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The shock and spall behavior of tempered AF9628, an ultra-high strength (UHSS) martensitic low-alloy carbon steel, is investigated using gun-driven, symmetric, planar impacts. The study utilized laser velocimetry to obtain transmitted wave velocity histories that were analyzed to obtain the Hugoniot Elastic Limit (HEL), the shock Hugoniot, and the spall strength. The work was limited to the stress range below 13 GPa (below the e phase transition), and an HEL of 2.35 GPa and a spall strength of 6.8 GPa are reported. The HEL and spall strength of AF9628 are both above the typical values for inexpensive low-alloy steels, and only slightly below those for a much more expensive Aermet steel. The dynamic compressive yield strength (as calculated from the HEL) is only slightly higher than the quasi-static compressive yield strength when compared using a similar yield assignment convention, indicating a small, but positive, value of strain-rate sensitivity. The Hugoniot for AF9628, US = 0.67uP + 5.01 km/s, is in good agreement with other low-alloy martensitic steels for which data is available, and distinctly different than the Hugoniot for ferritic steels. The Hugoniot extrapolates to a bulk sound speed significantly higher than what is measured at ambient conditions, an incongruity that is unusual among metals and that the authors attribute to the unsteady nature of the shock waves generated in this work. Finally, it is suggested that there may be a relationship between dynamic compressive yield strength (calculated from the HEL) and dynamic tensile failure strength (the spall strength).

The predicted flow behaviors of Aermet 100 steel were analyzed within a wide range of temperatures of 1,073 K–1,473 K and strain rates of 0.01 s–1–50 s–1 based on isothermal compression tests. Using the original Johnson Cook (JC) model and a modified Johnson Cook (MJC) model, the constitutive equations were constructed in the case of elevated temperatures. For both the JC and MJC, and the previously studied (Arrhenius-type model and double-multivariate nonlinear regression (DMNR)) models, their respective predictability levels were evaluated by contrasting both the correlation coefficient R and the average absolute relative error (AARE). The results showed that the prediction from the three models meet the accuracy requirement based on the experimental data, the only exception being the JC model. By comparing the predictability and numbers of material constants involved, the modified Johnson Cook model is regarded as an excellent choice for predicting the flow behaviors of Aermet 100 steel within the range being studied.

In environmental impact assessment of coal plant, it is essential to determine the radius impact. This information can be used to determine the impacted area, which will significantly receive the pollution emitted from the stack for years. In this study, we use the American Meteorological Society - Environmental Protection Agency Regulatory Model (AERMOD) model, which is a regulated model in the USA and other countries. Five years hourly meteorological data for feeding AERMET model was obtained from MM5 re-analysis data. Terrain data was extracted from the SRTM30 satellite image and converted into DEM. The parameter to be considered in this study is Sulfur Dioxide (SO2), Nitrogen Dioxide (NO2), and Total Suspended Particle (TSP). The calculation shows that the pollutions tend to disperse in the south direction by the wind direction. NO2 is more disperse than SO2 and TSP. Calculation of impact radius indicates that concentration of all pollutants in annual average is below the national standard. For the case of the highest one hour average gives the radius impact of 18 km for NO2 and 9 km for SO2. For the case of the highest 24 hours, only NO2 gives value beyond the standard with an impact radius of 4.5 km. Calculation of TSP indicates that concentration is below the standard in all cases. The maximum concentration of all pollutants is detected 3 km south of the stack.

The microstructure and mechanical properties of ultrahigh strength Aermet 100 steel tempered at five different temperatures in the 472–492 °C range have been studied. The results show that the mechanical properties of Aermet 100 steel are sensitive to the tempering temperature; especially at the temperature of 482 °C, in which significant changes can be observed. At 482 °C, the strength of Aermet 100 steel sharply decreases by 70–100 MPa when the tempering temperature increases by only 5 °C. This is mainly due to the growth of M2C carbide at relatively high tempering temperature that can greatly decrease its interface strengthening effect. In addition to strength, the plasticity and fracture toughness of Aermet 100 steel obviously increase at 482 °C when compared with lower tempering temperatures. The rising amplitudes of elongation and fracture toughness can reach 1.7% and 30 MPa m1/2 respectively. This is attributed to the reverted austenite film precipitated at 482 °C. For one respect, the existence of austenite film between lath martensite can reduce the local stress concentration and the chance of microcrack formation in Aermet 100 steel during deformation, which is responsible for the obvious increase of plasticity. For another respect, the excellent softness, toughness and stability of reverted austenite prompt the advancing crack to divert, branch and blunt or appear “zigzag” route, which results in an increase in the fracture toughness. Aermet 100 steel can achieve the optimum combination of strength, plasticity and toughness at the tempering temperature of 482 °C, which has the yield strength of 1845 MPa, the elongation of 12.9% and the fracture toughness of 113 MPa m1/2.

Isothermal compression tests were conducted on A100 steel using a Gleeble 1500 thermal simulator at a temperature range of 900–1,200°C and strain rate range of 0.001–3 s−1. Results show that the A100 steel has higher strength than the Aermet 100 steel at high temperatures. Constant values, such as A, α, and n, and activate energy Q were obtained through the regression processing of the stress–strain data curves under different strains. A set of constitutive equations for A100 steel was proposed by using an Arrhenius-type equation. The optimum processing craft ranges for A100 steel based on the analysis of the hot working diagram and deformation mechanism are as follows: temperature range of 1,000–1,100°C and strain rate range of 0.01–0.1 s−1. The average grain size within this working range is 7–22.5 μm.

Climate is defined as the statistics of weather over a long period of time. Climate has a dynamic structure, and climate change is caused either by natural or anthropogenic effects. Meteorological parameters are routinely recorded by national weather stations. In this study, climate variability was analyzed in a mid-populated city in the middle of the Anatolian Peninsula. Humidity, temperature, precipitation, open surface evaporation, and solar radiation records over 57-year period from 1960 to 2016 were considered. The increase in temperature and solar radiation was obvious. The increase rates were 0.05 °C and 0.62 W/m2 for temperature and solar radiation, respectively. Relative humidity showed a declining trend from 64 to 53%. This study also aimed to evaluate the climate change of planetary boundary layer development, which influences air quality level. AERMET, which is the AERMOD meteorological preprocessor was exploited in order to simulate the planetary boundary layer height, and twice daily upper air soundings, wind speed, wind direction, ambient temperature, and cloud cover have been used as minimum required parameters. The complete meteorological data available were between 2006 and 2016; for that reason, the boundary layer was calculated for 11 years. The determined average boundary layer height was 1018 m in 2006 and was reduced to 889 m in 2016. © 2019, Springer Nature B.V., The authors greatly acknowledge Turkish State Meteorological Service for providing the extensive data set of Aksaray weather records.

Bu çalışma, özellikle kış mevsimlerinde yoğun hava kirliliğinin yaşandığı Balıkesir ili için yapılmış ilk hava kalitesi modelleme çalışmasıdır. Balıkesir il merkezinde bulunan bir sanayi işletmesinden atmosferik karbonmonoksit (CO) salınımlarının kent merkezine olan olası etkileri mevcut meteorolojik ve yüzey topoğrafya özellikleri dikkate alınarak incelenmiş ve CO salınımlarına ait yeryüzü konsantrasyonlarının dağılımlarını gösteren haritalar AERMOD ile oluşturulmuştur. Elde edilen sonuçlara göre, Balıkesir ili için uzun yıllık hakim rüzgar yönü Kuzey (N) ve Kuzey-Doğu (NE) yönlü olarak belirlenmiştir ve kaynaktan yayılan maksimum günlük 8 saatlik ortalama CO konsantrasyonu modelleme sonucuna göre 34,01 μg.m-3 olarak tahmin edilmektedir. Bu nedenle, tahmin edilen CO seviyelerinin yasal sınırları aşmadığı ve şehir merkezine olumsuz bir etkisinin olmadığı belirlenmiştir. Ayrıca incelenen kaynağa yakın kabul edilebilecek yerde tam teşekküllü bir hastanenin olması, yapılan çalışmayı daha önemli bir hale getirmektedir. Modelleme sonucuna göre, kaynaktan salınan maksimum günlük 8 saatlik ortalama CO konsantrasyonu yaklaşık 10 μg.m-3 olarak tahmin edilmiş olup, bu değerin yine aynı yönetmelikte izin verilen yasal sınırları aşmadığı tespit edilmiştir. Çalışma sonuçlarının, halkın bilinçlendirilmesine katkı sağlanması ve yerel otoriteye karar alma sürecinde öneriler sunulması da ayrıca çalışma kapsamında önem arz etmektedir. This study is the first air quality modeling study for downtown Balikesir where intense air pollution levels are experienced during the winter seasons. The possible effects of atmospheric carbonmonoxide (CO) emissions from an industrial operation in downtown Balikesir were examined by taking into consideration the existing meteorological and surface topography characteristics and the maps showing the distributions of the ground level concentrations for CO releases were created by using the AERMOD.According to the results, the prevailing wind direction was determined as North (N) and North-East (NE) for Balikesir province, and the maximum daily 8-hour means of CO concentration emitted from the source was estimated as 34,01 μg.m-3 for the modeling study. For this reason, it has been determined that the modeled CO concentrations do not exceed the legal limits and there is no adverse effect on the downtown area. In addition, the fact that, there was a full-scaled hospital that was located nearby the source. The location of hospital complex made the air quality modeling study more significant. According to the modeling result, the maximum daily 8-hour means of CO concentration released from the source was estimated to be about 10 μg.m-3 for the hospital area. It has also been determined that the modeled value for hospital does not exceed the legal limits as states in the regulation. Within the scope of the study, the obtained results are also important due to contribution to raising public awareness and also provide suggestions to local authority in decision-making process.

Some upper air atmospheric parameters measured during period of 2011-2016 by means of radiosonde located at Hasanuddin International Airport were examined for characterization of boundary layer over Makassar, Indonesia. These data, combined with surface atmospheric parameters were used to calculate some boundary layer parameters using AERMET model which based on Monin-Obukhov similarity theory. The obtained Monin-Obukhov length which reflecting atmospheric stability then converted into traditional Pasquill-Gifford stability classification. Examination of wind characteristics of wind showing clearly their dependence of the day, season and height. Winds dominantly flows from the southeast during the daytime with the relatively larger velocity and from the northwest with smaller velocity during the nighttime. Interpretation of monin-obukhov length using Pasquill-Gifford stability classification showing that the atmosphere was dominantly unstable during the daytime and dominantly stable during the nighttime. These atmospheric stabilities were also varied during seasons. The height of convective boundary layer (CBL) was start to rise in the morning and reaching its maximum in the afternoon (18:00) at the mean value of 2 km. Meanwhile, the height of mechanical boundary layer (MBL) during the day time forming parabolic curve with its maximum value of 1.2 km at noon. These indicated that any released pollution from the stack will be less dispersed during the nighttime due to the fact of lower mixing height, lower wind speed, atmosphere become more stable, and it dispersed in different direction compare to the daytime.

This study compares MM5 and WRF modeled upper air and surface wind speed and direction with observations from two standard meteorological stations locat;ed in areas characterized by either flat or complex terrain. Additionally, we evaluate the boundary layer height calculated by AERMET VIEW Upper Estimator. The upper air wind speed predictions of MM5 (but not of WRF) met all the acceptance criteria. In contrast, WRF surface wind predictions were mostly in better agreement with the observations than those of MM5, with a clear advantage for the 12 km grid resolution over the 3 km grid resolution. Modeled wind fields over complex terrain were less accurate than over flat terrain. Based on these results we conclude that in the absence of measured on-site meteorological data, WRF surface wind field predictions are expected to provide more reliable pollutant dispersion estimations and to propagate the estimation uncertainties to a lesser extent than MM5 surface wind field predictions, in particular for flat terrain scenarios.

AerMet 100 exhibits excellent mechanical properties with both high yield strength and excellent ductility. Understanding the dynamic mechanical behavior of the material should clear the road for wider application of AerMet 100 as critical mechanical parts serving in extreme mechanical conditions. In this paper, the strain rate dependency of AerMet 100 is investigated by using Split-Hopkinson pressure bar (SHPB) and also compared with its quasi-static counterpart. Based on the experiment results, a simplified Johnson–Cook model is established to describe the strain rate dependent behaviors and is proved to perform better than Cowper–Symonds model. The validation of the suggested constitutive model is embedded in the finite element analysis and can well repeat the strain wave observed from experiment results. Furthermore, the impact fracture toughness of AerMet 100 is also studied both numerically and experimentally. Finally, a thin-walled tube made of AerMet 100 is numerically simulated and the excellent crashworthiness is proven. Results may enlighten the understanding of dynamic mechanical behavior of AerMet 100 and provide fundamental experiment data for its future engineering applications. Keywords: AerMet 100, Strain rate effect, Constitutive behavior, SHPB method, Numerical simulation

In this paper, we present a numerical model to study pollutant dispersion in the atmospheric boundary layer (ABL). The model accounts for the mechanisms of advection by the mean wind in the horizontal direction, turbulent diffusion in the vertical direction to ground surface, dry deposition, and radioactive decay. More importantly, the model is capable of accounting for the evolution of the ABL structure over a diurnal cycle by considering parameterizations for the wind-speed and eddy-diffusivity profiles that depend on the atmospheric stability condition, which in turn undergoes dramatic changes throughout the day. To solve the resulting advection–diffusion equation, we propose a numerical method based on a stabilized finite element formulation. After validating the numerical model by simulating classical experiments and comparing its predictions with those available in literature, we study the dispersion of a pollutant during a full diurnal ABL cycle with the meteorological parameters generated by AERMET for a 24-h period on a 1-h basis.

Air quality in most parts of Kay County is good and unlikely to cause major health problems. However, Kaw Nation wants to know if the concentration of Particulate matters (PM2.5) and Sulfur dioxide (SO2) released from power plants, refinery and carbon black plant in Oklahoma reaches the Tribal land at Kanza Travel Plaza, Braman, Kay Co. Oklahoma. Kanza Travel Plaza is located in the north central Oklahoma 22 miles Northwest of Ponca City at a latitude of 36.9395 degrees North and longitude of -97.3453 degrees West. In order to estimate the concentration of PM2.5 and SO2 that reaches the Tribal land, Kaw Nation run the U.S. Environmental Protection Agency regulatory air quality model called AERMOD (Version 15181). AERMOD is a steady state plume model that measures dispersion of gases and particulate matters from the source to the point of impact within source radius. The study sites are flat and rural conditions with less complex terrain. Meteorological data representative of the study area was preprocessed using AERMET program. AERMET prepares hourly surface data and upper air data. The hourly surface data was obtained from Station #3965 (Stillwater Regional), while the upper air data was obtained from Station #3948 (Norman). The Building parameters such as height and length were processed using the building profile called BPIB. To calculate the concentration of PM2.5 and SO2 air pollutants released from the coal power plant the Gaussian air molding (AERMOD) used Control, Source, Receptor, Metrological and Output pathways. The AERMOD result indicates at least 19-26% of PM2.5 and SO2 released from the stacks of the power plants, refinery and carbon black plant into the atmosphere reaches the Tribal land. Based on the Gaussian air modeling (AERMOD and BAM 1020 Continuous Air monitor) less than 12 µg/m3 of pollutant has been captured that falls within the attainment zone as per the National Ambient Air Quality Standards (NAAQS).

Distributed power generation, located close to consumers, plays an important role in the current and future power systems. However, its near-source impacts in complex urban environments are not well understood. In this paper, we focused on diesel backup generators that participate in demand response (DR) programs. We first improved the micro-environmental air quality simulations by employing a meteorology processor, AERMET, to generate site-specific boundary layer parameters for the Large Eddy Simulation (LES) modeling. The modeling structure was then incorporated into the CTAG model to evaluate the environmental impacts of diesel backup generators in near-source microenvironments. We found that the presence of either tall upwind or downwind building can deteriorate the air quality in the near-stack street canyons, largely due to the recirculation zones generated by the tall buildings, reducing the near-stack dispersion. Decreasing exhaust momentum ratio (stack exit velocity/ambient wind velocity) draws more exhaust into the recirculation zone, and reduces the effective stack height, which results in elevated near-ground concentrations inside downwind street canyons. The near-ground PM2.5 concentration for the worst scenarios could well exceed 100 μg m−3, posing potential health risk to people living and working nearby. In general, older diesel backup generators (i.e., Tier 1, 2 or older) without the up-to-date emission control may significantly increase the pollutant concentration in the near-source street canyons if participating in DR programs. Even generators that comply with Tier-4 standards could lead to PM hotspots if their stacks are next to tall buildings. Our study implies that the siting of diesel backup generators stacks should consider not only the interactions of fresh air intake and exhaust outlet for the building housing the backup generators, but also the dispersion of exhaust plumes in the surrounding environment.

The present work is part of the research project that aims to create an automated system for the evaluation of air pollution and odour for CMPC CELULOSE RIOGRANDENSE. Initially, three different ways of initializing the CALPUFF model (one of the models under evaluation to compose the system) were evaluated. The results when compared with observational data on air quality suggest the need for a validation of the boundary conditions and turbulent scale parameters in the hourly time representation when CALPUFF is the model being used. The choice was not random, but based on three quantities that impose physical affinity to micrometeorological data. The surface roughness, the albedo and the Bowen ratio. Changes in these quantities were imposed during pre-processing of AERMET, which established the quantities of interest in a simulation of dispersion of pollutants. After this alternative the results become more representative for the atmospheric dispersion process. The monthly and annual representation of the CALPUFF model is satisfactory without validation procedure.

In this research we aim to present a fast and semi-quantitative electrochemical method – based on cyclic voltammetry (CV) – to easily screen the H uptake of materials. We used Aermet 100, an ultrahigh-strength steel, in its as-quenched (martensitic) state and an aged state to investigate the H-desorption properties of different microstructures. The CV-based method clearly shows the influence of the alloying elements, the microstructure and the effect of hydrogen recombination poisons on the H uptake. The experiments indicate that a significant part of the uptake of hydrogen is due to (i) the presence of Ni as an alloying element and (ii) the presence of austenite that forms during the heat treatment.

This paper investigates grinding force and grinding temperature of ultra-high strength steel Aermet 100 in conventional surface grinding using a single alumina wheel, a white alumina wheel and a cubic boron nitride wheel. First, mathematical models of grinding force and grinding temperature for three wheels were established. Then, the role of chip formation force and friction force in grinding force was investigated and thermal distribution in contact zone between workpiece and wheel was analyzed based on the mathematical model. The experimental result indicated that the minimum grinding force and the maximum grinding force ratio under the same grinding parameters can be achieved when using a CBN wheel and a single alumina wheel, respectively. When the phenomenon of large grinding force and high grinding temperature appeared, the workpiece material would adhere locally to the single alumina wheel. Grinding temperature was in a high state under the effect of two main aspects: poor thermal properties of grinding wheel and low coolant efficiency. The predicted value of grinding force and grinding temperature were compared with those experimentally obtained and the results show a reasonable agreement.

The stress corrosion crack (SCC) susceptibility of ultra-high strength steel AerMet 100 was investigated by slow strain rate technique (SSRT), tensile with polarization and surface analysis technique. The curves of tfCl/tfW-strain rate are divided into three regions: stress-dominated region, SCC-dominated region, and corrosion-dominated region, so as the curves of ɛfCl/ɛfW-strain rate and tm/tf-strain rate. The results of tensile tests with polarization show that the main SCC mechanism of AerMet 100 is anodic dissolution, which controls the corrosion process. The three regions have been discussed according to the relationship between the rate of slip-step formation and the rate of dissolution. Fracture appearances in different environments were analyzed by scanning electron microscopy (SEM). SCC fracture appears as a mixture of intergranular and dimples, while it is totally dimples in the inert environment. The ɛf becomes the parameter to predict tf because the relationship between ɛfCl/ɛfW and tfCl/tfW is a straight line for AerMet 100.

Monitoring campaigns from different locations have recently shown how air concentrations of persistent semivolatile contaminants such as polychlorinated biphenyls (PCBs) often exhibit short-term (less than 24 h) variations. The observed patterns have been ascribed to different factors, such as temperature-mediated air-surface exchange and variability of planetary boundary layer (PBL) height and dynamics. Here, we present a new modeling approach developed in order to investigate the short-term variability in air concentrations of organic pollutants at a local scale. A new dynamic multimedia box model is supplied by a meteorological preprocessor (AERMET) with hourly values of air compartment height and wind speed. The resulting model is tested against an existing dataset of PCB air concentrations measured in Zurich, Switzerland. Results show the importance of such modeling approach in elucidating the short- and long-term behavior of semivolatile contaminants in the air/soil system.

This paper describes the methodology used to incorporate two numerical plume rise algorithms, one by Janicke and Janicke and another by Webster and Thomson, into the Lagrangian particle model LAPMOD. LAPMOD is fully interfaced with the diagnostic meteorological model CALMET, which is part of the widely used CALPUFF modeling system. LAPMOD can also use the meteorological input files produced with the AERMET meteorological processor of the US-EPA recommended model AERMOD. This paper outlines the theory behind the two plume rise algorithms and the details of their implementation in LAPMOD. The paper also provides the results of the evaluation of LAPMOD and its included plume rise algorithms against the well-known Indianapolis and Kincaid SF6 and SO2 field studies and tracer experiments. The performance of LAPMOD is successfully evaluated with the Model Evaluation Kit and compared with that of other air quality models.

Fluid catalytic cracking unit is of great importance in petroleum refining industries as it treats heavy fractions from various process units to produce light ends (valuable products). FCC unit feedstock consists of heavy hydrocarbon with high sulfur contents, and the catalyst in use is zeolite impregnated with rare earth metals, i.e., lanthanum and cerium. Catalytic cracking reaction takes place at elevated temperature in fluidized bed reactor generating sulfur-contaminated coke on the catalyst with large quantity of attrited catalyst fines. In the regenerator, coke is completely burnt producing SO2, PM emissions. The impact of the FCC unit is assessed in the immediate neighborhood of the refinery. Year-long emission inventories for both SO2 and PM have been prepared for one of the major petroleum refining industry in Kuwait. The corresponding comprehensive meteorological data are obtained and preprocessed using Aermet (Aermod preprocessor). US EPA approved dispersion model, Aermod, is used to predict ground level concentrations of both pollutants in the selected study area. Model output is validated with measured values at discrete receptors, and an extensive parametric study has been conducted using three scenarios, stack diameter, stack height, and emission rate. It is noticed that stack diameter has no effect on ground level concentration, as stack exit velocity is a function of stack diameter. With the increase in stack height, the predicted concentrations decrease showing an inverse relation. The influence of the emission rate is linearly related to the computed ground level concentrations.

Some common high strength steels possess enough magnetostriction to serve as the active material in sensors, e.g. torque sensors, while simultaneously performing their usual structural role. The magnetization and magnetostriction of six common high strength steels have been measured as a function of stress. Measurements were made in a hydraulic load frame at compressive stresses of -1, -50, -100, and -150 MPa with fields up to 135 kA/m (1700 Oe). With two exceptions, all of the samples displayed ldquonormalrdquo strain-field curves. The exceptions were Maraging 300 steel whose magnetostriction was continuing to increase with stress even at -150 MPa and an SAE 4130 steel that showed an ldquoinverted V rdquo shape. B-H curves of all of the samples showed some small dependencies on stress but were otherwise unremarkable. The saturation magnetostrictions (muS = 1 times 10-6) and saturation magnetization (tesla) were: AerMet 100 [30 muS, 1.68 T]; HP 9-4-20 [23 muS, 1.68 T]; SAE 4130 [10 muS, 1.81 T]; Maraging 300 [32 muS (at -150 MPa), 1.67 T]; SAE 4340 [5 muS, 1.58 T]; SAE 9310 (heat treatment I) [10 muS, 1.77 T]; and SAE 9310 (heat treatment II) [12 muS, 1.82 T]. Details of the heat treatments are given.

The present study examines the strain-rate sensitivity of four high-strength, high-toughness steels at strain-rates ranging from 0.0002 s −1 to 200 s −1 : AerMet 100, modified 4340, modified HP9-4-20, and a recently developed Eglin AFB steel alloy, ES-1c. A newly developed dynamic servohydraulic method was employed to perform tensile tests over this entire range from quasi-static to near split-Hopkinson or Kolsky bar strain-rates. Each of these alloys exhibits only modest strain-rate sensitivity. Specifically, the semi-logarithmic strain-rate sensitivity factor β was found to be in the range of 14–20 MPa depending on the alloy. This corresponds to a ∼10% increase in the yield strength over the 6-orders of magnitude change in strain-rate. Interestingly, while three of the alloys showed a concomitant ∼3–10% drop in their ductility with increasing strain-rate, the ES-1c alloy actually exhibited a 25% increase in ductility with increasing strain-rate. Fractography suggests the possibility that at higher strain-rates ES-1c evolves towards a more ductile dimple fracture mode associated with microvoid coalescence.

Cylinders and rings fabricated from AerMet ® 100 alloy and AISI 1018 steel have been explosively driven to fragmentation in order to determine the fracture strains for these materials under plane-strain and uniaxial-stress conditions. The phenomena associated with the dynamic expansion and subsequent break up of the cylinders are monitored with high-speed diagnostics. In addition, complementary experiments are performed in which fragments from the explosively driven cylinders are recovered and analyzed to determine the statistical distribution associated with the fragmentation process as well as to determine failure mechanisms. The data are used to determine relevant coefficients for the Hancock–McKenzie (Johnson–Cook) fracture model. Metallurgical analysis of the fragments provides information on damage and failure mechanisms.

Microstructural variation across inertia friction welded Aermet 100 (ultra-high strength secondary hardening steel) and SCMV (high strength low alloy Cr–Mo steel) has been studied. Retained austenite was mapped in two dimensions across the inertia friction welds using synchrotron-X ray diffraction. Microhardness testing and SEM were used to characterize the general microstructure variation across the weld line in the as-welded and post-weld-heat-treated (PWHT) conditions. Four distinct microstructural zones were observed for the as-welded condition in the heat-affected zone. Subsequent PWHT resulted in a reduction of the peak hardness on adjacent sides of the weld with all other areas increasing in hardness. These changes in hardness are explained based on tempering of the martensitic structure and precipitation reactions during PWHT.

Constant strain rate, constant velocity and Hopkinson Pressure Bar compression tests were carried out on AerMet 100 martensitic steel between 1130 °C and 1250 °C spanning strain rates from 0.01 s−1 to 4000 s−1. The results were used to generate a predictive flow stress model over the entire range of test conditions. The effect of initial austenite grain size on flow stress was found to follow the Hall–Petch relationship. This dependency was then removed through innovative heat treatments. The morphology of the flow stress curves were also dependent on mechanisms of microstructural evolution which were controlled by the test method, strain rate and temperature. Friction and adiabatic heating also had a major contribution. A novel method was proposed in order to define the flow stress, which was then used to determine the work hardening exponent of the Zener–Hollomon equation. It was found that a deviation from the linear trend was observed in Hopkinson Pressure Bar tests and reasons were given. An artificial neural network approach was used to determine a more accurate predictive flow stress model which included the effects of test method, temperature, stain rate and initial austenite grain size. The method showed that it was possible to predict the flow stress between 50 and 2000 s−1 where mechanical testing’s results were absent.

The diffusivity of hydrogen at room temperature in an ultra high strength steel Aermet® 100 was studied using a variety of techniques, such as an electrochemical method, sub-surface microhardness profiling, quantitative depth profiling using nuclear reaction analysis (NRA) and nanohardness profiling. Aermet® 100 samples were cathodically charged under a galvanostatic condition at a current density of 10 A/m2. The electrochemical technique was used to determine the diffusivity of hydrogen in the Aermet® 100 cathode by monitoring the potential as a function of time. These results were compared with diffusivity data extracted from sub-surface microhardness profiling. Independently, nanohardness depth profiling was carried out to validate the hardness data near the surface. Excellent correlations were obtained in the data for hydrogen diffusivity from each of these techniques. The room temperature hydrogen diffusivity in Aermet® 100 was measured at approximately 2.91×10−13 m2/s. NRA indicated that the near-surface concentration of hydrogen under the electrolytic charging conditions utilized was about 5 at.%.

The purpose of this study is to report well-controlled experiments conducted to determine the fracture resistant properties of AerMet® 100 steels. One of the objectives of this study is to determine the influence of fracture toughness properties on the fracture and fragmentation process. Both sphere impact tests and cylinder expansion test geometry were used to determine the dynamic fracture resistant coefficients. These experiments were conducted at strain rates of ∼ 14 × 10 3 /s for the cylinder expansion tests; the strain rates for the sphere impact tests varied over 50 to 100 × 10 3 /s. Fracture resistant coefficients of 60 MPa √m and 20 MPa √m are obtained from the cylinder test and the sphere impact test, respectively. These measurements do not agree with the static fracture toughness values reported in the literature.

Non-proportional torsion–tension and biaxial-compressive experimental results are presented on tantalum, tantalum alloy with 2.5% tungsten, and AerMet 100 steel. These test results form a comprehensive set of data to show the material behaviors at finite strain and wide strain-rate range. Using the parameter set determined from uniaxial constant strain-rate compressive and tensile tests, the capability of a new constitutive model (Khan, A.S., Liang, R., 1999. Behaviors of three BCC metal over a wide range of strain rates and temperatures: experiments and modeling. International Journal of Plasticity 15, 1089–1109) is shown to accurately predict complex loading paths of current experimental results. Using von Mises equivalent strain, stress, and strain rate, the constitutive model gives excellent predictions of these non-proportional experimental results.

Summary We performed a series of depth-of-penetration experiments using 7.11-mm-diameter, 71.12-mm-long, ogive-nose steel projectiles and 254-mm-diameter, 6061-T6511 aluminum targets. The projectiles were made from vacuum-arc remelted (VAR) 4340 steel (Rc 38) and AerMet 100 steel (Rc 53), had a nominal mass of 0.021 kg, and were launched using a powder gun or a two-stage, light gas gun to striking velocities between 0.5 and 3.0 km/s. Since the tensile yield strength of AerMet 100 (Rc 53) steel is about 1.5 times greater than VAR 4340 (Rc 38) steel, we were able to demonstrate the effect of projectile strength on ballistic performance. Post-test radiographs of the targets showed three different regions of penetrator response as the striking velocity increased: (1) the projectiles remained rigid and visibly undeformed; (2) the projectiles deformed during penetration without nose erosion, deviated from the target centerline, and exited the side of the target or turned severely within the target; and (3) the projectiles eroded during penetration and lost mass. To show the effect of projectile strength, we present depth-of-penetration data as a function of striking velocity for both types of steel projectiles at striking velocities ranging from 0.5 and 3.0 km/s. In addition, we show good agreement between the rigid-projectile penetration data and a cavityexpansion model.

The elastic–plastic behaviors of three body-centered cubic metals, tantalum, tantalum alloy with 2.5% tungsten, and AerMet 100 steel, are presented over a wide range of strains (15%), strain rates (10−6–104 s−1) and temperatures (77–600°F). Johnson-Cook and Zerilli-Armstrong models were found inadequate to describe the observations. A new viscoplastic model is proposed based on these experimental results. The proposed constitutive model gives good correlations with these experimental results and strain-rate jump experiments. In the next paper (Liang, R., Khan A.S., 2000. Behaviors of three BCC metals during non-proportional multi-axial loadings and predictions using a recently proposed model. International Journal of Plasticity, in press), multi-axial loading results on these materials and comparison with the proposed model will be presented.

Hydrogen trapping in three high-strength steels—AerMet 100 and AISI 4340 and H11—was studied using a potentiostatic pulse technique. Irreversible trapping constants ( k ) and hydrogen entry fluxes were determined for these alloys in 1 mol/l acetic acid/1 mol/l sodium acetate. The order of the k values for the three steels and two 18Ni maraging steels previously studied inversely parallels their threshold stress intensities for stress corrosion cracking ( K ISCC ). Irreversible trapping in AerMet 100 varies with aging temperature and appears to depend on the type of carbide (Fe 3 C or M 2 C) present. For 4340 steel, k can be correlated with K ISCC over a range of yield strengths. The change in k is consistent with a change in the principal type of irreversible trap from matrix boundaries to incoherent Fe 3 C. The principal irreversible traps in H11 at high yield strengths are thought to be similar to those in 4340 steel.

We conducted depth of penetration experiments in concrete targets with 3.0 caliber-radius-head, steel rod projectiles. The concrete targets with 9.5 mm diameter limestone aggregate had a nominal unconfined compressive strength of 58.4 MPa (8.5 ksi) and density 2320 kg/m3. To explore geometric projectile scales, we conducted two sets of experiments. Projectiles with length-to-diameter ratio of ten were machined from 4340Rc 45 steel, round stock and had diameters and masses of 20.3 mm, 0.478 kg and 30.5 mm, 1.62 kg. Powder guns launched the projectiles to striking velocities between 400 and 1200 m/s. For these experiments, penetration depth increased as striking velocity increased. When depth of penetration data was divided by a length scale determined from our model, the data collapsed on a single curve. Thus, a single dimensionless penetration depth versus striking velocity prediction was in good agreement with the data at two geometric projectile scales for striking velocities between 400 and 1200 m/s. In addition, we conducted experiments with AerMet 100Rc 53 steel projectiles and compared depth of penetration and post-test nose erosion data with results from the 4340Rc 45 steel projectiles.

Fracture mechanics tests were carried out for AerMet 100 in distilled water and NaCl (3.5 and 35 gl−1). The initiation period at higher values of the stress intensity factor indicated that load application in the stress corrosion cracking (SCC) environment is a necessary but not sufficient factor for SCC and that time is needed for some other factor (e.g., the local hydrogen concentration) to reach an appropriate value. The threshold stress intensity factor, KISSC, was found to increase with decreasing NaCl concentration. The plateau stress corrosion crack velocity was 2 × 10−8 m s−1 for NaCl (3.5 and 35 gl−1). The fracture mode was transgranular with small areas of an intergranular nature.

Inertia friction welding is the process in which stored kinetic energy in a flywheel is converted to heat by relative sliding movement between the components’ surfaces. The process is widely used in joining high strength aero-engine alloys. Heat transfer interactions play a fundamental role in determining weld quality as temperature has a significant impact on the mechanical, thermal and metallurgical behaviours of materials. Heating and cooling rates influence thermal stresses induced by variations in material properties due to variations in temperatures. Heat transfer modes involved in the IFW process, apart from conduction, were hardly mentioned in previous work while their significance has not been identified. In this paper the heat transfer modes and their significance in the modelling of the IFW process of the high strength steels SCMV and AerMet 100 has been identified and a methodology by which experimental, numerical and empirical approaches were collectively utilised to optimize the heat transfer analysis is presented. The methodology was validated for optimizing the heat transfer analysis of the IFW process of the high strength steels that are the subject of this study.

The present study examines the strain-rate sensitivity of four high strength, high-toughness alloys at strain rates ranging from 0.0002 s-1 to 200 s-1: Aermet 100, a modified 4340, modified HP9-4-20, and a recently developed Eglin AFB steel alloy, ES-1c. A refined dynamic servohydraulic method was used to perform tensile tests over this entire range. Each of these alloys exhibit only modest strain-rate sensitivity. Specifically, the strain-rate sensitivity exponent m, is found to be in the range of 0.004-0.007 depending on the alloy. This corresponds to a {approx}10% increase in the yield strength over the 7-orders of magnitude change in strain-rate. Interestingly, while three of the alloys showed a concominant {approx}3-10% drop in their ductility with increasing strain-rate, the ES1-c alloy actually exhibited a 25% increase in ductility with increasing strain-rate. Fractography suggests the possibility that at higher strain-rates ES-1c evolves towards a more ductile dimple fracture mode associated with microvoid coalescence.

The ideal structural steel combines high strength with high fracture toughness. This dissertation discusses the toughening mechanism of the Fe/Co/Ni/Cr/Mo/C steel, AerMet 100, which has the highest toughness/strength combination among all commercial ultrahigh strength steels. The possibility of improving the toughness of this steel was examined by considering several relevant factors.

A database of mechanical properties for weldment fusion and heat-affected zones was established for AerMet{reg_sign}100 alloy, and a study of the welding metallurgy of the alloy was conducted. The properties database was developed for a matrix of weld processes (electron beam and gas-tungsten arc) welding parameters (heat inputs) and post-weld heat treatment (PWHT) conditions. In order to insure commercial utility and acceptance, the matrix was commensurate with commercial welding technology and practice. Second, the mechanical properties were correlated with fundamental understanding of microstructure and microstructural evolution in this alloy. Finally, assessments of optimal weld process/PWHT combinations for cotildent application of the alloy in probable service conditions were made. The database of weldment mechanical properties demonstrated that a wide range of properties can be obtained in welds in this alloy. In addition, it was demonstrated that acceptable welds, some with near base metal properties, could be produced from several different initial heat treatments. This capability provides a means for defining process parameters and PWHT's to achieve appropriate properties for different applications, and provides useful flexibility in design and manufacturing. The database also indicated that an important region in welds is the softened region which develops in the heat-affected zone (HAZ) and analysis within the welding metallurgy studies indicated that the development of this region is governed by a complex interaction of precipitate overaging and austenite formation. Models and experimental data were therefore developed to describe overaging and austenite formation during thermal cycling. These models and experimental data can be applied to essentially any thermal cycle, and provide a basis for predicting the evolution of microstructure and properties during thermal processing.

Machinability of Aermet 100, an ultrahigh strength alloy developed for Navy by Carpenter Technology as a candidate material for aircraft landing gear application, was studied by performing single-point turning tests. Coated and uncoated carbides, ceramic, and cermet cutting tool inserts of a square geometry (SNG 432 type) were used. Round stock workpieces were tested in the as - received, unaged condition and without using any cutting fluid. The turning tests for each tool material were conducted by (i) first establishing the cutting conditions that would allow the continued generation of broken chips during a given cutting test, (ii) measuring intermittently the flank wear as a function of cutting time under such established cutting conditions for discontinuous broken chips, and (iii) determining the tool life using the criteria specified in the ISO Standard 3685: 1993(E). Cutting tools except some uncoated carbide and ceramic were used with a mechanical chip breaker to induce chip breakage and avoid the generation of long continuous chips. The results obtained include the optimal cutting conditions for discontinuous chips, tool wear - cutting time curves, and records of tool life and tool failure mode for each tool material. From the measured tool life and cutting conditions, the amount of material removed by each cutting material was calculated. Coated carbide with CVD tri-phase coating showed the longest tool life that exceeded the twelve minute criterion and removed the highest amount of material per tool. Other tools failed by cutting edge chipping and their lives were shorter.

Several test welds were made on AerMet 100 alloy. Both electron beam and pulsed Nd:YAG laser beam welding processes were used to make the welds. All welds were satisfactory, with no cracking or porosity noted in weld cross-sections. 2 refs., 6 figs.

The dynamic properties characterization of AerMet 100 Steel at four different strain rates, namely 560/s, 1200/s, 2500/s and 4200/s were carried by a SHPB system. The stress-strain curves at these strain rates are obtained and they were compared with the quasi-static test results to analyze its strain effects. By comparing the stress-strain curves under different strain rates and quasi-static results, it can be found that the AerMet 100 shows strong strain rate sensitivity. For example, its yield stress under quasi-static compression is 1800MP while the yield stress is around 2300MP under strain rate 4200/s with an incensement of 24%. The hardening modulus under static compression is larger than that under dynamic compression due to the softening by the high temperature during high velocity impacting.