Fabrico e caracterização mecânica de placas estabilizadoras de fraturas em material compósito polimérico

Mestrado de dupla diplomação com a UTFPR - Universidade Tecnológica Federal do ParanáFraturas são eventos com altíssima ocorrência e que, além dos impactos na qualidade de vida, geram enormes gastos por todo o mundo. Para auxiliar nos processos de consolidação óssea após um destes incidentes, são utilizadas placas estabilizadoras de fratura, normalmente, fabricadas em materiais metálicos. Contudo, estes materiais apresentam algumas desvantagens, tais como os efeitos adversos provocados pela corrosão, as falhas por fadiga, as reações alérgicas, o custo, considerado alto e, principalmente, o fenômeno da blindagem óssea: uma redução na densidade dos ossos devido à alta rigidez do implante. Visando contornar tais problemas, o objetivo deste estudo foi fabricar e caracterizar placas estabilizadoras de fratura em material compósito de resina poliuretana (PU) reforçada com fibra de vidro. Para tal, foram concebidas e simuladas diferentes geometrias; o material foi avaliado em tração e, posteriormente, os implantes na flexão em 4 pontos. As simulações numéricas não mostraram diferenças significativas nas propriedades em flexão dos diferentes modelos avaliados, desta forma, o modelo mais utilizado atualmente foi adaptado para o fabrico em compósito. Em tração, a resina PU utilizada demostrou aumento de 102% na tensão máxima atingida quando se empregou 15 Wf% de reforços. Nas placas, a inserção de reforços entre 10 a 25% também aumentou a rigidez estrutural em 126-165%, comparativamente com as amostras de PU pura. Por outro lado, alterações no número de furos, de 4 para 6, reduziram a tensão máxima atingida em 40%. Quanto ao processo utilizado, este apresentou baixo custo, foi altamente customizável e permitiu o desenvolvimento de geometrias complexas. Desta forma, mesmo que os valores de resistência e rigidez ainda precisem aumentar para utilização segura quando implantado, os métodos adotados mostraram-se uma alternativa efetiva para o fabrico e caracterização deste tipo de dispositivo.Fractures are events with a very high occurrence that, besides the impact caused to the wellness, it also generates huge expenses all over the world. To assist the bone healing processes after one of these incidents, osteosynthesis plates, usually manufactured with metallic materials, are used. However, these materials have some disadvantages, such as adverse effects caused by corrosion, fatigue failures, allergic reactions, high cost and, mainly, the stress shielding phenomenon: a reduction in bone density due to the high implant stiffness. To avoid these problems, this study aims to manufacture and characterize fracture osteosynthesis plates, made with glass fiber reinforced polyurethane composite. For this, three different geometries were designed and simulated; the material was evaluated in tensile tests and, subsequently, the implants were submitted to 4-point bending. Finite Element Simulations did not show significant differences in the flexural properties of the evaluated models, thus, the most modern one was adapted to be manufactured using composite. The maximum stress reached by the samples in tensile test, increased 102% when 15% of reinforcements were used. In the plates, fiber reinforcements between 10 and 25% also increased the structural stiffness by 126-165%, when compared to pure polyurethane. On the other hand, changes in the number of holes, from 4 to 6, reduced the maximum stress by 40%. Regarding to the manufacturing process used, it was low cost, highly customizable and allowed the development of complex geometries. Thus, even though the values of strength and stiffness still need to be increased for safe implanted use, the methods adopted have proved to be an effective alternative for the manufacture of bone plates

Low-cost multifunctional vacuum chamber for manufacturing PDMS based composites

Polydimethylsiloxane (PDMS) is one of the best known elastomers and has been used in several areas of activity, due to its excellent characteristics and properties, such as biocompatibility, flexibility, optical transparency and chemical stability. Furthermore, PDMS modified with other materials promotes the desired changes to broaden its range of applications in various fields of science. However, the heating, mixing and degassing steps of the manufacturing process have not received much attention in recent years when it comes to blending with solid materials. For instance, PDMS has been extensively studied in combination with waxes, which are frequently in a solid state at room temperature and as a result the interaction and manufacturing process are extremely complex and can compromise the desired material. Thus, in this work it is proposed a multifunctional vacuum chamber (MVC) with the aim to improve and accelerate the manufacturing process of PDMS composites combined with additives, blends and different kinds of solid materials. The MVC developed in this work allows to control the mixing speed parameters, temperature control and internal pressure. In addition, it is a low cost equipment and can be used for other possible modifications with different materials and processes with the ability to control those parameters. As a result, samples fabricated by using the MVC can achieve a time improvement over 133% at the heating and mixing step and approximately 200% at the last degassing step. Regarding the complete manufacturing process, it is possible to achieve an improvement over 150%, when compared with the conventional manufacturing process. When compared to maximum tensile strength, specimens manufactured using the MVC have shown a 39% and 65% improvement in maximum strain. The samples have also shown a 9% improvement in transparency at room temperature and 12% at a temperature of about 75 C. It should be noted that the proposed MVC can be used for other blends and manufacturing processes where it is desirable to control the temperature, agitation speed and pressure.This research was partially funded by Portuguese national funds of FCT/MCTES (PIDDAC) through the base funding from the following research units: UIDB/00690/2020 (CIMO) and UIDB/04077/2020 (MEtRICs). The authors are grateful for the funding of ANI, FCT and CIMO through the projects POCI-01-02B7-FEDER-069844, and EXPL2021CIMO_01, respectively. The authors are also grateful for the partial funding of FCT through the projects EXPL/EMEEME/ 0732/2021, NORTE-01-0145-FEDER-030171 (PTDC/EMD-EMD/30171/2017) funded by COMPETE2020, NORTE2020, PORTUGAL2020, and FEDER.info:eu-repo/semantics/publishedVersio

Mechanical characterization of PDMS with different mixing ratios

Polydimethylsiloxane (PDMS) is a transparent, biocompatible, flexible, simple processing, chemically and thermally stable polymer that has been attracting attention due to its wide range of applications in mechanical, civil and electronic engineering and biomedical field. In order to improve PDMS’ properties, many studies have been investigating the effect of the mixing ratios of its components (base polymer and curing agent) on the mechanical properties, once they affect the number of interactions between the polymer chains of the material. With the aim to make a comparison of the mechanical response of pure PDMS (SYLGARD 184) with different ratios of the base elastomer and the curing agent, tensile and hardness tests were performed. The tested mixing ratios were 10:1, 10:2 and 10:3 (base: curing agent). Tensile tests were executed in a universal tester machine, set up with a velocity of 500 mm/min and pre-load of 1 N. An analogical portable durometer type Shore A was used to carry out the hardness test, according to ASTM D2240. The results for the tensile test showed that an increase in the amount of cure agent reduced the tensile strength. The hardness values obtained were 41.7±0.95, 43.2±1.03 and 37.2±1.14 Shore A for pure PDMS with ratios equal to 10:1, 10:2 and 10:3, respectively.This research was partially funded through the base funding from the following research units: UIDB/00690/2020 (CIMO).info:eu-repo/semantics/publishedVersio

Low-cost multifunctional vacuum chamber for manufacturing PDMS based composites

Polydimethylsiloxane (PDMS) is one of the best known elastomers and has been used in several areas of activity, due to its excellent characteristics and properties, such as biocompatibility, flexibility, optical transparency and chemical stability. Furthermore, PDMS modified with other materials promotes the desired changes to broaden its range of applications in various fields of science. However, the heating, mixing and degassing steps of the manufacturing process have not received much attention in recent years when it comes to blending with solid materials. For instance, PDMS has been extensively studied in combination with waxes, which are frequently in a solid state at room temperature and as a result the interaction and manufacturing process are extremely complex and can compromise the desired material. Thus, in this work it is proposed a multifunctional vacuum chamber (MVC) with the aim to improve and accelerate the manufacturing process of PDMS composites combined with additives, blends and different kinds of solid materials. The MVC developed in this work allows to control the mixing speed parameters, temperature control and internal pressure. In addition, it is a low cost equipment and can be used for other possible modifications with different materials and processes with the ability to control those parameters. As a result, samples fabricated by using the MVC can achieve a time improvement over 133% at the heating and mixing step and approximately 200% at the last degassing step. Regarding the complete manufacturing process, it is possible to achieve an improvement over 150%, when compared with the conventional manufacturing process. When compared to maximum tensile strength, specimens manufactured using the MVC have shown a 39% and 65% improvement in maximum strain. The samples have also shown a 9% improvement in transparency at room temperature and 12% at a temperature of about 75 °C. It should be noted that the proposed MVC can be used for other blends and manufacturing processes where it is desirable to control the temperature, agitation speed and pressure.This research was partially funded by Portuguese national funds of FCT/MCTES (PIDDAC) through the base funding from the following research units: UIDB/00690/2020 (CIMO) and UIDB/04077/2020 (MEtRICs). The authors are grateful for the funding of ANI, FCT and CIMO through the projects POCI-01-02B7-FEDER-069844, and EXPL2021CIMO_01, respectively. The authors are also grateful for the partial funding of FCT through the projects EXPL/EMEEME/0732/2021, NORTE-01-0145-FEDER-030171 (PTDC/EMD-EMD/30171/2017) funded by COMPETE2020, NORTE2020, PORTUGAL2020, and FEDER

Stress Concentration on PDMS: An evaluation of three numerical constitutive models using digital image correlation

The examination of hyperelastic materials’ behavior, such as polydimethylsiloxane (PDMS), is crucial for applications in areas as biomedicine and electronics. However, the limitations of hyperelastic models for specific stress scenarios, with stress concentration, are not well explored on the literature. To address this, firstly, three constitutive models were evaluated (Neo-Hookean, Mooney-Rivlin, and Ogden) using numerical simulations and Digital Image Correlation (DIC) analysis during a uniaxial tensile test. The samples were made of PDMS with stress concentration geometries (center holes, shoulder fillets, and edge notches). Results of ANOVA analysis showed that any of the three models can be chosen for numerical analysis of PDMS since no significant differences in suitability were found. Finally, the Ogen model was chosen to obtain the stress concentration factors for these geometries, a property which characterize how discontinuities change the maximum stress supported by an element. Our study provides new values for variables needed to analyze and design hyperelastic elements and produce a foundation for understanding PDMS stress-strain behavior.The authors acknowledge the projects EXPL/EME-EME/0732/2021 and 2022.06207.PTDC for the financial support, through national funds (OE), within the scope of the Scientific Research and Technological Development Projects (IC&DT) program in all scientific domains (PTDC), PORTUGAL 2020 Partnership Agreement, European Regional Development Fund (FEDER), via the Foundation for Science and Technology, I.P. (FCT, I.P) and the R&D Units projects (UIDB/00690/2020 and UIDP/00690/2020) (CIMO), SusTEC (LA/P/0007/2020), UIDB/ 04077/2020, UIDP/04077/2020, UIDB/04436/2020 and UIDB/00532/ 2020. Andrews Souza acknowledges FCT for the Ph.D. scholarship 2021.07961.BD.info:eu-repo/semantics/publishedVersio

PU tensile tests: conventional and digital image correlation analysis

Polyurethane (PU) is a polymer, used as coating, paint, foam, adhesive, and even in biomedical devices. To furthermore expand its applications, it can be combined with additives such as Calcium Carbonate (CaCO3), an inexpensive material, widely available in nature, or with fibers, such as glass fibers explored in several sectors, likewise the aerospace and automobile industries. To determine the mechanical properties of these materials, the tensile test is the most used due to its great ease of application and flexibility. However, conventional processes, such as the use of strain gauges or crosshead displacement data, may not provide detailed information about the strain field, or cannot be able to evaluate the Poisson's ratio and the true stresses for the entire stressstrain curve. Thus, digital image correlation (DIC) methods are a promising alternative, consisting of strain field measurement without contact with the surface of the structure. In this context, this study carried out the tensile characterization of two main polyurethane samples: one petrochemical, distributed by Sika (R), reinforced with type E glass fiber: and the other, natural, manufactured by Kehl (R) from castor oils, and combined with CaCO3 particles. During the tests, DIC was applied to evaluate the Poisson's ratio and, subsequently, Scanning Electron Microscopy (SEM) analyses were performed, revealing a higher number of bubbles on Sika's polymer, which contributes to the reduction of the maximum supported stresses, since these pores, with dimensions of up to 25 hm, were regions where the cracks started and headed the breakage. Poisson's ratios were all around 0.4 and the highest tensile strength values were obtained from E-glass reinforced samples (TS015), around 117.24 +/- 13.20MPa. CaCO3 particles also acted as reinforced, increasing maximum stress reached from 20MPa to values between 29 and 37MPa.This research was partially funded through the base funding from the following research units: UIDB/00690/2020 (CIMO).info:eu-repo/semantics/publishedVersio

Composite material of PDMS with interchangeable transmittance: study of optical, mechanical properties and wettability

Polydimethylsiloxane (PDMS) is a polymer that has attracted the attention of researchers due to its unique properties such as transparency, biocompatibility, high flexibility, and physical and chemical stability. In addition, PDMS modification and combination with other materials can expand its range of applications. For instance, the ability to perform superhydrophobic coating allows for the manufacture of lenses. However, many of these processes are complex and expensive. One of the most promising modifications, which consists of the development of an interchangeable coating, capable of changing its optical characteristics according to some stimuli, has been underexplored. Thus, we report an experimental study of the mechanical and optical properties and wettability of pure PDMS and of two PDMS composites with the addition of 1% paraffin or beeswax using a gravity casting process. The composites’ tensile strength and hardness were lower when compared with pure PDMS. However, the contact angle was increased, reaching the highest values when using the paraffin additive. Additionally, these composites have shown interesting results for the spectrophotometry tests, i.e., the material changed its optical characteristics when heated, going from opaque at room temperature to transparent, with transmittance around 75%, at 70 °C. As a result, these materials have great potential for use in smart devices, such as sensors, due to its ability to change its transparency at high temperatures.This research was partially funded by Portuguese national funds of FCT/MCTES (PIDDAC) through the base funding from the following research units: UIDB/00690/2020 (CIMO) and UIDB/04077/2020 (MEtRICs). The authors are also grateful for the funding of FCT through the projects NORTE-01-0145-FEDER-029394, NORTE-01-0145-FEDER-030171, funded by COMPETE2020, NORTE2020, PORTUGAL2020, and FEDER

Different Modelling Purposes

How one builds, checks, validates and interprets a model depends on its ‘purpose’. This is true even if the same model code is used for different purposes. This means that a model built for one purpose but then used for another needs to be re-justified for the new purpose and this will probably mean it also has to be re-checked, re-validated and maybe even re-built in a different way. Here we review some of the different purposes for a simulation model of complex social phenomena, focusing on seven in particular: prediction, explanation, description, theoretical exploration, illustration, analogy, and social interaction. The paper looks at some of the implications in terms of the ways in which the intended purpose might fail. This analysis motivates some of the ways in which these ‘dangers’ might be avoided or mitigated. It also looks at the ways that a confusion of modelling purposes can fatally weaken modelling projects, whilst giving a false sense of their quality. These distinctions clarify some previous debates as to the best modelling strategy (e.g. KISS and KIDS). The paper ends with a plea for modellers to be clear concerning which purpose they are justifying their model against

Manufacture of bone fracture plates based on glass fiber reinforced polyurethane composite: a gravity casting adapted process

The development of materials and devices to replace or restore damaged tissue functions has a prominent position in the scientific community, promoting the interest for metal-free alternatives, like composites. These proved to be a promising option as, besides new matrix and reinforcement combinations, new manufacturing methods tend to fulfil tailored requirements of the medical field. In this sense, we manufactured glass fiber/polyurethane composite plates for Osteosynthesis. Models based on commercial LCP implants were 3D printed and used to generated molds through a new adapted resin casting process. Additional mechanical tests showed that reinforcement additions between 10 wt% and 25 wt% caused an increase in the bending structural stiffness by 126%-165% when compared to pure polymer implants. In addition, if the number of holes is increased, from 4 to 6, the maximum stress reduces by 40%. The manufacturing process was an effective alternative as it presented low cost, high customization and allowed the development of complex geometries, resin injection and degassing.Foundation for Science and Technology (FCT, Portugal) and FEDER under Programme PT2020 for financial support to CIMO [UIDB/00690/2020] and national funding by FCT, PI, through institutional scientific employment program-contracts. Sika, for the material donations.info:eu-repo/semantics/publishedVersio