A hydraulic damper plays an important role in tuning the handling and comfort characteristicsof a vehicle. Tuning and selecting a damper based on subjective evaluation, by considering theopinions of various users, would be an inefficient method since the comfort requirements of usersvary a lot. Instead, mathematical models of damper and simulation of these models in variousoperating conditions are preferred to standardize the tuning procedure, quantify the comfortlevels and reduce cost of testing. This would require a model, which is good enough to capture thebehaviour of damper in various operating and extreme conditions.The Force-Velocity (FV) curve is one of the most widely used model of a damper. This curve isimplemented either as an equation or as a look-up table. It is a plot between the maximum forceat each peak velocity point. There are certain dynamic phenomena like hysteresis and dependencyon the displacement of damper, which cannot be captured with a FV curve model, but are requiredfor better understanding of the vehicle behaviour.This thesis was conducted in cooperation with Volvo Cars with an aim to improve the existingdamper model which is a Force-Velocity curve. This work focuses on developing a damper model,which is complex enough to capture the phenomena discussed above and simple enough to beimplemented in real time simulations. Also, the thesis aims to establish a standard method toparameterise the damper model and generate the Force-Velocity curve from the tests performedon the damper test rig. A test matrix which includes the standard tests for parameterising andthe extreme test cases for the validation of the developed model will be developed. The final focusis to implement the damper model in a multi body simulation (MBS) software.The master thesis starts with an introduction, where the background for the project is described and then the thesis goals are set. It is followed by a literature review in which fewadvanced damper models are discussed in brief. Then, a step-by-step process of developing thedamper model is discussed along with few more possible options. Later, the construction of a testmatrix is discussed in detail followed by the parameter identification process. Next, the validationof the developed damper model is discussed using the test data from Volvo Hällered ProvingGround (HPG). After validation, implementation of the model in VI CarRealTime and Adams Caralong with the results are presented. Finally the thesis is concluded and the recommendations forfuture work are made on further improving the model. / En hydraulisk stötdämpare spelar en viktig roll för att fordonets hantering och komfort. Attjustera och välja en stötdämpare baserat på subjektiv utvärdering, genom att beakta olika användares åsikter, skulle vara en ineffektiv metod eftersom användarnas komfortkrav varierarmycket. Istället föredras matematiska modeller av stötdämpare och simulering av dessa modellerunder olika driftsförhållanden för att standardisera inställningsförfarandet, kvantifiera komfortnivåerna och minska testkostnaden. Detta skulle kräva en modell som är tillräckligt bra för attfånga upp stötdämparens beteende under olika drifts- och extrema förhållanden.Force-Velocity (FV) -kurvan är en av de mest använda stötdämparmodellerna. Denna kurvaimplementeras antingen som en ekvation eller som en uppslagstabell. Det är ett diagram somredovisar den maximala kraften vid varje maxhastighetspunkt. Det finns vissa dynamiskafenomen som hysteres och beroende av stötdämparens förskjutning, som inte kan fångas med enFV-kurvmodell, men som krävs för att bättre förstå fordonets beteende.Denna avhandling genomfördes i samarbete med Volvo Cars i syfte att förbättra den befintligastötdämparmodellen som är en Force-Velocity-kurva. Detta arbete fokuserar på att utveckla enstötdämparmodell, som är tillräckligt komplex för att fånga upp de fenomen som diskuteratsovan och tillräckligt enkel för att implementeras i realtidssimuleringar. Avhandlingen syftarockså till att upprätta en standardmetod för att parametrisera spjällmodellen och generera ForceVelocity-kurvan från de test som utförts på stötdämpartestriggen. En testmatris som innehållerstandardtest för parametrisering och extrema testfall för validering av den utvecklade modellenkommer att utvecklas. Det sista fokuset är att implementera stötdämparmodellen i en multi-bodysimulation (MBS) programvara.Examensarbetet inleds med en introduktion, där bakgrunden för projektet beskrivs ochdärefter definieras målen med arbetet. Det följs av en litteraturöversikt där några avanceradestötdämparmodeller diskuteras i korthet. Därefter diskuteras en steg-för-steg-process för attutveckla stötdämparmodeller tillsammans med några fler möjliga alternativ. Senare diskuteraskonstruktionen av en testmatris i detalj följt av parameteridentifieringsprocessen. Därefterdiskuteras valideringen av den utvecklade stötdämparmodellen med hjälp av testdata från VolvoHällered Proving Ground (HPG). Efter validering presenteras implementeringen av modellen iVI CarRealTime och Adams Car tillsammans med resultaten. Slutligen avslutas rapporten medslutsatser från arbetet och rekommendationer för framtida arbete görs för att ytterligare förbättramodellen.

Im Rahmen der Arbeit wurde ein semi-analytisches Berechnungsmodell für den Reibwert einzelner kugelförmiger Erhebungen erarbeitet, das die Berechnung der deformativen (μ_def) und adhäsiven (μ_adh) Reibanteile ermöglicht. Die Integration eines plastischen (Radius der Laufspur R_Spur) und eines viskosen (Rückstellwinkel ω) Verformungsanteils gestattet die Berechnung der realen Kontaktfläche während des Reibvorgangs. In Abhängigkeit des mittleren Kontaktdrucks kann damit der adhäsive Reibanteil μ_adh bestimmt werden. Die experimentelle Untersuchungen umfassten neben ungeschmierten Reibversuchen, die zur Ermittlung des gesamten Reibwertes (μ_ges) dienten, auch mit Silikonöl geschmierte Versuche aus denen sich μ_def ergibt. Anhand der Verifikationsversuche konnte einerseits gezeigt werden, dass beide Schmierungszustände zu gleichen Verformungen führen und andererseits wurde der Nachweis erbracht, dass der im Berechnungsmodell postulierte Zusammenhang zwischen dem Rückstellwinkel ω und μ_def Gültigkeit besitzt. Hierzu wurden Reibversuche mit segmentierten Kugeln durchgeführt, die eine gezielte Variation des Rückstellwinkels ω erlauben. Für beide untersuchten Reibpaarungen (Stahl | PE-UHMW und POM-C | PE-UHMW) kann abgeleitet werden, dass der deformative Reibanteil μ_def generell von untergeordneter Rolle ist (ca. 1/3 μ_ges) und der Einfluss des adhäsiven Reibanteils μ_adh überwiegt (ca. 2/3 μ_ges). Dabei sinkt μ_adh und folglich auch μ_ges mit zunehmendem Kontaktdruck p_(max,Ebene). Dieser wurde als verallgemeinerte Bezugsgröße eingeführt und beschreibt den maximalen Hertz´schen Kontaktdruck eines äquivalenten Kugel-Ebene-Kontaktes, der sich unter Eingabe des Kugelradius r_Kugel, der Normalkraft und der Verwendung der statischen E-Moduln beider Werkstoffe ergibt. Weiterhin zeigten die Untersuchungen, dass die oszillierende Bewegungsform im Vergleich zur rotierenden Bewegung immer einen erhöhten Reibwert μ_ges auszeichnet. Abschließend wurden noch Reibexperimente zu Mehrfachstrukturen aus POM-C mit je 6 Einzelerhebungen im Kontakt durchgeführt. Auch hier lag eine hohe Übereinstimmung zwischen Experiment und Modell vor. Es konnte gezeigt werden, dass Reibwerte für beide Bewegungsformen auf μ_ges ~ 0,13 gesenkt werden können. Bezogen auf den jeweiligen höchsten Reibwert (μ_(ges,rotierend) ~ 0,24, μ_(ges,oszillierend) ~ 0,34), welcher mit glatten Probekörpern ermittelt wurde, stellt dies eine erhebliche Reduktion dar. / In this thesis, a semi-analytical calculation model for the coefficient of friction (COF) of single spherical protrusions which allows the calculation of the deformative (μ_def) and adhesive (μ_adh) friction parts was developed. The integration of a plastic (radius of the running track R_Spur) and a viscous (rear angle ω) component of deformation allows the calculation of the real area of contact during the friction process. Depending on the mean contact pressure, the adhesive friction part μ_adh can be determined. The experimental studies included unlubricated friction tests, which served to determine the total COF (μ_ges), as well as tests being lubricated with silicone oil, from which μ_def is obtained. Based on the verification tests, it could be shown that both states of lubrication result in the same deformation and that the relationship between the rear angle ω and μ_def postulated in the calculation model is valid. Therefore, friction tests were carried out with segmented spheres, which allow a specific variation of the rear angle ω. For both friction pairings investigated (steel | PE-UHMW and POM-C | PE-UHMW), it can be concluded that the deformative friction part μ_def is generally of minor significance (approx. 1/3 μ_ges) and the influence of the adhesive friction part μ_adh predominates (approx. 2/3 μ_ges). Thereby μ_adh and consequently also μ_ges decreases with increasing contact pressure p_(max,Ebene). The latter was introduced as a generalised reference value and describes the maximum Hertzian contact pressure of an equivalent sphere-plane contact, which is obtained by entering the radius of the sphere r_Kugel, the normal force and using the static E-moduli of both materials. Furthermore, the investigations revealed that the oscillating form of motion always has an increased COF μ_ges compared to the rotating motion. Finally, friction experiments on multiple structures made of POM-C were carried out, each with 6 individual protrusions in contact. Also here, there was good agreement between the experiment and the model. It could be demonstrated that COF for both forms of motion can be reduced to μ_ges ~ 0.13. In comparison to the highest COF (μ_(ges,rotating) ~ 0.24, μ_(ges,oscillating) ~ 0.34), which were obtained with flat specimens, this is a significant reduction.

<p dir="ltr">Reinforced concrete elements are vulnerable to sliding against each other when shear forces are transmitted between them. Shear-friction is the mechanism by which shear is transferred between concrete surfaces. It develops by aggregate interlock between the concrete interfaces while reinforcement crossing the shear interface or normal force due to external loads contributes to the shear resistance. Current design provisions used in the United States (ACI 318-19, AASHTO LRFD (2020), and the PCI Design Handbook (2017)) include design expression for shear-friction capacity. However, the value of the reinforcement yield strength input into the expressions is limited to a maximum of 60 ksi. Furthermore, the concrete strength is not incorporated into the primary design expressions. These limits cause the potential contribution of high-strength reinforcement and high-strength concrete in shear-friction applications from being considered. Therefore, a research program was developed to investigate the possibility of improving current shear-friction design practice and addressing these current limits.</p><p dir="ltr">Specifically, an experimental program was conducted to evaluate the influence of high-strength reinforcement and high-strength concrete on shear-friction strength. In addition, a statistical analysis was performed using a comprehensive shear-frication database comprised of past tests available in the literature. The experimental program consisted of two phases. Phase I included 24 push-off specimens to study the influence of the yield strength of the interface reinforcement (Grade 60 and Grade 100) and the number and size of interface reinforcing bars (6-No.4 and 4-No. 5 bars) with three different interface conditions (rough, smooth, and shear-key). Phase II included 20 push-off specimens with rough interfaces to investigate the influence of the yield strength of the interface reinforcement (Grade 60 and Grade 100) and concrete strength (target strengths of 4000 psi and 8000 psi). The influence of these two variables was observed over a range of reinforcement ratios (ρ = 0.55%, 0.83%, 1.11%, and 1.38%).</p><p dir="ltr">The test results showed that the overall shear-friction strength was the greatest for rough interface specimens, followed by specimens detailed with shear keys. The smooth interface specimens had the lowest strengths. The results of both phases of the experimental program indicated that the use of high-strength reinforcement did not improve shear-friction capacity.</p><p dir="ltr">Furthermore, the results from the Phase II tests showed that increasing the concrete compressive strength led to increased shear-friction capacity. The test results from the experimental program were analyzed and compared with current design provisions, which demonstrated room for improvement of current design practice.</p><p dir="ltr">Following the experimental program, a comprehensive shear-friction database was analyzed, and multilinear regression was used to create a model to predict shear-friction strength. Factors were then applied to the model to provide acceptable design expressions for shear-friction strength (less than 5% unconservative estimates). The database was used to evaluate the factored model and current design provisions.</p><p dir="ltr">The research outcomes, especially the expressions for shear-friction strength that were developed and that include consideration of the concrete compression strength, along with the shear-friction tests demonstrating the lack of strength gain with the use of Grade 100 reinforcement, provide valuable information for the concrete community to help direct efforts toward improving current shear-friction design practice.</p>