Materials Engineering

The Mitigation of Eutrophication Using Microporous Polymer Membranes to Control Algae Growth

Christopher R. Riley — Mon, 17 Jun 2013 13:01:39 PDT

A system was designed to mitigate the accelerated process of anthropogenic eutrophication. This system aimed to contain Chlorella Vulgaris microalgae cells within an enclosed polymer membrane pouch while allowing for water and nutrients to diffuse through the pouch. As a test model, a 10 gallon aquarium was partitioned into three sections using polycarbonate membranes with 1 micron pore diameters. Each section was then gradually filled with a deionized water and Bristol solution recommended for microalgae growth. Phosphate and nitrate were added to Section A of the aquarium and allowed to diffuse throughout the tank. A water pump was used to agitate the solution and increase the diffusion rates of the nutrients. Samples were drawn periodically from section A and section C. A spectrophotometer was then used to analyze the phosphate and nitrate concentration of the samples. The resulting diffusion rates were graphed for trials with and without Chlorella Vulgaris cells present in section B of the tank to quantify the rate and overall amount of nutrient absorption by this microalgae.

The membrane was shown to successfully contain the microalgae cells within section B, so long as it was properly adhered to the aquarium. Both nitrate and phosphate were readily able to permeate the polycarbonate membrane and diffuse throughout the tank. Quantitative analysis of chlorella cell population failed to yield representative data. However, qualitative observations found that microalgae growth had occurred within Section B. Nutrient diffusion trends were highly linear. With the exception of two data sets that had substantially lower values, all data sets demonstrated R² values of at least 0.9059 and 0.985 at the highest. This behavior was contrary to that predicted prior to conducting the experiment.

As anticipated, rates of nutrient concentration change into Section C were lower when chlorella was present in Section B than when it was not added to the system. For phosphate, the rate at which this concentration increased in Section C was 1.4 µg/L/min lower when chlorella was added to Section B. For nitrate, the rate of concentration increase in Section C was 11 µg/L/min lower when chlorella was added to Section B. These results suggest that microalgae within the tank was successful in absorbing both nitrate and phosphate as they diffused throughout the tank.

Overall, results suggest that the proposed system would be able to absorb excess nutrients present within a eutrophic water system, thereby mitigating the ill effects of this biological state. However, collected results were based on a limited number of trials and thus were not robust. Further investigation should be undertaken to confirm the quantitative results obtained in this project.

Al₂O₃ Oxide Morphology for Two Fe-Cr-Al Stainless Steel Foils Used in Gasoline Engine Catalytic Converters

Jennifer Suiter — Mon, 17 Dec 2012 12:32:22 PST

Corrugated 0.05 in thick strips of Fe-Cr-Al ferritic stainless steel samples with 4% and 6% aluminum were heat treated, and the resulting Al₂O₃ oxide was analyzed using SEM imaging. Three heat treatment cycles were carried out for each sample. The heat treatments were based on future metal-substrate catalytic converter processing prior to applying the washcoat Each heat treatment started with a 90 minute ramp from room temperature to 538°C and a 32.5 minute ramp from 538°C to 899°C. The three different dwell periods at 899°C were 4 hours, 6 hours, and taking a sample out every hour for 4 hours and letting it air cool. The full 4 and 6 hour cycles were finished with an in-furnace cool recorded by an external thermocouple and datalogger. Additional samples were included in the 6 hour cycle that were flattened by pressing a metal cylinder across the top of the corrugated sheet. All samples were sputtered with a 300-Å-thick layer of gold to improve resolution in the SEM. Cold rolling to form the 0.05 in sheet and possibly the corrugation deformed the microstructure and altered the surface, which produced different oxide structures during heat treatment in linear patterns. Also, the different regions of the corrugation (ridge, valley and slope) produced different oxide formations. The ridges showed a flatter oxide, the valleys showed a linear pattern with alternating needle-like and rough granular oxides, and the slopes showed needle-like oxide with patches of smooth rounded oxide. The desired oxide is a needle-like structure which provides a large surface area for the catalyst layer (washcoat) during the production of catalytic converters.

Analyzing the Corrosion Resistance of Ni-Shield 200 Coatings at Different Temperatures When Exposed to Sulphuric Acid

Alex Hussinger — Mon, 17 Dec 2012 12:32:19 PST

Six steel samples each were twin wire arc sprayed with Hastelloy C-276 or Nickel-Shield 200 coatings approximately 0.020″ thick. These samples were then cut into 3″ by 3″ squares. A 2″ diamond grit hole saw was used to abrade and polish to a smooth surface a ring in the middle in order to get an O-ring mechanical seal. The samples were then weighed and loaded into a jig that started from the bottom up with a stainless steel plate, then the sample, then a Viton O-ring, a ¾″ thick glass plate with a 1 3/4″ hole cut in it, another O-ring, and then another stainless steel plate. The plates were bolted together tightly in the corners. This setup was designed to expose only the top surface of the coated sample to sulphuric acid, which is an accurate representation of an application of the coating. The samples were tested with 98% concentrated sulphuric acid at room temperature, 100⁰F, and 200⁰F over a period of 2 weeks. The corrosion rates could not be calculated accurately due to leakage of the sulphuric acid onto the sample. However, there were macroscopic signs of corrosion product on the Ni-Shield 200 samples that were not present on the Hastelloy C-276 samples. The microstructures of both samples also showed signs of surface attack. While a precise corrosion mechanism could not be identified, the Ni-Shield 200 sample did react with the sulphuric acid enough to warrant further study into its mechanisms and methods.

Discontinuous Grain Boundaries of Forged René 41

Steven Crump — Thu, 13 Sep 2012 11:32:49 PDT

Forged components must pass a grain size specification (grain size, distribution) for acceptance in an application. The varying amounts of plastic deformation during forging can lead to abnormally large recrystallized grain sizes in certain regions of the part, which will not pass specification. The question exists whether these abnormally coarse grains are truly comprised of poly crystalline fine grains with grain boundaries resistant to etching techniques. To investigate this abnormal grain size effect, a cross section of a forged René 41 nickel-based superalloy aircraft engine ring was cut and sectioned into six segments. Those segments were then prepared for microstructural analysis using a 95% HCl and 5% H₂O₂ etch typical of metallographic testing companies. The results indicated an apparent segregation of the grains with multiple regions showing a few abnormally large grains surrounded by much smaller ones. A fine grain size dominated some samples (ASTM grain size 5 to 7), these would pass specification. Other regions showed intermittent large grains (ASTM grain size 1 to 2). The presence of annealing twins within the large grains proved that these larger grains were single grains, but their true size is masked by discontinuous boundaries throughout. The abnormally large grains followed some flow pattern suggesting their manifestation may be a function of how much strain was applied to that section of the alloy during forging. Scanning electron microscopy (SEM) in conjunction with electron backscatter diffraction (EBSD), determined the orientation and size of each grain on a map and identified grains independently of etching grain boundaries. As a result, the discontinuous grain boundaries in question were determined to be low angle grain boundaries that were resistant to chemical attack by the etchant.

Morphology and Roughness of Al2O3 on Ferritic Stainless Steel Foil for Diesel Catalytic Converter Applications

Megan Butala — Thu, 13 Sep 2012 11:32:44 PDT

The improved thermal properties of metal-substrate catalytic converters enable effective catalysis sooner after ignition than traditional ceramic monoliths, resulting in less harmful emissions. ACAT Global, a manufacturer of stainless steel catalytic converters, uses ferritic stainless steel substrates for low temperature catalytic converters for diesel automobiles. Production begins with an oxidizing heat treatment to increase surface roughness. The success of the second production step, the application of catalyst-containing ceramic slurry (washcoat), depends on the surface roughness that results from oxidation. Formation of the primary oxide of interest, alumina (Al₂O₃), is controlled by the stainless steel foil composition, oxidation temperature, and oxidation time. ACAT intends to use a specific foil, so composition will be constant. Temperature will also be constant; 900°C is most likely to result in growth of rough alumina since diffusion of aluminum to the surface is faster than the diffusion of oxygen into the material at that temperature. This project focuses on the effect of the last parameter, treatment time, on oxide morphology and roughness. Samples were removed at hour intervals of a six hour 900°C hold. Qualitative assessment of surface morphology was performed using SEM, revealing that “rough” oxide resulted from treatment times exceeding three hours at temperature. Additionally, SEM images revealed an increase in the frequency and magnitude of surface features with increasing treatment time and a decrease in the frequency and size of dark regions of smooth oxide. Profilometry was used to collect R_a roughness values of the rough oxide samples. Average profile roughness increased from 217 nm for the untreated foil to a maximum value of 564 nm for the five hour sample. The decrease in R_a from five to six hour samples was unexpected and could be a consequence of limited vertical resolution of the profilometer settings. Oxidation times of four, five, and six hours appear to have the rough morphology preferred for washcoat adhesion. Specific interactions of the washcoat with features of various heights and lateral spacings should be assessed to determine ideal oxidation time.

EFFECT OF HEATING TEMPERATURE, HEATING TIME AND INITIAL MICROSTRUCTURE ON RECRYSTALLIZATION OF WASPALOY DURING HEATING FOR FORGING

Marissa Hill — Thu, 13 Sep 2012 11:32:40 PDT

A fine, uniform grain size is required for creep limited Waspaloy in aircraft engine applications. Upon heating, Waspaloy does not always recrystallize in a uniform manner resulting in occasional large grains with a majority of the grains meeting the grain size requirements. Waspaloy’s microstructure was analyzed with different heat treatments and in the as-forged condition. The strengthening mechanism is the gamma prime phase. The gamma prime solvus temperature is 1908°F so the different heat treatments were determined around that temperature, as well as the forging temperature range of 1800-2150°F. At the 1850°F heat treatment, the microstructure recrystallized with small grains, slightly larger than the as-forged samples. The samples heat treated at 1900°F had microstructures showing the sample recrystallized with larger grains surrounding the smaller grains with an ASTM grain size 5. The samples heat treated at 1925°F appeared similar to the samples that were heat treated at 1900°F, but had an ASTM grain size number slightly larger with an ASTM grain size number of 4.76. The samples heat treated at 1950°F showed larger grains than the previous heat treatments with an ASTM grain size 3.92. The samples heat treated at 2000°F showed much larger grains than the other heat treatments. The average grain size for the samples at 2000°F were about 2.4. The samples fell into the ASTM grain size number requirement for Schlosser at an ASTM grain size of 3 or finer, except for the heat treatments at 2000°F. The as-forged sample was approximately ASTM grain size 6. The recommended heat treatment temperature is 1925°F because it has the gamma prime strengthening mechanism and complies with Schlosser’s ASTM grain size number specification requirements.

BIAXIAL & TWIST TESTING OF COMPOSITE CARBON-FIBER SANDWICH PANELS FOR AUTOMOTIVE RACING VEHICLES

Erik Eckberg — Thu, 13 Sep 2012 11:32:35 PDT

Composite sandwich panels were constructed with 4-ply plain weave carbon-fiber/epoxy face sheets in the 0^o/45^o/0^o/45^o orientation and 1/8^th inch Nomex honeycomb core. The panels were cut into 5-inch square test plates for mechanical testing. All testing was done on a fixture designed and fabricated by Pratt & Miller Engineering and installed on an Instron testing system at Cal Poly. The twist test was performed by supporting diagonal corners of the plate while simultaneously loading the opposite two corners at a crosshead rate of .06 in/min (ASTM 3044-94R11). Out of 10 panels tested, six were tested longitudinally, with the L direction of the honeycomb parallel to the front of the test plate, and four were tested in the transverse orientation, with the L direction of the honeycomb perpendicular to the front of the plate. The average compliance for the longitudinal loading was 1.303 mil/lb, and the transverse loading was 1.394 mil/lb. The panels failed with a combination core shear failure and face-to-core debonding. The anisotropic nature of the honeycomb core supports the difference in the compliance of the panels; however the complex loading of the twist test results the difference being not statistically significant. The biaxial bending tests involved supporting the composite plate on each corner and loading it in the center. In 5 tested plates, the measured average compliance was .4363 mil/lb with face-to-core debonding being the primary failure mode. The results of these tests will be used to improve existing FEA models for the performance of racing vehicle composite panels.

Analysis of Failed Forging Saddling Mandrels and Process Improvements for Increased Mandrel Lifespan

Brock Costalupes — Thu, 13 Sep 2012 11:32:32 PDT

This project seeks to increase the lifespan of steel mandrels used by Schlosser Forge in the saddling process, which is part of the production of forged rings for the aerospace and power generation industries. All saddle mandrel samples were taken from used 4340 steel mandrels. Hardness profiles were measured across rectangular bars cut from the transverse direction of a completely fractured piece of a 7″ diameter mandrel. The hardness near one outer surface of the tested bar was 36 HRC and gradually decreased to 30.5 HRC at the opposite surface. Macroscopic examination of the primary fracture surface along with light microscope imaging of fracture surface feature details suggests that the failure mechanism is likely related to reversed bending fatigue rather than deterioration of the mechanical properties of the steel due to microstructural changes from in-process overtempering during saddling. Cyclic softening of the quenched and tempered steel caused by the saddling process adversely affects the ability of the steel to withstand fatigue. Different heat treatments were conducted to compare the resulting toughness, measured by Charpy impact test, to that of the current process of quenching and tempering the mandrel to a hardness of 38 – 42 HRC. Each heat treatment involved austenitizing at 1500°F for one hour. By varying the tempering temperature, with a constant two hour tempering time, samples were obtained at 28.5 HRC, 39.8 HRC, and 42.5 HRC. Charpy impact energy decreased significantly as hardness increased. An additional heat treatment was conducted where a 4340 steel sample was austenitized, quenched in a 660°F NaNO₃-based molten salt bath and held for two hours. The result of this heat treatment is a bainitic structure, which may show improved toughness.

Characterization of Positive Macrosegregation at the Subsurface of Direct-Chill Cast 7050 Aluminum Forging Billets

Aaron Youril — Thu, 13 Sep 2012 11:32:26 PDT

Segregation of alloying elements during casting of forging billets may persist to the final forged component leading to unacceptable surface appearance. Determination of the elements or compounds that segregate is the essential first step to solving this problem. Differential Scanning Calorimetry (DSC) was used to determine a composition profile of the macrosegregation occurring at the subsurface of an as-cast 7050 aluminum alloy billet. Data collection was carried out by separating 10 to 20 mg samples from the outer centimeter along the radius of the billet, as well as samples from the bulk interior of the billet for comparison with the nominal alloy composition. DSC analysis was performed using platinum capsules on the Exstar DSC6000, from 20°C to 600°C at a rate of 5°C/min over the temperature range of interest. DSC scans showed heat flow peaks for incipient melting and crystallization transformations for Al₂CuMg (S-phase). Size comparison of DSC peaks provided data about the relative masses at each distance from the surface. The partial heat of fusion of samples of several depth profiles was used to determine relative mass fractions as compared to a bulk sample. A sharp increase in S-phase concentration was observed near the surface and a drastic decrease at approximately 3 mm from the surface, followed by a return to bulk alloy values after 5 mm due to shrinkage-induced flow in the casting process.

THE EFFECT OF FORGING TEMPERATURE ON CARBIDE PRECIPITATION AND DUCTILITY OF HAYNES 230 NICKEL-BASED SUPERALLOY

Thomas Chludzinski — Thu, 13 Sep 2012 11:32:22 PDT

Samples of Haynes 230 nickel-based superalloy were taken from forgings at Carlton Forge Works. These samples represented components that passed and failed ductility specification. Metallographic measurements of particle size and intergranular particle count were taken from 25 locations across the sample. Carbide particles at the grain boundaries were equal size, averaging 13.0 μm in diameter. The low ductility samples contained an average of twelve particles per 250 μm of grain boundary, high ductility samples contained an average of only four particles along the same grain boundary length. To determine the effects of forging temperature on carbide distribution in the microstructure, three 4-in-diameter, 4-in-height Haynes 230 billets were upset forged to 7-in-diameter, 1-in-height at 2050°F, 2150°F, and 2250°F. For each forging, samples were removed and solutionized at 2150°F, 2200°F, and 2250°F for 45 minutes. Each combination of forging temperature and solutionizing temperature was tensile tested to determine yield strength and ductility. Results showed the alloy increased ductility with forging temperature, which corresponded to decreased particle count. Mechanical properties were altered less prominently with solutionizing temperature, but a small increase in tensile strength and decrease in ductility was associated with higher temperature solutionizing, accompanied by a decreased particle size. Particle count and distribution were found to the key factor in determining ductility of the material. Forging at low temperatures causes plastic deformation at the grain boundaries, providing a low energy nucleation site for migrating carbon in solution, thereby increasing the number of particles in the forged pieces. The optimal combination of ductility and yield strength occurred at 2150°F forging temperature and 2200°F solutionizing temperature.

Effects of Beta Stabilizers on Quench Delay Susceptibility of Ti-6Al-4V

Kyle Logan — Thu, 13 Sep 2012 11:32:15 PDT

Tensile samples of Titanium 6Al-4V (Ti-6Al-4V) were machined from forgings containing rich and poor amounts of beta stabilizers in their compositions. The tensile samples were each heat treated two times. In the first round of heat treatments, the samples were either beta solution treated (BST), or solution treated (ST). Each sample was water quenched with varying quench delays of 10, 20, and 30 seconds. BST treated specimens were then overaged at 1350°F for 2 hours and air cooled (BSTOA); while the ST treated samples were aged at 990°F for 6 hours and air cooled (STA). Following heat treating, the tensile samples were chemically milled to remove the alpha case layer from the surface, and then tensile tested using an Instron Tensile Testing System. Beta stabilizer rich bars that were BSTOA treated with a quench delay of 10 seconds resulted in an average ultimate tensile strength (UTS) of 154 ksi, and average yield strength (YS) of 144 ksi. Beta stabilizer poor, BSTOA treated bars with the same quench delay of 10 seconds, resulted in similar average UTS and YS values of 155 and 145, respectively. Increasing quench delays of BSTOA treated bars to 30 seconds did not alter the resulting average mechanical properties. The beta stabilizer rich bars that were STA treated with a 10 second quench delay resulted in average UTS of 167 ksi and average YS of 154 ksi. Mechanical properties were slightly lowered for beta stabilizer poor, STA treated bars with 10 second quench delays; resulting in average UTS of 166 ksi and YS of 152 ksi. Average properties of both beta rich and beta poor samples that underwent STA heat treatments dropped when the quench delays were 30 seconds.

Effects of Annealing/Solution Treating and Aging on Longitudinal and Transverse Properties of Ti-6Al-4V Forgings

Blake Reller — Thu, 13 Sep 2012 11:32:12 PDT

Forty-eight subsize round-bar tensile samples (ASTM E8) were machined from 3-in-thick forgings of Ti-6Al-4V. Half of these samples were cut so the axis aligned with the longitudinal (LG) direction of the forging, the other half were cut to align with the transverse (LT) direction. Four samples from each direction were subjected to one of six heat treatments so that a total of eight samples received each treatment. Annealed samples were held at 1350°F for two hours, then air cooled. Solution treated and aged (STA) samples were solution treated at one of five temperatures between 1785°F and 1435°F for one hour and then water quenched after a 25 second quench delay in air. Following quenching, all STA samples were aged for 6 hours at 990°F, then air cooled. Prior to tensile testing, the samples were sent back to Weber Metals for chemical milling to remove the brittle alpha-case surface layer formed during heat treatment. A polymer coating was applied to the samples’ threaded ends so only the gage length would be milled, and any oxide present was sanded off to avoid preferential etching. Tensile tests showed anisotropy primarily in Tensile strength with the LT direction testing 3-7 ksi higher than the LG direction. A general linear model found a significant difference of Tensile strengths between directions in all heat treatments except for STA 1, which had the highest solution treating temperature. A difference of about 7 ksi was also found between STA 5 samples in Yield strength. No anisotropy was observed in Elongation. It was concluded that higher solution-treating temperatures decreased anisotropy by transforming the textured alpha into beta, effectively erasing any alignment. It was also concluded that the LT direction is stronger than the LG due to non-preferred slip systems being the primary mechanism of deformation.

Correlation Between 90o Tensile and 90o Flexural Properties for Thermoplastic Based Carbon-Fiber Composites

Amy Lautenbach — Thu, 13 Sep 2012 11:32:02 PDT

Thermoplastic matrix composites containing carbon fibers and 4 different resins (TP 1-TP 4) were tested in tension with the fibers at 90 degree to the longitudinal axis following ASTM D 3039-00. The tensile strengths varied from 5.07-13.87 ksi with TP 1 as the strongest, and TP 4 as the weakest. SEM images were taken of the fracture surface of the samples to explore the fiber-matrix interaction. The SEM images showed significantly more wetting of the fibers in the higher strength materials. The SEM images of the two stronger materials showed resin coating the fibers even after fracture while the two weaker materials showed a clean interface between the fibers and resin. As the second portion of the project, 3 and 4 point bend tests were conducted on the same 4 composite materials with a support span width of 1.4 inches according to ASTM D 790-03 and ASTM D 6272-02. The fibers were oriented 90 degrees to the long axis of the samples. The 3 point bend test flexural strength values ranged from 8.30-21.73 ksi and the 4 point values ranged from 6.26-19.25 ksi. The only discrepancy with the data points was TP 1 was not consistently stronger than TP 2. Data analysis was run using the STAT17 program to confirm that the TP 1 and TP 2 strength values were comparable and thus the inconsistency was not relevant. The flexural strength values were graphed versus the tensile strength values and showed a strong correlation. The 3 point binding strength versus tensile strength graph had an R² value of 0.9894 and the corresponding 4 point binding versus tensile graph had an R² value of 0.9979.

Characterization and Analysis of Low Room Temperature Ductility Nickel-Based Superalloy 718 Plus for Aircraft Engine Forgings

Jonathon Bracci — Thu, 13 Sep 2012 11:31:57 PDT

Schlosser Forge Co. forges low pressure turbine (LPT) cases from the nickel based superalloy 718 Plus using the ring rolling forging process. Schlosser has been experiencing low room temperature ductility problems in a number of their 718 Plus LPT cases. LPT cases are required to pass a 4D tensile test at room temperature with a minimum of 15 percent elongation. The ductility problem was reduced by increasing the forging temperature from 1825˚F to 1850˚F. Analysis was performed on 718 Plus samples taken from forged LPT cases that failed the room temperature ductility requirement and ones that passed the requirement. The analysis required conducting grain size measurements and delta phase volume fraction measurements to relate these microstructural characteristics to low room temperature ductility. Samples of 718 Plus were mounted and polished for metallography in accordance with ASTM E3-11. Samples were etched with modified Kalling’s reagent for 3 minutes and grain size measurements were taken per ASTM E112-10. Grain sizes varied only slightly between the low and acceptable ductility samples, with an average grain diameter of 44.9 μm. Grain size variation was not contributing to the low room temperature ductility problem. The samples were then re-polished to remove the previous etch and re-etched with modified Kalling’s for 30 seconds. The 30 second etch allowed the delta phase precipitates to be revealed while leaving the grain boundaries un-etched. Volume fraction measurements of the delta phase precipitates were taken per ASTM E562-11. Results showed the low ductility sample contained the highest amount of delta, about 7.5 percent by volume. The amount of delta was found to be inversely proportional to ductility as well as forging temperature.

Synthesis of White Cadmium-Selenium Quantum Dots

Kyle Reilly — Wed, 15 Aug 2012 15:11:39 PDT

A process was developed for the synthesis of cadmium-selenium quantum dots that fluoresce at multiple wavelengths, giving a white color to the solution. The process involved making a selenium pre-cursor, then a cadmium precursor, then injecting the selenium precursor into the cadmium precursor and extracting a sample. Once the a repeatable process for synthesizing white quantum dots was developed, the absorption and fluorescence was measured and recorded over a period of two weeks. In the development of the process, the key variables were the temperature of the cadmium precursor and the time between injecting the selenium precursor and extracting the sample. Extracting the quantum dots within the first second of injection and using a temperature of 220 ±6 °C repeatedly yielded the desired white quantum dots. The white dots exhibited three main fluorescence peaks: at 430-450 nm, 560-580 nm and 610-620 nm. The sample dots showed absorbance from 250 nm to 310 nm. Over time as the quantum dots remained in solution, the peaks shifted to higher wavelengths by 18.5 nm over two weeks, and the intensity decreased by 46%. The shift was caused by growth of the quantum dots over time, but did not significantly affect the visible white color of the dots. The testing showed white quantum dots could be made using a repeatable process with potential applications in white light LED technology.

Improving Solar Cell Performance Using CdSe/ZnS Core/Shell Quantum Dots in a Spectral Conversion System

Buddy Bump — Wed, 08 Aug 2012 08:35:35 PDT

Solar cells have been found to absorb light more efficiently and effectively when the energy of incoming photons matches the electronic band gap of the solar cell. Spectral conversion of light from UV to lower energy wavelengths can improve solar cell efficiency an estimated 14.5%. Cadmium Selenium/Zinc Sulfide Core/Shell quantum dots have been successfully embedded in PDMS silicone elastomer. Using a Keithley 2400 Electrometer with Labview software, voltage and current characteristics have been recorded in steps of 10 mV with a wait time of 250 ms on a commercially available solar cell using an artificial solar spectrum created by a Tungsten Halogen lamp. The commercially available solar cell was found to have a maximum power output of 250 mW and a fill factor of 71.025%. Short term repeatability testing and long term reproducibility testing was conducted using a sample size of ten and a wait time of 1 hour and 1 day respectively, repeated five times. The system was found to have a long term reproducibility of 0.010% and a short term repeatability of 0.004% after a one hour warm-up period to reach a thermal equilibrium. Three mechanisms of light attenuation have been observed due to PDMS: the addition of interfaces, surface adhesion, and thickness. The most substantial loss was created by the addition of interfaces which decreased the fill factor of the solar cell by 0.00839 or 1.18%. Losses from surface adhesion and losses due to increasing thickness were minimal. The CdSe/ZnS core/shell quantum dots used fluoresced at a wavelength of 570 nm. These quantum dots were dried from octadecane and then suspended in toluene before being mixed with bulk PDMS to create the spectral converter. The spectral converter increased short circuit current by 1% and did not change open circuit voltage or fill factor. The maximum power was increased to be equal to that of the bare solar cell.

Effects of Abrasive Particles on the Projected Fatigue Life of Nylon Climbing Rope

Casey Johnson et al. — Mon, 30 Jul 2012 12:19:09 PDT

When climbing rope is used outdoors, it is exposed to foreign particles such as sand and silt. These particles can potentially work their way through a rope’s sheath and damage the load bearing core decreasing the rope’s strength without exhibiting obvious wear. This project quantified the effect of abrasive particles on the fatigue life of nylon climbing rope. The experimental design involved 18 pieces of static nylon rope of kernmantle construction. 9 of these samples were heavy agitated in a slurry of water, silt, sand and soil, and left to sit for 24 hours. The remaining 9 samples were submerged in clean water for the same period. Two sections of rope from each the dirty and clean groups were fatigued at 100, 200, 300, 400 cycles and one section each at 500 cycles. After fatigue treatment, the rope was tensile tested. Comparisons were made between the strengths of the dirty rope samples and the clean rope samples. It was found that exposure to abrasive particles decreases the fatigue life of the rope. It should be noted that the clean and dirty rope segments had identical strengths before fatigue treatment (5500lb break strength), the same as that of new rope (100% overall strength). Once exposed to fatigue treatment, the dirty ropes’ overall strength dropped linearly with greater fatigue. There was a maximum drop in strength of 63% and a minimum drop in strength of 22% in the dirty rope group. The maximum decrease in strength of the clean rope was 25% with a minimum of 2%. It can be concluded that proper cleaning and care is essential to maintaining strong, safe ropes.

Residential Water System Circuit Breaker for Monitoring of Abnormal Use

Griffin Beemiller — Thu, 26 Jul 2012 15:25:01 PDT

Wireless Temperature Monitoring System for the Cal Poly Pilot Winery

Caitlin Devaney — Mon, 09 Jul 2012 10:09:32 PDT

This project, with an interdisciplinary group of two computer engineers and one materials engineer, was seeking to implement an automated temperature monitoring system which is affordable and easy to use, as well as adaptable to any arrangement and scale of a winemaker’s fermentation setup. My goal, as the materials engineer, was to design, fabricate, and test the enclosure, for the wireless nodes that are placed in the wine fermentation tanks, and the materials used for the node enclosure. For the enclosure of the system, materials selection was completed using CES software using limitations of only polymer materials which absorb less than 0.01% of water in a 24 hour period, are resistant to weak acids, cost-effective, and have a high stiffness. The material which passed all of the stages and was chosen for the design of the node enclosure was high density polyethylene (HDPE). However, to make sure that HDPE and the adhesive used to connect to individual HDPE components (PDMS) can withstand the fermenting wine environment, a two-week long preliminary test was completed. It was found that PDMS had the greatest difference in water adsorption between day 0 to day 1 and 20. HDPE had the greatest difference in water adsorption between day 20 to day 0 and 1. PS did not change. All of these changes in water adsorption were around the required limit set in the materials selection process of 0.01%. Then to make sure the PDMS adhesive could withstand the cleaning chemicals (sodium hydroxide, NaOH, and citric acid) used at the winery, a week-long degradation test was completed and found the PDMS sample’s surface changed when exposed to a sodium hydroxide solution. The PDMS samples which were exposed to the diluted citric acid solution, around 3%, had the greatest strength, average of 2.73 MPa compared to the control average of 1.2 MPa due to stress relaxation by the formation of silanols, but could also be due to the run order and human error. However, all of these changes are minor enough to where it would not affect the reliability of the node enclosure. The design was then made and a cost analysis and life cycle analysis was completed.

Design and Development of an Interactive Materials-Based Learning Kit for K-4 Grade Levels

Thomas Agasid et al. — Tue, 19 Jun 2012 16:26:48 PDT

The Materials Safari Adventure kit was designed to help introduce basic materials concepts to young audiences in kindergarten through fourth grade levels. The primary goal of this project was to design a tool to spark an interest in materials science for young children, while revealing the field of materials science to parents and educators. The final kit design incorporates a safari theme to encourage imagination and promote self-directed learning through the interaction with materials. Materials were selected to showcase a range of properties within three materials classes: metals, polymers, and natural woods. A total of 9 materials were chosen for the kit, including: a-36 mild steel, 6061 T6 aluminum, 360 alloy brass, clear cast acrylic, ABS plastic, rosewood, oak, and balsa wood. The metal materials were water jet cut followed by hand filing and sanding, the woods and acrylic were laser cut, and the ABS was rapid prototyped using a 3-D printer into the profile shapes of various safari animals. The kit consists of three testing stations designed to examine weight, density, and magnetism. Prototype testing was conducted at the Cal Poly child development lab and the San Luis Obispo Children’s Museum. Through prototype testing, we gained a greater understanding of our user and tailored the kit to better suit their learning needs. Additionally, testing verified the sizes of the animal pieces, ⅜” thick, between 1 to 2.25” in width, and 1.2” to 2.25” in height to be appropriate even for our youngest users. The safari theme was able to cultivate interest and motivation in users. The Materials Safari Adventure was able to successfully demonstrate and portray educational concepts presented at the testing stations, verified by the user’s ability to correctly answer application driven questions.