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No / Convenient exact closed-form expressions are derived for calculating the bending stiffness of and stresses within loaded cylindrical bonded rubber blocks of circular cross-section. The particular solutions for simple bending, cantilever loading and apparent shear situations are deduced and studied in detail. The shapes of the deformed profiles are discussed and confirmation is provided that the previously adopted assumption of parabolic profiles of the deformed lateral curved surface is only valid for blocks of very small aspect ratio. In simple bending a relationship which is more realistic than those hitherto suggested is derived for the couple required to maintain a specified rotation of the loaded end of the block. In apparent shear an exact expression for the ratio of the true to the apparent shear modulus is derived, and compared with the experimental data. An improved approximate relation is deduced.

The purpose of this study is to examine the propagation of waves of finite deformation in rubbers through experiments and analysis. First, attention is focused on the propagation of one-dimensional dispersive waves in strips of latex and nitrile rubber. Tensile wave propagation experiments were conducted at high strain-rates by holding one end fixed and displacing the other end at a constant velocity. A high-speed video camera was used to monitor the motion and to determine the evolution of strain and particle velocity in rubber strips. Analysis of the response through the theory of finite wave propagation indicated a need for an appropriate constitutive model for rubber; by quantitative matching between the experimental observations and analytical predictions, an appropriate instantaneous elastic response for the rubbers was obtained. This matching process suggested that a simple power-law constitutive model was capable of representing the high strain-rate response for both rubbers used. Next, the propagation of one-dimensional shock waves in strips of latex and nitrile rubber is examined. Shock waves have been generated under tensile impact in pre-stretched rubber strips; analysis of the response yields the tensile shock adiabat for rubbers. The propagation of shocks is analyzed by developing an analogy with the theory of detonation. Attention is then focused on the propagation of unloading waves of finite deformation in a rubber specimen analytically and experimentally. A rubber strip stretched to many times its initial length is released at one end and the resulting unloading is examined. Dispersive waves as well as shock waves are observed in these experiments. Quantitative discrepancies between the analytical model and experimental observations are again used to motivate a power-law model. Hysteresis in the response is attributed to strain-induced crystallization and melting phase transitions in natural latex rubber, and to nonequilibrium microstructural deformation in nitrile rubber. Finally, a Kolsky experiment is conducted and analyzed under the framework of dispersive loading and unloading waves utilized in the previous experiments. In this experiment, a phase boundary is introduced separating low and high strain phases of the rubber and is demonstrated to persist as a stationary boundary in latex rubber. / text

Gummistövlar är en väsentlig del av många människors liv och utgör idag en viktig del av företaget Polarn O. Pyrets produktsortiment. Gummistövlar tillverkas av flera olika material såsom naturgummi (NR), styren-butadien-gummi (SBR), termoplastiska elastomerer (TPE) samt termoplaster. Syftet med rapporten är att, genom en materialjämförelse, reda ut hur en gummistövels miljöpåverkan ser ut. Genom en litteraturstudie har en jämförelse av råvaruutvinning och tillverkningsprocess utförts samt en översikt kring hur de olika materialen omhändertages vid livets slut. En gummistövel med en lång livslängd har i regel en lägre miljöpåverkan än en stövel med en kort livslängd. I och med en avsaknad av livscykelanalyser (LCA) för specifikt gummistövlar har detta emellertid försvårat och påverkat utformningen av arbetet. Sammanfattningsvis visade studien att råvaruutvinning av både NR samt syntetiskt gummi såsom SBR, TPE och termoplaster är samtliga material som har en negativ påverkan på den biologiska mångfalden i flera anseenden. Vad det gäller tillverkning av TPE och termoplaster har dessa material en lägre energiförbrukning och färre resurssteg vilket i sin tur genererar en lägre miljöpåverkan. Det är dessutom möjligt att återvinna dessa typer av material till skillnad från vulkat gummi såsom NR och SBR. Återvinningsmöjligheten är emellertid begränsad i och med en bristfällig infrastruktur för återvinning inom kläd- samt skoindustrin i allmänhet. / Rubber boots are an essential part of many people’s lives and today form an important part of the company Polarn O. Pyret’s product range. Rubber boots are made of several different materials such as natural rubber (NR), styrene-butadiene rubber (SBR), thermoplastic elastomers (TPE) and thermoplastics. The purpose of the report is to, through a material comparison, find out what the environmental impact of a rubber boot looks like. Through a literature study, a comparison of raw material extraction and a manufacturing process was made as well as an overview of how the various materials are handled at the end of life. A rubber boot with a long service life usually has a lower environmental impact than a boot with a short service life. However, due to the lack of life cycle analysis(LCA) for specific rubber boots, this has made it difficult and affected the design of the work. In summary, the study showed that raw material extraction of both NR and synthetic rubber such as SBR, TPE and thermoplastics are all materials that have a negative impact on biodiversity in several respects. As regards the production of TPE and thermoplastics, these materials have a lower energy consumption and fewer resource steps, which in turn generate a lower environmental impact. It is also possible to recycle these types of materials unlike vulcanized rubber such as NRand SBR. However, the possibility of recycling is limited due to a poor infrastructure for recycling in the clothing and shoe industry in general.

Styrene-Butadiene Rubber (SBR) is a form of rubber compound that is widely used in the tire industry. This is due to some of their unique characteristics such as high strength, high elasticity and resilience, high abrasion resistance, ability to absorb and dissipate shocks and vibrations, low plastic deformation, high deformation at low levels of stresses, and high product life. One of the most important and often overlooked causes of SBR degradation and eventual tire failure is 'rubber aging.' It can be defined as an alteration in the mechanical, chemical, physical, or morphological properties of elastomers under the influence of various environmental factors during processing, storing and use. Some of these environmental factors are humidity, ozone, oxygen, temperature, radiation (UV rays), etc. This study focuses on the effects of two of these factors acting in tandem, oxygen and temperature. In the past, studies have been conducted to observe the effects of rubber aging on the mechanical and wear properties of rubber. Studies have also been conducted to study the reactions taking place in rubber during aging and changes in its chemical structure. These studies use different modelling techniques and experiments to quantify the effects of aging. In this study, a material aging model that can predict the hyperplastic response of styrene-butadiene rubber (SBR) was mathematically developed using an integrated testing and continuum damage model framework. Coupling between the mechanical changes of SBR to the change in the chemical properties, specifically crosslink density (CLD) was also investigated. SBR dogbone shaped samples were accelerated aged in an aging oven at various temperatures and aging periods. Subsequently, hyperelastic tests were conducted to obtain the high strain response taking the 'Mullin's effect' into consideration. These responses were calibrated to different hyperelastic material models and the Arruda-Boyce model was chosen, due to its stable behavior and optimal fit. An aging evolution function was developed based on the variation in the model coefficients. This damage model is able to predict the hyperelastic response of SBR as it ages. A user material subroutine (UMAT) was also implemented in Abaqus based on the obtained aging evolution function to predict the stress response of SBR for varied applications. Additionally, to couple the chemical variations with the hyperelastic response, the rubber structure and composition was probed using Fourier-transform infrared spectroscopy (FTIR). The degradation of additives and SBR polymer chains were analyzed microscopically to explain the impact on the macroscopic properties. This study helps to correlate the change in crosslink density to ameliorate mechanical properties, such as strain at break, modulus, and stiffness. The effects of aging on the viscoelastic properties of SBR were also studied. Dynamic Mechanical Analysis (DMA) was used to characterize the viscoelastic response. Master curves of storage and loss modulus were generated using the time-temperature superposition principle (TTSP). The friction coefficient was estimated from the storage and loss modulus using a simplified form of the Persson equation [1]. CLD was also estimated from DMA data. Wear experiments were conducted on the Dynamic Friction Tester (DFT) for various aging conditions. The estimated friction coefficient was compared to the one from the experiments. Archard's law was used to correlate the frictional energy to the volume loss during wear experiments. Correlation between the wear and the viscoelastic properties of SBR is also studied. Finally, the lifetime of SBR for various aging temperatures is predicted using various models. [1] M. Ciavarella, "A Simplified Version of Persson's Multiscale Theory for Rubber Friction Due to Viscoelastic Losses," J. Tribol., vol. 140, no. 1, 2018, doi: 10.1115/1.4036917. / Master of Science / Elastomers or rubbers are they are generally referred to are an indispensable part of human life. They are made up of long-chain polymer units linked to one other through crosslinks. This peculiar morphology of rubbers is what gives them their unique characteristics. There are as many as 40,000 known products that use some form of rubber as the primary raw material. Apart, from this, they are also widely used in aviation and aerospace, automobiles, dampers and absorbers, civil engineering, electronics, medical, toys, clothing, sports, footwear, and so on. This is due to some of their unique characteristics such as high strength, high elasticity and resilience, high abrasion resistance, ability to absorb and dissipate shocks and vibrations, low plastic deformation, high deformation at low levels of stresses, and high product life. Over the last couple of years, it has also played a pivotal role in personal protective equipment (PPE) and masks worn by billions of people and frontline workers all over the globe. The fact that rubber is included in the EU's list of critical raw materials highlights its global importance. However, over the past several years, the rubber supply has dwindled. COVID-19 also caused disruptions in the supply chain of rubber. As the effects of COVID-19 are fading, there has been a spike in the demand for rubber; the primary reason being automotive tires! Even though substantial research is being conducted to try and replace rubber as a raw material with synthetic alternatives such as polyurethane, the excellent blend of damping, friction and wear characteristics, heat dissipation provided by natural rubber cannot be replicated by any of these laboratory compounds. Hence, at this time, there is an increased need to conserve and improve the longevity of rubber compounds. Styrene-Butadiene Rubber (SBR) is a form of a rubber compound that is widely used in the tire industry. One of the most important and often overlooked causes of SBR degradation and eventual tire failure is 'rubber aging.' It can be defined as an alteration in the mechanical, chemical, physical, or morphological properties of elastomers under the influence of various environmental factors during processing, storing and use. Some of these environmental factors are humidity, ozone, oxygen, temperature, radiation (UV rays), etc. This study focuses on the effects of two of these factors acting in tandem, oxygen and temperature. In the past, studies have been conducted to observe the effects of rubber aging on the mechanical and wear properties of rubber. Studies have also been conducted to study the reactions taking place in rubber during aging and changes in its chemical structure. These studies use different modelling techniques and experiments to quantify the effects of aging. The present study aims to model changes in the hyperelastic (large stretching) behavior of SBR using a Continuum Damage Mechanics (CDM) approach. This mathematical model is translated into ABAQUS, a finite element analysis software to study the mechanical response of components with various geometries and loading conditions. Secondly, the effects of aging on the viscoelastic behavior of SBR is studied. This helps us to estimate the cross-link density (CLD) as well as the friction coefficient of SBR as it is aged. The impact of aging on the wear and friction properties of SBR is studied experimentally. Finally, using various mechanical and chemical models the lifetime of SBR is estimated for various aging temperatures. Thus, the end goal of the study is to drive the development of new rubber compounds that will help improve the service life of rubbers and also have a positive impact on the environment.

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Mitigation of health and heat-build-up issues related to black, granulated crumb rubber infill (GCRI) in synthetic turf fields (STF) while maintaining acceptable impact absorption properties was the central goal of this study. The first step was establishing a STF baseline performance of GCRI samples that originated from several sources while elucidating the synergistic parameters between infill and turf that promulgate acceptable impact performance. Based on the knowledge base built on the GCRI-STF standard, three polymeric waste streams selected for their benign chemical contents, non-black colors and competitive low costs were evaluated as alternate turf infill materials: post-consumer carpet broadloom (PCCB), post-consumer carpet tile (PCCT) and recycled polyethylene terephthalate (PET) drink bottles. For ground PCCB carcass (the base on the carpet construction remaining after the face fibers were removed), the heterogeneous composition of unconfined fine particles and remaining short fibers prevented sufficient material integration to allow sufficient impact energy absorption. The ground PET homogeneous particles alone lacked sufficient impact absorption capabilities, and their synergistic interactions with the turf blade yarns were not sufficient to meet specified levels of impact performance. Only the PCCT infill crumb possessed a heterogeneous structure that effectively filled the STF to yield sufficient impact cushioning comparable to standard GCRI. In conclusion, PCCT was shown to be a technically-viable candidate for GCRI infill replacement, warranting further development to bring it into closer cost competitiveness to GCRI and ensure long-term wear and weathering performance in synthetic turf.

published_or_final_version / Mechanical Engineering / Doctoral / Doctor of Philosophy

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