The aim of this work is to develop an automated laser processing process with high dimensional accuracy and predetermined process costs. This work includes analysis of size and cost prediction models for laser fabrication of internal Nd:YVO4 microchannels in PMMA and internal laser processing of polycarbonate for fabrication of microfluidic devices. To achieve these project goals, ANN and DoE compared the size and cost of CO2 and Nd:YVO4 laser systems. A complete implementation of feedback control with submicron accuracy of linear positioning with feedback from the encoder is implemented. In particular, automation of laser radiation and sample positioning is controlled by FPGA. In-depth knowledge of the Nd:YVO4 system operating procedures and software allowed the control unit to be replaced with a Compact-Rio Programmable Automation Controller (PAC), which was accomplished in the High Resolution Feedback 3D Positioning step of LabVIEW Code Control Submicron Encoders . Full automation of this process in LabVIEW code is in development. Current and future work includes measurements of dimensional accuracy, precision and reproducibility of design systems, and related optimization of microchannel geometry for microfluidic and laboratory device-on-a-chip fabrication for chemical/analytical applications and separation science.
Numerous applications of molded semi-hard metal (SSM) parts require excellent mechanical properties. Outstanding mechanical properties such as wear resistance, high strength and stiffness depend on the microstructure features created by the ultra-fine grain size. This grain size usually depends on the optimum processability of the SSM. However, SSM castings often contain residual porosity, which is extremely detrimental to performance. In this work, the important processes of molding semi-hard metals to obtain higher quality parts will be explored. These parts should have reduced porosity and improved microstructural characteristics, including ultra-fine grain size and uniform distribution of hardening precipitates and alloying microelement composition. In particular, the influence of the time-temperature pretreatment method on the development of the desired microstructure will be analyzed. Properties resulting from the improvement in mass, such as increases in strength, hardness and stiffness, will be investigated.
This work is a study of laser modification of the surface of H13 tool steel using a pulsed laser processing mode. The initial experimental screening plan carried out resulted in a more optimized detailed plan. A carbon dioxide (CO2) laser with a wavelength of 10.6 µm is used. In the experimental plan of the study, laser spots of three different sizes were used: 0.4, 0.2, and 0.09 mm in diameter. Other controllable parameters are laser peak power, pulse repetition rate and pulse overlap. Argon gas at a pressure of 0.1 MPa constantly helps laser processing. Sample H13 was roughened and chemically etched prior to processing to increase the surface absorptivity at the CO2 laser wavelength. Laser-treated samples were prepared for metallographic studies and their physical and mechanical properties were characterized. Metallographic studies and analyzes of the chemical composition were performed using scanning electron microscopy in combination with energy dispersive X-ray spectrometry. Crystallinity and phase detection of the modified surface was performed using an XRD system with Cu Kα radiation and a wavelength of 1.54 Å. The surface profile is measured using a stylus profiling system. The hardness properties of the modified surfaces were measured by Vickers diamond microindentation. The influence of surface roughness on the fatigue properties of the modified surfaces was studied using a specially manufactured thermal fatigue system. It has been observed that it is possible to obtain modified surface grains with ultrafine sizes of less than 500 nm. Improved surface depth in the range of 35 to 150 µm was achieved on laser treated H13 samples. The crystallinity of the modified H13 surface is significantly reduced, which is associated with a random distribution of crystallites after laser treatment. The minimum corrected average surface roughness of H13 Ra is 1.9 µm. Another important discovery is that the hardness of the modified H13 surface ranges from 728 to 905 HV0.1 at different laser settings. A relationship between thermal simulation results (heating and cooling rates) and hardness results was established to further understand the effect of laser parameters. These results are important for the development of surface hardening methods to improve wear resistance and heat-shielding coatings.
Parametric impact properties of solid sports balls in order to develop typical cores for GAA sliotar
The main goal of this study is to characterize the dynamic behavior of the sliotar core upon impact. The viscoelastic characteristics of the ball were performed for a range of impact velocities. Modern polymer spheres are sensitive to strain rate, while traditional multi-component spheres are strain dependent. The nonlinear viscoelastic response is defined by two stiffness values: initial stiffness and bulk stiffness. Traditional balls are 2.5 times stiffer than modern balls, depending on speed. The faster rate of increase in stiffness of conventional balls results in a more non-linear COR versus velocity compared to modern balls. The dynamic stiffness results show limited applicability of quasi-static tests and spring theory equations. An analysis of the behavior of spherical deformation shows that the displacement of the center of gravity and diametrical compression are not consistent for all types of spheres. Through extensive prototyping experiments, the effect of manufacturing conditions on ball performance was investigated. The production parameters of temperature, pressure and material composition varied to produce a range of balls. The hardness of the polymer affects the stiffness but not the energy dissipation, increasing the stiffness increases the stiffness of the ball. Nucleating additives affect the reactivity of the ball, an increase in the amount of additives leads to a decrease in the reactivity of the ball, but this effect is sensitive to the polymer grade. Numerical analysis was performed using three mathematical models to simulate the response of the ball to impact. The first model proved to be able to reproduce the behavior of the ball only to a limited extent, although it had previously been successfully used on other types of balls. The second model showed a reasonable representation of ball impact response that was generally applicable to all ball types tested, but the force-displacement response prediction accuracy was not as high as would be required for large-scale implementation. The third model showed significantly better accuracy when simulating ball response. The force values generated by the model for this model are 95% consistent with the experimental data.
This work achieved two main goals. One is the design and manufacture of a high-temperature capillary viscometer, and the second is semi-solid metal flow simulation to assist in design and provide data for comparison purposes. A high temperature capillary viscometer was built and used for initial testing. The device will be used to measure the viscosity of semi-hard metals under conditions of high temperatures and shear rates similar to those used in industry. The capillary viscometer is a single point system that can calculate viscosity by measuring the flow and pressure drop across the capillary, since viscosity is directly proportional to pressure drop and inversely proportional to flow. Design criteria include requirements for well-controlled temperatures up to 800ºC, injection shear rates above 10,000 s-1, and controlled injection profiles. A two-dimensional two-phase theoretical time-dependent model was developed using the FLUENT software for computational fluid dynamics (CFD). This has been used to evaluate the viscosity of semi-solid metals as they pass through a designed capillary viscometer at injection velocities of 0.075, 0.5 and 1 m/s. The effect of a fraction of metallic solids (fs) from 0.25 to 0.50 was also investigated. For the power-law viscosity equation used to develop the Fluent model, a strong correlation was noted between these parameters and the resulting viscosity.
This paper investigates the effect of process parameters on the production of Al-SiC metal matrix composites (MMC) in a batch composting process. Process parameters studied included stirrer speed, stirrer time, stirrer geometry, stirrer position, metallic liquid temperature (viscosity). Visual simulations were carried out at room temperature (25±C), computer simulations and verification tests for the production of MMC Al-SiC. In visual and computer simulations, water and glycerin/water were used to represent liquid and semi-solid aluminum, respectively. The effects of viscosities of 1, 300, 500, 800, and 1000 mPa s and stirring rates of 50, 100, 150, 200, 250, and 300 rpm were investigated. 10 rolls per piece. % reinforced SiC particles, similar to those used in aluminum MMK, were used in visualization and computational tests. Imaging tests were carried out in clear glass beakers. Computational simulations were performed using Fluent (CFD program) and the optional MixSim package. This includes 2D axisymmetric multiphase time-dependent simulation of production routes using the Eulerian (granular) model. The dependence of particle dispersion time, settling time and vortex height on the mixing geometry and the stirrer rotation speed has been established. For a stirrer with °at paddles, a paddle angle of 60 degrees has been found to be better suited to quickly obtain a uniform dispersion of particles. As a result of these tests, it was found that in order to obtain a uniform distribution of SiC, the stirring speed was 150 rpm for the water-SiC system and 300 rpm for the glycerol/water-SiC system. It was found that increasing the viscosity from 1 mPa·s (for liquid metal) to 300 mPa·s (for semi-solid metal) had a huge impact on the dispersion and deposition time of SiC. However, a further increase from 300 mPa·s to 1000 mPa·s has little effect on this time. A significant part of this work included the design, construction and validation of a dedicated rapid hardening casting machine for this high temperature treatment method. The machine consists of a stirrer with four flat blades at an angle of 60 degrees and a crucible in a furnace chamber with resistive heating. The installation includes an actuator that quickly extinguishes the processed mixture. This equipment is used for the production of Al-SiC composite materials. In general, good agreement was found between visualization, calculation and experimental test results.
There are many different rapid prototyping (RP) techniques that have been developed for large scale use mainly in the last decade. Rapid prototyping systems commercially available today use a variety of technologies using paper, wax, light-curing resins, polymers, and novel metal powders. The project included a rapid prototyping method, Fused Deposition Modeling, first commercialized in 1991. In this work, a new version of the system for modeling by surfacing using wax was developed and used. This project describes the basic design of the system and the wax deposition method. FDM machines create parts by extruding semi-molten material onto a platform in a predetermined pattern through heated nozzles. The extrusion nozzle is mounted on an XY table controlled by a computer system. In combination with automatic control of the plunger mechanism and the position of the depositor, accurate models are produced. Single layers of wax are stacked on top of each other to create 2D and 3D objects. The properties of the wax have also been analyzed to optimize the production process of the models. These include the phase transition temperature of the wax, the viscosity of the wax, and the shape of the wax drop during processing.
Over the past five years, research teams at the City University Dublin Division Science Cluster have developed two laser micromachining processes that can create channels and voxels with reproducible micron-scale resolution. The focus of this work is on the use of custom materials to isolate target biomolecules. Preliminary work demonstrates that new morphologies of capillary mixing and surface channels can be created to improve separation capabilities. This work will focus on the application of available micromachining tools to design surface geometries and channels that will provide improved separation and characterization of biological systems. The application of these systems will follow the lab-on-a-chip approach for biodiagnostic purposes. Devices made using this developed technology will be used in the microfluidic laboratory of the project on a chip. The goal of the project is to use experimental design, optimization, and simulation techniques to provide a direct relationship between laser processing parameters and micro- and nanoscale channel characteristics, and to use this information to improve separation channels in these microtechnologies. Specific outputs of the work include: channel design and surface morphology to improve separation science; monolithic stages of pumping and extraction in integrated chips; separation of selected and extracted target biomolecules on integrated chips.
Generation and control of temporal temperature gradients and longitudinal profiles along capillary LC columns using Peltier arrays and infrared thermography
A new direct contact platform for accurate temperature control of capillary columns has been developed based on the use of serially arranged individually controlled thermoelectric Peltier cells. The platform provides fast temperature control for capillary and micro LC columns and allows simultaneous programming of temporal and spatial temperatures. The platform operates over a temperature range of 15 to 200°C with a ramp rate of approximately 400°C/min for each of the 10 aligned Peltier cells. The system has been evaluated for several non-standard capillary-based measurement modes, such as the direct application of temperature gradients with linear and non-linear profiles, including static column temperature gradients and temporal temperature gradients, precise temperature controlled gradients, polymerized capillary monolithic stationary phases, and fabrication of monolithic phases in microfluidic channels (on a chip). The instrument can be used with standard and column chromatography systems.
Electrohydrodynamic focusing in a two-dimensional planar microfluidic device for preconcentration of small analytes
This work includes electrohydrodynamic focusing (EHDF) and photon transfer to aid in the development of pre-enrichment and species identification. EHDF is an ion-balanced focusing method based on establishing a balance between hydrodynamic and electrical forces, in which the ions of interest become stationary. This study presents a novel method using a 2D open 2D flat space planar microfluidic device instead of the conventional microchannel system. Such devices can preconcentrate large amounts of substances and are relatively easy to manufacture. This study presents the results of a newly developed simulation using COMSOL Multiphysics® 3.5a. The results of these models were compared with experimental results to test the identified flow geometries and areas of high concentration. The developed numerical microfluidic model was compared with previously published experiments and the results were very consistent. Based on these simulations, a new type of ship was researched to provide optimal conditions for the EHDF. Experimental results using the chip outperformed the performance of the model. In the fabricated microfluidic chips, a new mode was observed, called lateral EGDP, when the substance under study was focused perpendicular to the applied voltage. Because detection and imaging are key aspects of such pre-enrichment and species identification systems. Numerical models and experimental verification of light propagation and light intensity distribution in two-dimensional microfluidic systems are presented. The developed numerical model of light propagation was successfully verified experimentally both in terms of the actual path of light through the system and in terms of intensity distribution, which gave results that may be of interest for optimizing photopolymerization systems, as well as for optical detection systems using capillaries. .
Depending on the geometry, microstructures can be used in telecommunications, microfluidics, microsensors, data warehousing, glass cutting, and decorative marking. In this work, the relationship between the settings of the parameters of the Nd:YVO4 and CO2 laser system and the size and morphology of microstructures was investigated. The studied parameters of the laser system include power P, pulse repetition rate PRF, number of pulses N and scan rate U. Measured output dimensions include equivalent voxel diameters as well as microchannel width, depth and surface roughness. A 3D micromachining system was developed using a Nd:YVO4 laser (2.5 W, 1.604 µm, 80 ns) to fabricate microstructures inside polycarbonate specimens. Microstructural voxels have a diameter of 48 to 181 µm. The system also provides precise focusing by using microscope objectives to create smaller voxels in the 5 to 10 µm range in soda-lime glass, fused silica and sapphire samples. A CO2 laser (1.5 kW, 10.6 µm, minimum pulse duration 26 µs) was used to create microchannels in the soda-lime glass samples. The cross-sectional shape of the microchannels varied widely between v-grooves, u-grooves, and superficial ablation sites. The sizes of microchannels also vary greatly: from 81 to 365 µm wide, from 3 to 379 µm in depth, and surface roughness from 2 to 13 µm, depending on the installation. Microchannel sizes were examined according to laser processing parameters using response surface methodology (RSM) and design of experiments (DOE). The collected results were used to study the effect of process parameters on the volumetric and mass ablation rate. In addition, a thermal process mathematical model has been developed to help understand the process and allow the channel topology to be predicted prior to actual fabrication.
The metrology industry is always looking for new ways to accurately and quickly explore and digitize surface topography, including calculating surface roughness parameters and creating point clouds (sets of three-dimensional points describing one or more surfaces) for modeling or reverse engineering. systems exist, and optical systems have grown in popularity over the past decade, but most optical profilers are expensive to purchase and maintain. Depending on the type of system, optical profilers can also be difficult to design and their fragility may not be suitable for most shop or factory applications. This project covers the development of a profiler using the principles of optical triangulation. The developed system has a scanning table area of 200 x 120 mm and a vertical measurement range of 5 mm. The position of the laser sensor above the target surface is also adjustable by 15 mm. A control program was developed for automatic scanning of user-selected parts and surface areas. This new system is characterized by dimensional accuracy. The measured maximum cosine error of the system is 0.07°. The dynamic accuracy of the system is measured at 2 µm in the Z-axis (height) and about 10 µm in the X and Y axes. The size ratio between the scanned parts (coins, screws, washers and fiber lens dies) was good. System testing will also be discussed, including profiler limitations and possible system improvements.
The aim of this project is to develop and characterize a new optical high-speed online system for surface defects inspection. The control system is based on the principle of optical triangulation and provides a non-contact method for determining the three-dimensional profile of diffuse surfaces. The main components of the development system include a diode laser, a CCf15 CMOS camera, and two PC-controlled servo motors. Sample movement, image capture, and 3D surface profiling are programmed in LabView software. Checking the captured data can be facilitated by creating a program for virtual rendering of a 3D scanned surface and calculating the required surface roughness parameters. Servo motors are used to move the sample in the X and Y directions with a resolution of 0.05 µm. The developed non-contact online surface profiler can perform fast scanning and high resolution surface inspection. The developed system is successfully used to create automatic 2D surface profiles, 3D surface profiles and surface roughness measurements on the surface of various sample materials. The automated inspection equipment has an XY scanning area of 12 x 12 mm. To characterize and calibrate the developed profiling system, the surface profile measured by the system was compared with the same surface measured using an optical microscope, binocular microscope, AFM and Mitutoyo Surftest-402.
The requirements for the quality of products and the materials used in them are becoming more and more demanding. The solution to many visual quality assurance (QA) problems is the use of real-time automated surface inspection systems. This requires a uniform product quality at a high throughput. Therefore, systems are needed that are 100% capable of testing materials and surfaces in real time. To achieve this goal, the combination of laser technology and computer control technology provides an effective solution. In this work, a high-speed, low-cost, and high-precision non-contact laser scanning system was developed. The system is able to measure the thickness of solid opaque objects using the principle of laser optical triangulation. The developed system ensures the accuracy and reproducibility of measurements at the micrometer level.
The aim of this project is to design and develop a laser inspection system for surface defect detection and evaluate its potential for high speed inline applications. The main components of the detection system are a laser diode module as an illumination source, a CMOS random access camera as a detection unit, and an XYZ translation stage. Algorithms for analyzing data obtained by scanning various sample surfaces were developed. The control system is based on the principle of optical triangulation. The laser beam is incident obliquely on the sample surface. The difference in surface height is then taken as the horizontal movement of the laser spot over the sample surface. This allows height measurements to be taken using the triangulation method. The developed detection system is first calibrated to obtain a conversion factor that will reflect the relationship between the displacement of the point measured by the sensor and the vertical displacement of the surface. The experiments were carried out on different surfaces of the sample materials: brass, aluminum and stainless steel. The developed system is able to accurately generate a 3D topographic map of defects that occur during operation. A spatial resolution of about 70 µm and a depth resolution of 60 µm were achieved. System performance is also verified by measuring the accuracy of measured distances.
High-speed fiber laser scanning systems are used in automated industrial manufacturing environments to detect surface defects. More modern methods for detecting surface defects include the use of optical fibers for illumination and component detection. This dissertation includes the design and development of a new high-speed optoelectronic system. In this paper, two sources of LEDs, LEDs (light emitting diodes) and laser diodes, are investigated. A row of five emitting diodes and five receiving photodiodes is located opposite each other. The data collection is controlled and analyzed by a PC using the LabVIEW software. The system is used to measure the dimensions of surface defects such as holes (1 mm), blind holes (2 mm) and notches in various materials. The results show that while the system is primarily intended for 2D scanning, it can also operate as a limited 3D imaging system. The system also showed that all metallic materials studied were capable of reflecting infrared signals. A newly developed method using an array of inclined fibers allows the system to achieve adjustable resolution with a maximum system resolution of approximately 100 µm (collecting fiber diameter). The system has been successfully used to measure surface profile, surface roughness, thickness and reflectivity of various materials. Aluminum, stainless steel, brass, copper, tuffnol and polycarbonate can be tested with this system. The advantages of this new system are faster detection, lower cost, smaller size, higher resolution and flexibility.
Design, build and test new systems to integrate and deploy new environmental sensor technologies. Particularly suitable for faecal bacteria monitoring applications
Modifying the Micro-Nano Structure of Silicon Solar PV Panels to Improve Energy Supply
One of the major engineering challenges facing global society today is sustainable energy supply. It’s time for society to start relying heavily on renewable energy sources. The sun provides the earth with free energy, but modern methods of using this energy in the form of electricity have some limitations. In the case of photovoltaic cells, the main problem is the insufficient efficiency of collecting solar energy. Laser micromachining is commonly used to create interconnects between photovoltaic active layers such as glass substrates, hydrogenated silicon, and zinc oxide layers. It is also known that more energy can be obtained by increasing the surface area of a solar cell, for example by micromachining. It has been shown that nanoscale surface profile details affect the energy absorption efficiency of solar cells. The purpose of this paper is to investigate the benefits of adapting micro-, nano- and mesoscale solar cell structures to provide higher power. Varying the technological parameters of such microstructures and nanostructures will make it possible to study their influence on the surface topology. Cells will be tested for the energy they produce when exposed to experimentally controlled levels of electromagnetic light. A direct relationship will be established between cell efficiency and surface texture.
Metal Matrix Composites (MMCs) are rapidly becoming prime candidates for the role of structural materials in engineering and electronics. Aluminum (Al) and copper (Cu) reinforced with SiC due to their excellent thermal properties (eg low thermal expansion coefficient (CTE), high thermal conductivity) and improved mechanical properties (eg higher specific strength, better performance). It is widely used in various industries for wear resistance and specific modulus. Recently, these high ceramic MMCs have become another trend for temperature control applications in electronic packages. Typically, in power device packages, aluminum (Al) or copper (Cu) is used as a heatsink or base plate to connect to the ceramic substrate that carries the chip and associated pin structures. The large difference in coefficient of thermal expansion (CTE) between ceramic and aluminum or copper is disadvantageous because it reduces the reliability of the package and also limits the size of the ceramic substrate that can be attached to the substrate.
Given this shortcoming, it is now possible to develop, investigate and characterize new materials that meet these requirements for thermally improved materials. With improved thermal conductivity and coefficient of thermal expansion (CTE) properties, MMC CuSiC and AlSiC are now viable solutions for electronics packaging. This work will evaluate the unique thermophysical properties of these MMCs and their possible applications for thermal management of electronic packages.
Oil companies experience significant corrosion in the welding zone of oil and gas industry systems made of carbon and low alloy steels. In environments containing CO2, corrosion damage is usually attributed to differences in the strength of protective corrosion films deposited on various carbon steel microstructures. Local corrosion in the weld metal (WM) and heat-affected zone (HAZ) is mainly due to galvanic effects due to differences in alloy composition and microstructure. Base metal (PM), WM, and HAZ microstructural characteristics were investigated to understand the effect of microstructure on the corrosion behavior of mild steel welded joints. Corrosion tests were carried out in a 3.5% NaCl solution saturated with CO2 under deoxygenated conditions at room temperature (20±2°C) and pH 4.0±0.3. Characterization of corrosion behavior was carried out using electrochemical methods for determining the open circuit potential, potentiodynamic scanning and linear polarization resistance, as well as general metallographic characterization using optical microscopy. The main morphological phases detected are acicular ferrite, retained austenite, and martensitic-bainitic structure in WM. They are less common in HAZ. Significantly different electrochemical behavior and corrosion rates were found in PM, VM and HAZ.
The work covered by this project is aimed at improving the electrical efficiency of submersible pumps. The demands on the pump industry to move in this direction have recently increased with the introduction of new EU legislation requiring the industry as a whole to achieve new and higher levels of efficiency. This paper analyzes the use of a cooling jacket to cool the pump solenoid area and proposes design improvements. In particular, the fluid flow and heat transfer in the cooling jackets of operating pumps are characterized. Improvements in jacket design will provide better heat transfer to the pump motor area resulting in improved pump efficiency while reducing induced drag. For this work, a dry pit mounted pump test system was added to the existing 250 m3 test tank. This allows high-speed camera tracking of the flow field and a thermal image of the pump casing. The flow field validated by CFD analysis allows experimentation, testing and comparison of alternative designs to keep operating temperatures as low as possible. The original design of the M60-4 pole pump withstood a maximum external pump casing temperature of 45°C and a maximum stator temperature of 90°C. Analysis of various model designs shows which designs are more useful for more efficient systems and which should not be used. In particular, the design of the integrated cooling coil has no improvement over the original design. Increasing the number of impeller blades from four to eight reduced the operating temperature measured at the casing by seven degrees Celsius.
The combination of high power density and reduced exposure time in metal processing results in a change in the surface microstructure. Obtaining the optimal combination of laser process parameters and cooling rate is critical to changing the grain structure and improving the tribological properties at the material surface. The main goal of this study was to investigate the effect of fast pulsed laser processing on the tribological properties of commercially available metallic biomaterials. This work is devoted to laser surface modification of stainless steel AISI 316L and Ti-6Al-4V. A 1.5 kW pulsed CO2 laser was used to study the influence of various laser process parameters and the resulting surface microstructure and morphology. Using a cylindrical sample rotated perpendicular to the laser radiation direction, the laser radiation intensity, exposure time, energy flux density, and pulse width were varied. Characterization was performed using SEM, EDX, needle roughness measurements and XRD analysis. A surface temperature prediction model was also implemented to set the initial parameters of the experimental process. Process mapping was then carried out to determine a number of specific parameters for laser treatment of the surface of the molten steel. There is a strong correlation between illuminance, exposure time, processing depth and roughness of the processed sample. Increased depth and roughness of microstructural changes were associated with higher exposure levels and exposure times. By analyzing the roughness and depth of the treated area, energy fluence and surface temperature models are used to predict the degree of melting that will occur on the surface. As the interaction time of the laser beam increases, the surface roughness of the steel increases for various studied pulse energy levels. While the surface structure was observed to retain the normal alignment of the crystals, changes in grain orientation were observed in the laser treated areas.
Analysis and characterization of tissue stress behavior and its implications for scaffold design
In this project, several different scaffold geometries were developed and finite element analysis was performed to understand the mechanical properties of the bone structure, their role in tissue development, and the maximum distribution of stress and strain in the scaffold. Computed tomography (CT) scans of trabecular bone samples were collected in addition to scaffold structures designed with CAD. These designs allow you to create and test prototypes, as well as perform FEM of these designs. Mechanical measurements of microdeformations were performed on fabricated scaffolds and trabecular specimens of the femoral head bone and these results were compared with those obtained by the FEA for the same structures. It is believed that mechanical properties depend on the designed pore shape (structure), pore size (120, 340 and 600 µm) and loading conditions (with or without loading blocks). Changes in these parameters were investigated for porous frameworks of 8 mm3, 22.7 mm3 and 1000 mm3 in order to comprehensively study their effect on stress distribution. The results of experiments and simulations show that the geometric design of the structure plays an important role in the distribution of stress, and highlight the great potential of the framework design to improve bone regeneration. Generally, pore size is more important than porosity level in determining the overall maximum stress level. However, the level of porosity is also important in determining the osteoconductivity of scaffold structures. As the porosity level increases from 30% to 70%, the maximum stress value increases significantly for the same pore size.
The pore size of the scaffold is also important to the fabrication method. All modern methods of rapid prototyping have certain limitations. While conventional fabrication is more versatile, more complex and smaller designs are often impossible to fabricate. Most of these technologies are currently nominally unable to sustainably produce pores below 500 µm. Thus, the results with a pore size of 600 µm in this work are most relevant to the production capabilities of current rapid manufacturing technologies. The presented hexagonal structure, although considered only in one direction, would be the most anisotropic structure compared to the structures based on the cube and triangle. Cubic and triangular structures are relatively isotropic compared to hexagonal structures. Anisotropy is important when considering the osteoconductivity of the designed scaffold. Stress distribution and aperture location affect the remodeling process, and different loading conditions can change the maximum stress value and its location. The predominant loading direction should promote pore size and distribution to allow cells to grow into larger pores and provide nutrients and building materials. Another interesting conclusion of this work, by examining the distribution of stress in the cross section of the pillars, is that higher stress values are recorded at the surface of the pillars compared to the center. In this work, it was shown that the pore size, porosity level, and loading method are closely related to the stress levels experienced in the structure. These findings demonstrate the possibility of creating strut structures in which stress levels on the strut surface can vary to a greater extent, which can promote cell attachment and growth.
Synthetic bone substitute scaffolds offer the opportunity to individually tailor properties, overcome limited donor availability, and improve osseointegration. Bone engineering aims to address these issues by providing high quality grafts that can be supplied in large quantities. In these applications, both the internal and external scaffold geometry are of great importance, as they have a significant impact on the mechanical properties, permeability, and cell proliferation. Rapid prototyping technology allows the use of non-standard materials with a given and optimized geometry, manufactured with high precision. This paper explores the ability of 3D printing techniques to fabricate complex geometries of skeletal scaffolds using biocompatible calcium phosphate materials. Preliminary studies of the proprietary material show that the predicted directional mechanical behavior can be achieved. Actual measurements of the directional mechanical properties of the fabricated samples showed the same trends as the results of finite element analysis (FEM). This work also demonstrates the feasibility of 3D printing to fabricate tissue engineering geometry scaffolds from a biocompatible calcium phosphate cement. The frameworks were made by printing with an aqueous solution of disodium hydrogen phosphate on a powder layer consisting of a homogeneous mixture of calcium hydrogen phosphate and calcium hydroxide. The wet chemical deposition reaction takes place in the powder bed of the 3D printer. Solid samples were made to measure the mechanical properties of the volumetric compression of the manufactured calcium phosphate cement (CPC). The parts thus produced had an average modulus of elasticity of 3.59 MPa and an average compressive strength of 0.147 MPa. Sintering leads to a significant increase in compression properties (E = 9.15 MPa, σt = 0.483 MPa), but reduces the specific surface area of the material. As a result of sintering, calcium phosphate cement decomposes into β-tricalcium phosphate (β-TCP) and hydroxyapatite (HA), which is confirmed by the data of thermogravimetric and differential thermal analysis (TGA/DTA) and X-ray diffraction analysis (XRD). properties are insufficient for highly loaded implants, where the required strength is from 1.5 to 150 MPa, and the compressive rigidity exceeds 10 MPa. However, further post-processing, such as infiltration with biodegradable polymers, can make these structures suitable for stent applications.
Objective: Research in soil mechanics has shown that vibration applied to aggregates results in more efficient particle alignment and a reduction in the energy required to act on the aggregate. Our goal was to develop a method for the impact of vibration on the bone impaction process and evaluate its effect on the mechanical properties of impacted grafts.
Phase 1: Milling of 80 heads of bovine femur using a Noviomagus bone mill. The grafts were then washed using a pulsed saline wash system on a sieve tray. A vibro-impact device was developed, equipped with two 15 V DC motors with eccentric weights fixed inside a metal cylinder. Throw a weight on it from a given height 72 times to reproduce the process of hitting a bone. The vibration frequency range measured with an accelerometer installed in the vibration chamber was tested. Each shear test was then repeated at four different normal loads to obtain a series of stress-strain curves. Mohr-Coulomb failure envelopes were constructed for each test, from which shear strength and blocking values were derived.
Phase 2: Repeat the experiment by adding blood to replicate the rich environment encountered in surgical settings.
Stage 1: Grafts with increased vibration at all frequencies of vibration showed higher shear strength compared to impact without vibration. Vibration at 60 Hz had the greatest impact and was significant.
Stage 2: Grafting with additional vibratory impact in saturated aggregates showed lower shear strength for all normal compressive loads than impact without vibration.
Conclusion: The principles of civil engineering are applicable to the implantation of the implanted bone. In dry aggregates, the addition of vibration can improve the mechanical properties of the impact particles. In our system, the optimal vibration frequency is 60 Hz. In saturated aggregates, an increase in vibration adversely affects the shear strength of the aggregate. This can be explained by the liquefaction process.
The aim of this work was to design, build and test a system that can disturb the subjects standing on it in order to assess their ability to respond to these changes. This can be done by quickly tilting the surface on which the person is standing and then returning it to a horizontal position. From this it is possible to determine whether the subjects were able to maintain a state of equilibrium and how long it took them to restore this state of equilibrium. This state of equilibrium will be determined by measuring the subject’s postural influence. Their natural postural sway was measured with a foot pressure profile panel to determine how much the sway was during the test. The system is also designed to be more versatile and affordable than currently commercially available because, while these machines are important for research, they are not currently widely used due to their high cost. The newly developed system presented in this article has been used to move test objects weighing up to 100 kg.
In this work, six laboratory experiments in engineering and physical sciences were designed to improve the learning process for students. This is achieved by installing and creating virtual instruments for these experiments. The use of virtual instruments is compared directly with traditional laboratory teaching methods, and the basis for the development of both approaches is discussed. Previous work using computer-assisted learning (CBL) in similar projects related to this work has been used to evaluate some of the benefits of virtual instruments, especially those related to increased student interest, memory retention, comprehension, and ultimately lab reporting. . related benefits. The virtual experiment discussed in this study is a revised version of the traditional style experiment and thus provides a direct comparison of the new CBL technique with the traditional style lab. There is no conceptual difference between the two versions of the experiment, the only difference is in the way it is presented. The effectiveness of these CBL methods was assessed by observing the performance of students using the virtual instrument compared to other students in the same class performing the traditional experimental mode. All students are assessed by submitting reports, multiple choice questions related to their experiments and questionnaires. The results of this study were also compared with other related studies in the field of CBL.
Post time: Feb-19-2023