimental work, and validation of tribology parameters of a single cylinder turbocharged diesel engine run at various loads, speeds, intake boost pressures, and cylinder liner temperatures. Analysis were made on piston rings and liner materials, rings mechanical and thermal loads, contact pressure between rings and liner, and lubricant conditions. The engine tribology parameters were measured, and used to validate the engine tribology models. These tribology parameters are: oil film thickness, coefficient of friction between rings and liner, friction force, friction power, friction torque, shear rate, shear stress and wear of the sliding surfaces. In order to measure the oil film thickness between rings and liner, a single cylinder AVL turbocharged diesel engine was instrumented to accept the difference in voltage drop method between rings, oil film, and liner.

The life of an automotive engine is often limited by the ability of its components to resist wear. Zinc dialkyldithiophosphate (ZDDP) is an engine oil additive that reduces wear in an engine by forming solid antiwear films at points of moving contact. The effects of this additive are fairly well understood, but there is little theory behind the kinetics of antiwear film formation and removal. This lack of dynamic modeling makes it difficult to predict the effects of wear at the design stage for an engine component or a lubricant formulation. The purpose of this discussion is to develop a framework for modeling the formation and evolution of ZDDP antiwear films based on the relevant chemical pathways and physical mechanisms at work.

With the increased use of tubular steel products, especially for automotive hydroforming applications, there is increased interest in understanding the mechanical properties measured by tensile tests from specimens of different orientations in the tube. In this study, two orientations of tensile specimens were evaluated -- axial specimens with and without flattening and flattened circumferential specimens. Three steels were evaluated -- two thicknesses of aluminum killed drawing quality (AKDQ) steel and one thickness of high strength low alloy (HSLA) steel. Mechanical property data were obtained from the flat stock, conventional production tubes and quasi tubes. Quasi tubes were produced from the flat stock on a 3-roll bender, but the quasi tube was not welded or sized.

The response of HSLA steel, 590R, and dual-phase steel, DP-600, to non-uniform deformation imposed in a laboratory Bending-Under-Tension (BUT) test apparatus was evaluated. Samples were deformed with both low and high back tension forces at bend angles of 45 and 90 degrees, and evaluated to determine the “side-wall curl”, i.e. the curvature in the sheet section in contact with the die. The results indicate that there are no consistent differences between the two steels, 590R and DP-600. It was found that back tension, tensile strength and sheet thickness were the primary factors affecting curl. The bend angle has an influence on curl, with the curl radius at a 90° bend angle being greater than the curl radius at a 45° bend angle.

Fiber-reinforced Aerogel composite insulations provide superior thermal insulation protection in both the low-earth orbit (LEO) and near-earth neighborhood planetary environments. The flexible nature and thermal properties of these materials make them the best insulation candidates for advanced space suit application. This paper reviews the properties of various Aerogel composite materials developed for NASA by Aspen Systems, Inc. Previous studies showed that the Aerogel materials retained acceptable thermal performance after some amount of mechanical cycling. The goal of the current work is to reach a complete understanding of the mechanical properties of these materials in the domain of space suit application. Hence, a good knowledge of the durability of the aerogel composites is needed. This paper presents the extensive testing program needed to determine the life of these insulations for advanced space suit application.

For planetary exploration, new thermal insulation materials are needed to deal with unique environmental conditions presented to extravehicular activity (EVA). The thermal insulation material and system used in the existing space suit were specifically designed for low orbit environment. They are not adequate for low vacuum condition commonly found in planetary environments with a gas atmosphere. This study attempts to identify the types of lofty nonwoven thermal insulation materials and the construction parameters that yield the best performance for such application. Lofty nonwovens with different construction parameters are evaluated for their thermal conductivity performance. Three different types of fiber material: solid round fiber, hollow fiber, and grooved fiber, with various denier, needling intensity, and web density were evaluated.

The effectiveness of three different techniques, designed to improve the bending fatigue life in comparison to conventionally processed gas-carburized 8620 steel, were evaluated with modified Brugger bending fatigue specimens and actual ring and pinion gears. The bending fatigue samples were machined from forged gear blanks from the same lot of material used for the pinion gear tests, and all processing of laboratory samples and gears was done together. Fatigue data were obtained on standard as-carburized parts and after three special processing histories: shot-peening to increase surface residual stresses; double heat treating to refined austenite grain size; and vacuum carburizing to minimize intergranular oxidation. Standard room-temperature S-N curves and endurance limits were obtained with the laboratory samples. The pinions were run as part of a complete gear set on a laboratory dynamometer and data were obtained at two imposed torque levels.

Crack initiation and propagation in an SAE 4320 steel gas carburized to a 1.0 mm case depth was examined in specimens subjected to bending fatigue. Cellulose acetate replicas of incrementally loaded specimens showed that small, intergranular cracks were initiated during static loading to stress levels just above the endurance limit. The intergranular cracks arrest and serve as initiation sites for semi-elliptical, transgranular fatigue crack propagation. The maximum depth of stable crack propagation was between 0.17 and 0.23 mm, a depth which corresponds to the maximum hardness of the carburized case. Three equations which provide approximations to the stress distribution in the fatigue specimens were used to calculate KIC for the carburized case with values of maximum applied stress and measured stable crack geometry.

Quenching & Partitioning (Q&P) is receiving increased attention as a novel Advanced High Strength Steel (AHSS) processing route as promising tensile properties of the “third generation” have been reported. The current contribution reports hole expansion ratios (HER) of Q&P steels and compares the values with HERs obtained for “conventional” AHSS processing routes such as austempering and Quench & Tempering (Q&T). Intercritically annealed C-Mn-Al-Si-P and fully austenitized C-Mn-Si microstructures were studied. Optimum combinations of tensile strength and HER were obtained for fully austenitized C-Mn-Si Q&P samples. Higher HER values were obtained for Q&P than for Q&T steels for similar tempering/partitioning temperatures. Austempering following intercritical annealing results in higher HER than Q&P at similar tensile strength levels. In contrast, Q&P following full austenitization results in higher hole expansion than austempering even at higher strength levels.

In order to provide effective cooling for astronauts during extravehicular activities (EVAs), a liquid cooling and ventilation garment (LCVG) is used to remove heat by a series of tubes through which cooling water is circulated. To better predict the effectiveness of the LCVG and determine possible modifications to improve performance, computer simulations dealing with the interaction of the cooling garment with the human body have been run using the Wissler Human Thermal Model. Simulations have been conducted to predict the heat removal rate for various liquid cooled garment configurations. The current LCVG uses 48 cooling tubes woven into a fabric with cooling water flowing through the tubes. The purpose of the current project is to decrease the overall weight of the LCVG system. In order to achieve this weight reduction, advances in the garment heat removal rates need to be obtained.

This paper describes the effort and accomplishments for developing flexible fabrics with high thermal conductivity (FFHTC) for spacesuits to improve thermal performance, lower weight and reduce complexity. Commercial and additional space exploration applications that require substantial performance enhancements in removal and transport of heat away from equipment as well as from the human body can benefit from this technology. Improvements in thermal conductivity were achieved through the use of modified polymers containing thermally conductive additives. The objective of the FFHTC effort is to significantly improve the thermal conductivity of the liquid cooled ventilation garment by improving the thermal conductivity of the subcomponents (i.e., fabric and plastic tubes).

The challenges of missions to the Moon and Mars presents NASA with the need for more advanced life support systems, including better technologies for CO2 removal in spacecraft atmospheres and extravehicular mobility units (EMU). Amine-coated single wall carbon nanotubes (SWCNT) have been proposed as a potential solution because of their high surface area and thermal conductivity. Initial research demonstrated the need for functionalization of SWCNT to obtain optimal adherence of the amine to the SWCNT support phase [1]. Recent efforts focus on the development of new methods to chemically bond amines to SWCNT. Synthesis and characterization methods for these materials are discussed and some preliminary materials characterization data are presented. The CO2 adsorption capacity for several versions of SWCNT supported amine-based CO2 scrubber materials is also determined.

The quest for higher efficiency and performance of automotive vehicles requires application of materials with high strength, stiffness and lower weight in their construction. Particulate-reinforced aluminum-matrix composites are cost-competitive materials, which can meet these requirements. MMCC, Inc. has been optimizing particulate-reinforced alloy systems and developing the Advanced Pressure Infiltration Casting (APIC™) process for the manufacture of components from these materials. This paper discusses the results of a recent study in which composites reinforced with 55 vol.% alumina were cast using two sizes of alumina particulate and eight different matrix alloys based on Al-4.5 wt.% Cu with varying amounts of silicon and magnesium. Optimum heat treatments for each alloy were determined utilizing microhardness studies. The tensile strength and fracture toughness were evaluated as a function of alloy chemistry, particulate size, and heat treatment.