Oscar Suarez | University of Puerto Rico Mayaguez (original) (raw)

Papers by Oscar Suarez

Revista De Metalurgia, Jun 30, 2004

International Journal of Cast Metals Research, Nov 1, 2000

Late sulphur additions to post-inoculated high silicon ductile irons were studied by means of mic... more Late sulphur additions to post-inoculated high silicon ductile irons were studied by means of microstructural characterisation and thermal analysis, complemented with statistical tools, image analysis and thermodynamic modeling. Using a 4.31 % carbon equivalent iron melt, two low sulphur levels were investigated in an equivalent post-inoculated iron: 0.005 wt.% and 0.012 wt.% S, where the higher sulphur level was produced by the addition of iron sulfide after treatment and inoculation. A thorough image analysis was used for graphite particle characterisation and fraction ferrite, revealing that, under these experimental conditions, sulphur does not significantly affect the iron nodularity at the investigated levels. Two Weibull distributions fitted to the frequency distributions of the graphite shape factor in both iron sample sets indicated that there were no significant differences between shape factor populations. In addition, nodule counts increased with addition of sulphur to the post-inoculated iron. A larger amount of ferrite was detected in the higher sulphur ductile iron, and was attributed to the higher nodule count. The use of the inverse cooling rate method made it possible to verify this correlation by inspecting thermal events in the eutectoid range. A more energetic reaction in the higher sulphur iron upon cooling was attributed to the formation of more ferrite. Differential thermal analysis was used to evaluate those results and thermodynamic modeling of phase formation in an equivalent Fe-C-Si was used to validate the overall findings. Finally, the inverse cooling rate method was demonstrated to be a reliable and robust tool when minor differences in solid state transformations are investigated.

The AA5182 Al-Mg alloy is used in applications where high formability and strength are required l... more The AA5182 Al-Mg alloy is used in applications where high formability and strength are required like container ends, can stocks, reinforcement members and automotive parts. With convenient heat treatments the alloy strength increases and it can be used in aerospace applications. In the present research Al-Mg aluminum beverage can tabs were heat treated within a temperature range between 170ºC and 450ºC beginning with solubility and then aging treatment. The tabs were tested under low-cycle fatigue conditions. The fatigue strength measured by the number of loading cycles increased in the first two hours of exposure to the aging treatment at any temperature. The maximum resistance was reached at 2.5 hours. After this time it dropped in all treatments except for the 270ºC treatment, where it decreased gradually. The fatigue strength increment could not be defined since the geometry of the tab affected the type of fracture and the number well of cycles. In the microstructure, the formation of precipitates at low temperature (aging 170 ºC and 270 ºC) caused a low fatigue resistance in the material. However at high temperatures (370ºC) the treatment facilitated precipitates dissolution reinforcing the aluminum matrix and making it more resistant.

Construction and Building Materials, Apr 1, 2013

h i g h l i g h t s " We study the rheological and hardened properties of micro and nano-SiO 2 in... more h i g h l i g h t s " We study the rheological and hardened properties of micro and nano-SiO 2 in superplasticized cementitious mixes. " Mineral admixtures decrease the flow times and saturation dosages compared to superplasticized-control samples. " Under superplasticized conditions nS-grouts improved its rheological behavior at low w/b ratios and replacements levels. " Flow area, fresh density and air content exhibit a nonlinear dependence with mineral and chemical admixtures. " Improvements in compressive strength in nS-systems are due to both densification and filler effect of the ITZ.

Crystals, Apr 28, 2021

This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY

Proceedings of the 20th LACCEI International Multi-Conference for Engineering, Education and Technology: “Education, Research and Leadership in Post-pandemic Engineering: Resilient, Inclusive and Sustainable Actions”

This work analyzes fatigue resistance of aluminum matrix composites with the support of robust st... more This work analyzes fatigue resistance of aluminum matrix composites with the support of robust statistics. The experimental samples studied were aluminum-based composites with a matrix containing Al, Cu and Mg and reinforced with diboride particles fabricated via both gravity and centrifugal casting. The variation in fatigue strength due to boron addition (forming diboride particles) was assessed via a comparison of the Paris equation exponent calculated for each composition as the slope of the da/dN vs ΔK curve plotted on a log-log scale. This approach, combined with the implementation of Kujawsky's crack driving force parameter and the application of robust statistics, allowed identifying variations in the crack growth behavior due to heterogeneities in the microstructure. The results showed that samples obtained via centrifugal casting have a higher fatigue resistance than those obtained via gravity casting. In addition, the analysis demonstrated how crack growth resistance decreased by increasing amounts of reinforcing particles in the material. The use of a robust statistics analysis was fundamental to avoid rejecting data from samples exhibiting variations in the crack growth curve. Keywords-Fatigue crack growth; robust statistics; aluminum matrix composites.

2021 ASEE Virtual Annual Conference Content Access, Jul 26, 2021

Thin Solid Films, 2019

This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

International Journal of Cast Metals Research, 2003

Late sulfur inoculation of spheroidal graphite cast irons. OM Suarez, RD Kendrick, CR Loper Inter... more Late sulfur inoculation of spheroidal graphite cast irons. OM Suarez, RD Kendrick, CR Loper International Journal of Cast Metals Research 16:11, 1-6, 2003. The addition of small amounts of sulfur in the form of pyrite granules to post-inoculated ductile irons was investigated. ...

MRS Advances, 2017

There is a need to expand the fundamental skills in science and engineering to include innovation…

Science and Engineering of Composite Materials, 2016

Porous recycled glass beds were produced for the potential use in water remediation. The present ... more Porous recycled glass beds were produced for the potential use in water remediation. The present work discusses the structural and mechanical characteristics of filters made of commercially available powdered recycled glass. The study measured the porosity and percolation performance of the sintered glass beds as a function of the sintering parameters and the particle size of the original powdered glass. Moreover, because TiO

Journal of Composite Materials, 2016

Bio-ferroelectric composites represent an inexpensive and environmentally friendly electronic alt... more Bio-ferroelectric composites represent an inexpensive and environmentally friendly electronic alternative for electrical applications such as capacitors, transistors, and actuators. The present research relates to the development of a biocomposite made of a chitosan–cellulose polymeric layer and bearing ferroelectric nanoparticles. The variables considered included the volume percentage of cellulose (15 v% and 25 v%) in the matrix and the amount of ferroelectric nanoparticles (0 wt.%, 10 wt.%, and 20 wt.%). Upon electrical characterization, the results indicated that the addition of the nanoparticles raised the capacitance and resistivity of the composite while the addition of cellulose lessened both electrical properties. The measured capacitance of the composites diminished as the applied voltage increased when contrasted with commercial capacitors where under similar testing conditions, as expected, the said capacity remained constant. Additionally, higher current flows were obta...

Advances in Applied Ceramics, 2014

The replacement of cement by mineral admixtures in concrete has been of increasing interest in th... more The replacement of cement by mineral admixtures in concrete has been of increasing interest in the construction industry. Nevertheless, several of the potential replacements, such as fly ash class F, lower the compressive strength of concrete at early age. This project investigates the use of nanosilica to compensate for such loss of compressive strength. A statistical experimental design involving mixtures of Portland cement, fly ash and nanosilica, in addition to water/binder ratio as an external factor, is proposed to study their combined effect on the compressive strength of concrete. This design allows estimating a cubic regression model that properly accounts for the effects of the mixture components within a constrained experimental region. The range of each factor was selected according to levels normally used in the industry. Finally, an optimisation strategy permits to recommend the use of nanosilica when high percentages of cement replacement by fly ash are present.

Science and Engineering of Composite Materials, 2009

An AI-Si-Sn alloy and an Al-B-Sn composite intended for bearing applications were manufactured by... more An AI-Si-Sn alloy and an Al-B-Sn composite intended for bearing applications were manufactured by centrifugal casting and their resulting tribological properties were compared. Microstructure gradients of silicon particles and boride dispersoids were observed on both materials, increasing from the internal to the external casting zones. Superficial hardness and pin-on-disk wear tests performed showed a higher hardness and lower wear coefficient in the external regions. The boride-reinforced composite exhibited lower wear and higher hardness than the aluminum-siliconbased alloy.

Science and Engineering of Composite Materials, 2012

The mechanical properties of centrifuged Al-Si-B composites containing aluminum diboride and alum... more The mechanical properties of centrifuged Al-Si-B composites containing aluminum diboride and aluminum dodecaboride particles were studied using optical and scanning electron microscopy (SEM), hardness tests, and nanoindentation. SEM was used to further analyze the Rockwell indentations, while nanoindentation experiments were completed on the matrix and the reinforcing particles. The outcomes of this study were compared with the results obtained in superfi cial Rockwell hardness and Vickers microhardness tests to determine which of the boride reinforcements was more benefi cial for the mechanical properties of the Al-Si matrix composite. Aluminum diboride was found to improve bulk mechanical properties more than did aluminum dodecaboride particles. On the other hand, aluminum dodecaboride showed to be a better reinforcement at the micron and submicron scales, as revealed by nanoindentation experiments. A discussion of these fi ndings helped understand the underlying mechanisms behind this apparent discrepancy.

Science and Engineering of Composite Materials, 2015

This study focuses on the fabrication of aluminum treated with nanocomposites made of aluminum an... more This study focuses on the fabrication of aluminum treated with nanocomposites made of aluminum and NbB

Science and Engineering of Composite Materials, 2014

An aluminum-copper matrix composite reinforced with aluminum diboride particles was studied at hi... more An aluminum-copper matrix composite reinforced with aluminum diboride particles was studied at high temperature via thermomechanometry experiments. The matrix contained 2 wt% Cu, whereas the amount of boron forming AlB2 ranged from 0 to 4 wt%, i.e., 0 to 8.31 vol% of diboride particles. In the first segment of the research, we demonstrated that larger amounts of AlB2 particles raised the composite hardness even at 300°C. To assess the material creep behavior, another set of specimens were tested under 1 N compression at 400°C and 500°C for 12 h. Higher levels of AlB2 allowed the composites to withstand compression creep deformations at those temperatures. By using existing creep models developed for metal matrix composites we were able to determine that viscous slip deformation was the dominant deformation mechanism for the temperatures and stress levels used in our experiments. Additionally, the computed creep activation energy for these aluminum matrix composites were found compar...

MRS Proceedings, 2011

ABSTRACTSince 2005, the University of Puerto Rico-Mayagüez (UPRM) has co-facilitated materials sc... more ABSTRACTSince 2005, the University of Puerto Rico-Mayagüez (UPRM) has co-facilitated materials science and engineering (MSE) clubs at low-income middle and high schools in Western Puerto Rico to increase awareness and interest in the areas of materials science, nanotechnology, and engineering. In this article, we describe the club activities and share the results of the 2009 end-of-year assessment regarding knowledge, interest, and educational aspirations in MSE, along with differences based on gender, parent education level, and school level. Overall, participants expressed positive opinions about engineering as a career. While students expressed high interest in pursuing university studies in science and engineering, some differences became apparent based on gender, parent education level, and school level. There were also differences between boys and girls in perceived knowledge gains. The results of this assessment provide promising evidence that school-based MSE clubs may help ...

Materials Science and Engineering: A, 2010

A series of Al-based composites with a matrix containing 2.5 wt.%Cu and 1 wt.%Mg, and reinforced ... more A series of Al-based composites with a matrix containing 2.5 wt.%Cu and 1 wt.%Mg, and reinforced with Al diborides was manufactured and characterized via microscopy and mechanical testing. The impact resistance of the composites revealed interaction between AlB 2 dispersoids and Mg originally present in the Al matrix. An unexpected increase in the absorbed impact energy of composites with diborides prompted complementary experiments leading to this finding. Hardness tests were correlated to those results and provided further evidence of the interaction between Mg and the dispersoids. Additional energy dispersive spectroscopy (EDS) analysis and X-ray diffraction tests supported with crystal modeling demonstrated that Mg effectively diffused into the AlB 2 crystal producing a doped structure with an Al 1−x Mg x B 2 formula where x lies between 0.08 and 0.15.