In recent years the interest for smaller, cheaper and more energy efficient vehicles hasincreased significantly. These vehicles are intended to be used in urban areas, where theactual need of large heavy cars is generally minor. The travelled distance is on average lessthan 56km during a day and most often there is only one person travelling in the vehicle. Manyof the established car manufacturers have recently started to take interest into this marketsegment, but the majority of these small vehicles are still manufactured by smaller companiesat a low cost and with little or no research done on vehicle traffic safety. This may be becausethere are still no legal requirements on crash testing of this type of vehicles.This report will examine road safety for Urban Light-weight Vehicle (ULV) to find criticalcrash scenarios from which future crash testing methods for urban vehicles can be derived.The term ULV is specific to this report and is the title for all engine powered three- and fourwheeledvehicles categorized by the European Commission. Other attributes than the wheelgeometry is engine power and the vehicles unladen mass. The maximum allowed weight for athree-wheeled ULV is 1 000kg and 400kg for a four-wheeled one.By studying current crash test methods used in Europe by Euro NCAP it has beenconcluded that these tests are a good way of assessing car safety. For light-weight urbanvehicles it has been concluded that some of these tests need to be changed and that some newtest scenarios should be added when assessing road safety. The main reasons for this is linkedto that vehicle’s with a weight difference of more than 150kg cannot be compared withcurrent test methods, and that crash tests are performed with crash objects with similar orequal mass in current safety assessment programs. This correlates poorly to the trafficsituation for light-weight urban vehicles since it would most likely collide with a far heaviervehicle than itself in an accident event.To verify the actual traffic situation in urban areas, accident statistics have beenexamined closely. The research has shown that there are large differences between rural andurban areas. For instance; 66% of all severe and fatal traffic accident occurs in rural areaseven though they are less populated. Even the distribution of accident categories has showndifferent in rural and urban areas. The United Nations Economic Commission for Europe(UNECE) has defined accident categories in their database which is widely used within theEuropean Union. By comparing each accident category’s occurrence, injury and fatality rate,the most critical urban accident categories were found in the following order. 1. Collision due to crossing or turning 2. Vehicle and pedestrian collision 3. Rear-end collision 4. Single-vehicle accident 5. Other collisions 6. Head-on collision Statistics also show that of all fatally injured crash victims in urban trafficapproximately; one third is travelling by car; one third by motorcycle, moped or pedal-cycle;and one third are pedestrians. This means that unprotected road travelers correspond to twothirds of all fatal urban traffic accidents, a fact that has to be taken into account in future crashtesting of urban vehicles. With all the information gathered a total of four new crash testscenarios for light-weight urban vehicles have been presented: • Vehicle-to-vehicle side impact at 40km/h with a 1 300kg striking vehicle to evaluate theoccupant protection level of the light-weight vehicle. • Vehicle-to-motorcycle side impact at 40km/h with motorcycle rider protection evaluation. • Pedestrian protection assessment at 40km/h over the whole vehicle front and roof area. • Rigid barrier impact at 40km/h corresponding to an urban single vehicle accident with aroad side object or a collision with a heavier or similar sized vehicle.

Any geometrical change and material transition renders a weak point accumulating stress concentrations in structural members. This research focuses on the transition between a sandwich panel and a single skin laminate, a setup commonly seen in yachts today. The need for different material layouts over a yacht’s complete structure leaves theses transitions inevitable. While the sandwich provides a strong and stiff, yet lightweight solution, the single skin is far more compliant and stronger when subjected to localised loads. The project included applying both finite element modelling and practical testing of the studied transition. Combining a computer based evaluation method with physical testing shortened production time and helped to focus the research on problematic areas of the design. Part of the project was also to highlight differences with these methods, their shortcomings and benefits, as well as how they can be used together as an effective way of research. The studied setups combined of three tapers including one to one, three to one, four and a half to one ratios and two different core thickness of the sandwich panel. Theses where partly modelled and tested in four point bending in a series of three load cases. Ranging from a shear load dominated to a much more mixed loading case including bending moment, the shear strength of the core could be seen as a reoccurring weak point of the structure. Results from modelling support earlier research on the benefits of a longer taper, lowering the stress concentrations at the tip of the transition, thus lowering the risk of further delamination. The practical testing indicated how the compression of the taper increased the shear strength of the core, making the taper far stronger than anticipated, leaving the uncompressed core material as the weakest point and the majority of times the source of failure. Successful in locating the critical element in the construction new difficulties with theconstruction could also be detected. The influence of the asymmetric laminate used, could be shown to affect the stress distributions but leaves more to be researched on how the laminates and core work together over the taper. The results and conclusions show that more work on this subject is needed, the complexity of the problem still needs tackled by decreasing the numbers of variables to reach a more general how tapers behave depending on the materials in use.

A Finite Element Analysis of a load test of the LAS-937 adapter has been made to check if there is any risk that the aluminuim in the upper interface of the adapter yields. The analysis was done in ABAQUS CAE. The reason for doing the analysis is that the adapter was measured to be oval after the load-test. Several different analysises were run to check how sensitive the model was to a higher load or lower yield strength in the alumium. It was found that the resulting stresses in the FE-model interface is not high enough to explain the ovality of the the interface. Even with the higher load or lower yield strength properties the deformations in the FE-model were not as high as the measured ovality.

AbstractCeramic materials have a wide range of applications in many fields, but their fragility limits theiruse in high strength and high stress environments. Therefore, by combining ceramic materialswith reinforcing agents, their mechanical properties can be improved. In this study, a reinforcingmaterial (PMMA) suitable for combining with ceramics was selected and compounded usingpolymer infiltration techniques. Models were first designed and modelled using computer-aideddesign software, then printed using an appropriate 3D printing process (stereolithography) andraw material ratios to ensure that the desired porous ceramic structure was obtained. Themechanical properties of the composites were assessed by conducting mechanical tests on theprepared samples. It was observed that the polymer composite samples exhibited higher strengthand toughness compared to pure porous ceramic materials. This is due to the presence ofreinforced PMMA, which fully fills the pores of the scaffold and forms a strong matrix, thusenhancing the stiffness of the scaffold. The differences in mechanical properties of samples withdifferent structures and different porosity were also compared in order to screen for the mostsuitable porous ceramic scaffolds. The results of this study show that the mechanical propertiesof ceramic composites can be significantly improved by manufacturing them through a 3D printingprocess. This material with improved mechanical strength has potential for a wide range ofapplications in areas such as aerospace, automotive engineering and medical devices. Futureresearch could further explore the combination of different reinforcing materials and differentporous structures to obtain even higher performance ceramic composites.

Composites are a useful type of material due to their ability to be created for specific applications. On the other hand composites often leads to a challenging optimization problem. Since composites often consists of more than two constituent materials it can be challenging to distribute the constituent materials in order to fulfill a certain mechanical property. The goal of this report is to construct an algorithm to optimize mechanical properties for a composite. The geometry of the composite is a 2-dimensional square with a pre-crack. The mechanical properties that the algoritm seeks to optimize is toughness and minimized stress in the crack tip. The results shows that the algoritm can be used in order to redistribute the constituent materials in order to improve a mechanical property.

Fiber/matrix interface cracking plays an important role in determining the final failure of unidirectional composites. In the present study, energy release rate (ERR) for fiber/matrix interface debond growth originated from fiber break in unidirectional composite is calculated using 5-cylinders axisymmetric and 3-D FEM models with hexagonal fiber arrangement. In the model the debonded fiber is central in the hexagonal unit which is surrounded by effective composite. The effect of neighboring fibers focusing on local fiber clustering on the ERR is analyzed by varying the distance between fibers in the unit. Two different scenarios are considered, one is the steady-state debond where debond are long and thus there is no interaction between debond tip and fiber break; the other case is when debond are relatively short when debond tip interacts with fiber break. The steady-state ERR is calculated from potential energy difference between a unit in the bonded region far away from the debond front and a unit in the debonded region far behind the debond front. The ERR for different modes of crack propagation is obtained from a FEM model containing a long debond by analyzing the stress at the debond front. For very short debonds, the ERR was calculated by both the J integral and the Virtual crack closure technique (VCCT).For steady-state debond growth, results show that in mechanical axial tensile loading fracture Mode II is dominating, it has strong angular dependence (effect of closest fibers) but the average ERR is not sensitive to the local fiber clustering. In thermal loading the Mode III is dominating and the average ERR is highly dependent on the distance to neighboring fibers. For short debod growth, results show that the debond growth is Mode II dominated and that the ERR strongly depends on the angular coordinate. The local fiber clustering has larger effect on the angular variation for shorter debonds and the effect increases with larger local fiber volume fraction. Finally, the ERR values from 5-cylinder axisymmetric model could be considered as upper bound for the 3-D hexagonal model.

The increasing industrial use of carbon fibre in e.g. aircraft and wind turbines calls for strategies for their recovery and possible reuse. In additional, tremendous amount of energy is needed to be able to manufacture pristine carbon fibres. The work that has been done was to manufacture engineering composite material made from recyclates. Processing scrap from PURE® was extensively studied in terms of its stability and process ability as a thermoplastic matrix material. In a second study polypropylene scrap material was reprocessed into a film by press forming and introduced into a stack of carbon fibre preforms made from recycled carbon fibres recovered via a pyrolysis process from aircraft structures. The preform stack was heated and the composite material was manufactured by press forming.A challenging issue in this work was to achieve the desired distribution of the recovered carbon fibres in the fibre preforms. It is well known that dispersion of reinforcement is of immense importance for quality and performance of the composite materials. Here, a paper making method is employed to distribute the recovered carbon fibres randomly in the plane. The quality of the manufactured novel, fully recycled, composite material regarding void content and consolidation was controlled by extensive microscopy. The resulting composite material was analysed in terms of its mechanical performance including elastic modulus, Poisson's ratio, strength and strain to failure as well as its creep resistance.

When a unidirectional (UD) fiber reinforced polymer composite is loaded in fiber direction in quasi-static or in a high stress cyclic tension-tension regime, many fiber breaks may occur in random positions already during the load increase in the first cycle. This is because fiber strain to failure in UD composites is lower than the polymer matrix strain to failure.In cyclic loading with constant amplitude we usually assume that fibers do not experience fatigue. Therefore the next step in damage evolution with increasing number of cycles may be development of interface cracks (debonds) growing along the fiber/matrix interface.Fracture mechanics concepts are applied and Mode II strain energy release rate GII related to debond crack growth along the fiber/matrix interface is used for damage evolution analysis.In Paper I analytical solution for Mode II energy release rate GII is found and parametric analysis performed in the self-similar debond crack propagation region. For short fiber/matrix debond cracks the self-similarity condition is not valid - due to interaction with fiber crack, GII is magnified. Thus in Paper II, numerical FEM simulations in combination with virtual crack closure technique are used in order to calculate GII for short debond cracks. The findings from GII analysis for self-similar and short debond cracks are summarized in simple expressions and then used in simulations of fiber/matrix interface debond crack growth in tension-tension fatigue using Paris law.In Paper III, debond growth in single fiber (SF) composites subjected to tension-tension fatigue is analyzed. Using the same procedure as for UD composites, first, an analytical solution for Mode II energy release rate GII is obtained for self-similar crack growth region. Then FEM calculations are performed in order to obtain GII magnification profiles for short debond cracks. For SF composites it was additionally found out that equal GII magnification profiles are obtained no matter if purely mechanical, purely thermal or combined mechanical and thermal load is applied to the composite. Thus for SF composites even simpler expressions can be used for simulations of debond growth using Paris law relation.

Reinforced polymer composites consist of continuous fibers embedded in a polymer matrix. The matrix is usually a thermoplastic or thermosetting resin. When thermosetting matrices are cured during the manufacture of composite parts, residual stresses develop within the part during the manufacture due primarily the thermally and chemically induced volumetric strains imposed on them. This can lead to shape distortions and sometimes weakening of the structure itself.Curing is the manufacturing process in which the thermoset resin is transformed from a liquid to a solid material. The molecular mechanisms involved in this process are quite complex and not well understood. In the macro-level, in addition to volumetric strains, heat is also generated since most thermoset polymerization reactions are exothermic. The mechanical properties of the thermoset also undergo dramatic changes. The material changes from its initial liquid state to a rubbery gel and finally to its vitrified glassy state.In modern day composite manufacturing, to accommodate for the shape distortions caused due to residual stress formation, the mold geometry is compensated. To do this, accurate predictions of the distortion behavior is required via computer simulations. This in turn requires simple mathematical models that can replicate the complex processes that take place during manufacture. One such process that requires attention is the curing of the thermoset. While models exist that assume elastic behavior during cure, they are not accurate throughout the entire cure process. Models based on viscoelastic material during cure offer better prospects in this perspective. However, currently models that are based on full viscoelasticity are either not well defined or are computationally tasking. Viscoelastic materials can be classified further in to thermorheologically simple and complex materials depending on their molecular weights. In layman’s terms, thermorheologically simple materials re those that obey the principles of time-temperature superposition (TTS). TTS requires that all response times (i.e., all relaxation or retardation time), depend equally on temperature. This is expressed by the temperature shift function. Master curves can be then generated extending the time scale beyond the range that could normally be covered in a single experiment. However to fully understand the development of viscoelasticity during cure it is also necessary that the effects of the degree of cure of the thermoset on these times be included in the model definition. This requires defining a cure shift function along with the temperature shift function. In the presented work, an attempt is made to develop a simplified methodology to characterize the viscoelastic material properties during curing. In the first paper, two different methods are investigated in a DMTA instrument to determine the effects of curing on the glassy state of the resin system LY5052/HY5052. A cure shift function was identified in the process. Based on observations it was concluded that the total shift function could be possibly defined as a product of the temperature and cure shift functions. Unique super-master curves were generated as a result. However, these curves showed a dependency of the rubbery modulus on the degree of cure. Hence, in the second paper, the effect of the degree of cure on the rubbery modulus was investigated. Following this a model was reformulated from an existing one and this was used to further simplify the super-master curves.

The polymer composites designed for high-performance applications are mostly based on carbon fiber reinforcement. The two most common precursors used currently for carbon fiber production are poly(acrylonitrile) and pitch (petroleum- or coal- based). As of today, the most promising alternative to these fossil originated raw materials is lignin. Previous research has mainly focused on carbon fiber production from pre-treated hardwood lignin with the addition of different softening agents. Softwood lignin has been considered difficult to melt, and thus, impossible to process by conventional melt spinning processes.The aim of the presented work is to find the way for melt spinning of softwood kraft lignin, by using lignin-derived additives. A method for isolation of kraft lignin was recently developed, making large amounts of high purity lignin available. The thermal properties of this type of lignin make it an interesting candidate for carbon fiber production. During this study, both unfractionated hardwood and softwood kraft lignin were used with addition of their fractionated counterparts, acting as softening agents. The spinning process of the lignin blends was optimized by adapting the processing temperature to the thermal properties of blends of different compositions. Different batches of lignin fibers were produced and characterized with scanning electron microscopy to evaluate the fiber diameter, the surface smoothness, the presence of pores and the shape of fiber cross-section.The fiber batch containing softwood kraft lignin and 10% fractionated hardwood kraft lignin was relatively easy to melt spin, despite the small amount of added fractionated hardwood lignin. Therefore, this batch was further processed into carbon fibers by oxidative stabilisation followed by carbonization in nitrogen atmosphere. X-Ray/Energy Dispersive Spectroscopy confirmed that carbon fibers containing above 90% carbon had been obtained. Mechanical characterization of produced lignin based carbon fibers was carried out. Single fiber tensile tests were performed to evaluate the stiffness and the strength of carbon fibers. In order to determine the properties of the lignin-based CFs, and to estimate the impact of the manufacturing parameters (such as die sizes and winding speeds), fibers of different diameters (≈30, 60 and 90 microns) were made and tested.Carbon fibers are brittle materials and therefore the experimental results (fiber strength) were treated by use of Weibull statistical distribution. Three fiber lengths (10, 20 and 40 mm) for each diameter were tested and strength data was approximated by two-parameter Weibull equation in order to obtain parameters of the strength distribution. The experimental results and predictions based on Weibull statistics showed a good fit.Although strength of the produced fibers is still significantly lower than that of commercially available carbon fibers, this thesis reports the first mechanical characterization of softwood kraft lignin based CFs.The carbon fiber production process differs depending on the raw material used. Most of the studies on lignin have considered hardwood lignin as raw material. As a first step towards a process optimized for softwood kraft lignin based carbon fibers, the stabilization step in the carbon fiber process was developed further.