Environmental fatigue in aluminum-lithium alloys

Aluminum-lithium alloys exhibit similar environmental fatigue crack growth characteristics compared to conventional 2000 series alloys and are more resistant to environmental fatigue compared to 7000 series alloys. The superior fatigue crack growth behavior of Al-Li alloys 2090, 2091, 8090, and 8091 is due to crack closure caused by tortuous crack path morphology and crack surface corrosion products. At high R and reduced closure, chemical environment effects are pronounced resulting in accelerated near threshold da/dN. The beneficial effects of crack closure are minimized for small cracks resulting in rapid growth rates. Limited data suggest that the 'chemically small crack' effect, observed in other alloy system, is not pronounced in Al-Li alloys. Modeling of environmental fatigue in Al-Li-Cu alloys related accelerated fatigue crack growth in moist air and salt water to hydrogen embrittlement

The growth of small corrosion fatigue cracks in alloy 2024

The corrosion fatigue crack growth characteristics of small surface and corner cracks in aluminum alloy 2024 is established. The damaging effect of salt water on the early stages of small crack growth is characterized by crack initiation at constituent particle pits, intergranular microcracking for a less than 100 micrometers, and transgranular small crack growth for a micrometer. In aqueous 1 percent NaCl and at a constant anodic potential of -700 mV(sub SCE), small cracks exhibit a factor of three increase in fatigue crack growth rates compared to laboratory air. Small cracks exhibit accelerated corrosion fatigue crack growth rates at low levels of delta-K (less than 1 MPa square root of m) below long crack delta-K (sub th). When exposed to Paris regime levels of crack tip stress intensity, small corrosion fatigue cracks exhibit growth rates similar to that observed for long cracks. Results suggest that crack closure effects influence the corrosion fatigue crack growth rates of small cracks (a less than or equal to 100 micrometers). This is evidenced by similar small and long crack growth behavior at various levels of R. Contrary to the corrosion fatigue characteristics of small cracks in high strength steels, no pronounced chemical crack length effect is observed for Al by 2024 exposed to salt water

AI Robotic Arm with Hand Tracking

This project aims to build a robotic arm with artificial intelligence. Implementation methods included building a 3D-printed forearm, writing a Python program with OpenCV and MediaPipe to read the webcam footage and give the Arduino Uno a command sequence with five binary values depending on if the fingers were determined to be opened, which is the value ‘1’, or closed which is the value is \u270\u27 and writing a C++ program to read the given binary values from the Python program to cause each finger motor to close or open the finger. Although built, the webcam for the arm turns off randomly, preventing the arm from constantly taking in data. If this happens, the Python program also has to be manually run again. There are also limitations in the hand gestures it re-creates. For example, the fingers cannot cross over each other or move horizontally. The thumb must also be close to the palm rather than its natural position. The wrist also does not rotate. Current outcomes include running the system for a few minutes without a random webcam interruption. To solve the restriction of movement from each finger, a more articulated version of the hand is being designed. Overall, this abstract seeks to provide a comprehensive understanding of how to build an artificial intelligence arm with OpenCV and MediaPipe

Environmental fatigue of an Al-Li-Cu alloy. Part 1: Intrinsic crack propagation kinetics in hydrogenous environments

Deleterious environmental effects on steady-state, intrinsic fatigue crack propagation (FCP) rates (da/dN) in peak aged Al-Li-Cu alloy 2090 are established by electrical potential monitoring of short cracks with programmed constant delta K and K(sub max) loading. The da/dN are equally unaffected by vacuum, purified helium, and oxygen but are accelerated in order of decreasing effectiveness by aqueous 1 percent NaCl with anodic polarization, pure water vapor, moist air, and NaCl with cathodic polarization. While da/dN depends on delta K(sup 4.0) for the inert gases, water vapor and chloride induced multiple power-laws, and a transition growth rate 'plateau'. Environmental effects are strongest at low delta K. Crack tip damage is ascribed to hydrogen embrittlement because of the following: (1) accelerated da/dN due to part-per-million levels of H2O without condensation; (2) impeded molecular flow model predictions of the measured water vapor pressure dependence of da/dN as affected by mean crack opening; (3) the lack of an effect of film-forming O2; (4) the likelihood for crack tip hydrogen production in NaCl, and (5) the environmental and delta K-process zone volume dependencies of the microscopic cracking modes. For NaCl, growth rates decrease with decreasing loading frequency, with the addition of passivating Li2CO3, and upon cathodic polarization. These variables increase crack surface film stability to reduce hydrogen entry efficiency. The hydrogen environmental FCP resistance of 2090 is similar to other 2000 series alloys and is better than 7075

Understanding the Mechanics and Flight Controls of Drones: Challenges and Opportunities

This project aims to understand the mechanics and flight controls of drones. Implementation methods included building a Raspberry Pi drone and setting up NewBeeDrones. Understanding the design and hardware (GPS, motors, ESCs, etc.) that go into building a successful drone is important. Although built, the Raspberry Pi drone has had problems with calibrating the ESC motors. It is expected to solve this issue to be able to fly the drone outside. The project\u27s scope was changed to learning about NewBeeDrones to continue developing knowledge of drones. Current outcomes include successfully binding several drones to their radio controllers and FatShark goggles, setting up Pre-Arm, and changing VTX bands and channels. To further this project, a drone gate was built with an Arduino Uno, ultrasonic sensors, an LCD display and a LED strip. It can start a stopwatch when a drone goes past the sensors along with starting a rainbow light effect with the LEDs and stop the stopwatch when the drone is detected again, thus recording the race lap time. It can also reset the stopwatch to start a new lap time. A 3D printed case for the stopwatch and accompanying components was made. It is expected to make more stopwatches for a drone race with the NewBeeDrones. One issue to solve with these gates is to edit the code or build for the ultrasonic sensors to be more sensitive to data and have more accurate time recordings

Environmental fatigue of an Al-Li-Cu alloy. Part 3: Modeling of crack tip hydrogen damage

Environmental fatigue crack propagation rates and microscopic damage modes in Al-Li-Cu alloy 2090 (Parts 1 and 2) are described by a crack tip process zone model based on hydrogen embrittlement. Da/dN sub ENV equates to discontinuous crack advance over a distance, delta a, determined by dislocation transport of dissolved hydrogen at plastic strains above a critical value; and to the number of load cycles, delta N, required to hydrogenate process zone trap sites that fracture according to a local hydrogen concentration-tensile stress criterion. Transgranular (100) cracking occurs for process zones smaller than the subgrain size, and due to lattice decohesion or hydride formation. Intersubgranular cracking dominates when the process zone encompasses one or more subgrains so that dislocation transport provides hydrogen to strong boundary trapping sites. Multi-sloped log da/dN-log delta K behavior is produced by process zone plastic strain-hydrogen-microstructure interactions, and is determined by the DK dependent rates and proportions of each parallel cracking mode. Absolute values of the exponents and the preexponential coefficients are not predictable; however, fractographic measurements theta sub i coupled with fatigue crack propagation data for alloy 2090 established that the process zone model correctly describes fatigue crack propagation kinetics. Crack surface films hinder hydrogen uptake and reduce da/dN and alter the proportions of each fatigue crack propagation mode

Natural History of the red-spotted newt, Notophthalmus viridescens viridescens (Rafinesque), in West Virginia

Many studies have been conducted on Notophthalmus viridescens viridescens but none have occurred in West Virginia. There are variations in the life history of newts depending on location. In this study, I studied a population of newts in Wayne County, West Virginia from February 1996 to June 1997. I examined population structure, seasonal activity, and reproductive biology. The population structure can be divided into four classes: egg, larvae, eft, and adult. Eggs at Shoals were deposited in mid-May and larvae were present from mid-June to early September. Larvae began to transform at an approximate total length of 32.8 mm. Red efts were not studied at Shoals but their sizes ranged from a total length of 28.3 mm to a minimum of 78.3 mm. Adult snout-vent length ranged from 41.7-64.0 mm and averaged 49.3 mm. The sex ratio of adults varied weekly. I captured up to 27 males for every female (27:1) in funnel traps in February and March. In summer, however, females outnumbered males up to 2.5 times The overall sex ratio in funnel traps was 5.1:1. While dipnetting, however, the weekly sex ratios were much closer to even. Overall, from December to June, the sex ratio was 1:1.4. According to current literature, this is the first population of newts studied where females outnumber males. Seasonal activity patterns of male and female adult newts differ. Sex ratios in funnel traps reflect activity ratios since the traps capture moving animals. Males are much more active than females in the late fall and early spring. While dipnetting, females were captured more often from vegetation. There are also more females in the water in the summer. Most of the newts at Shoals emigrate from the ponds to terrestrial hibernacula in late April. This migration correlates with the increase in water temperature. Over the summer, newts were found under cover objects and debris. Their skin texture and color and tail height is more suitable for terrestrial living. Newts return to the aquatic environment in mid-November, when ponds refill and water temperature begins to drop in mid-November. Reproductive biology is divided into the breeding migration, breeding season, and oviposition. There are two breeding migrations at Shoals, one in November and one in February/ and March. In other studies, the smallest adults, metamorphing efts, migrate to ponds in the fall. At Shoals, the smallest adults migrated in the spring. Also, it appears that females do not reproduce their first year. Current literature describes only a spring breeding season and occasionally a false fall breeding season9. At Shoals, breeding actually occurs at both seasons. This is determined by looking at sperm waves in males, which showed sperm throughout the entire reproductive tract from November to May, and by witnessing males drop spermataphores in December. Oviposition was determined visually and by monitoring female egg volume throughout the year. Both of these methods coincided and showed that eggs are deposited in May and June

Letter from Sophia K. Piascik to Rev. Robert L. Pelkington, O.P.

Providence College Department of Theatre, Dance & Film Letter from Sophia K. Piascik (Alumni Office at P.C.) to Rev. Robert L. Pelkington, O.P. regarding the production of Man of La Mancha March 16, 1973https://digitalcommons.providence.edu/lamancha_commentary/1000/thumbnail.jp

The Growth of Small Corrosion Fatigue Cracks in Alloy 7075

The corrosion fatigue crack growth characteristics of small (greater than 35 micrometers) surface and corner cracks in aluminum alloy 7075 is established. The early stage of crack growth is studied by performing in situ long focal length microscope (500) crack length measurements in laboratory air and 1% sodium chloride (NaCl) environments. To quantify the "small crack effect" in the corrosive environment, the corrosion fatigue crack propagation behavior of small cracks is compared to long through-the-thickness cracks grown under identical experimental conditions. In salt water, long crack constant K(sub max) growth rates are similar to small crack da/dN