Compliant joints have significant advantages compared to rigid-body hinges due to a monolithic design and the absence of friction, which prevents effects like wear, backlash, and stick-slip behavior. However, the loading capability is often limited and the support stiffness generally decreases during rotation. A new design principle called closed form pressure balancing has been proposed as a solution to improve these limitations. By using an incompressible fluid as the main compliant element, the support stiffness becomes independent of rotation and buckling no longer limits the loading capability. This work analyzes the fundamental working principle behind closed form pressure balancing and introduces a 2D design model to determine stiffness properties. The design model is validated with a finite element model and used to construct an optimization strategy for optimum joint performance. Additionally, a conversion model and some practical considerations are presented for the transition to a 3D design model.@en

Full film lubricated bearings are machine components that excel in their ability to carry high loads with very little friction. Their main archetypes, passive hydrodynamic and active hydrostatic bearings, are used in a wide variety of applications, ranging from hydraulic pumps to high precision machine benches. They are most commonly lubricated using oil-based lubricants and have been a staple in improving machine performance for many decades. The continuous search for higher performing and more sustainable designs has given ample opportunity to revisit these machine components, and to investigate their possible implementation into machines and fields that so far have not been able to make use of their superior performance characteristics. This lack of increased implementation is often due to fundamental limitations of these components. Both the performance of hydrostatic and hydrodynamic bearings is directly coupled to their need for a thin lubricant film to provide stiffness and load capacity. For hydrostatic bearings in particular, this requirement can more accurately be defined as the need for the bearing surfaces to remain parallel to its counter-surface, separated by a thin film of lubricant in the order of 100 micrometer. Not only the performance, but also ecological constraints have been more dominant in recent years. The conventional use of oil-based lubricants has given researchers the motivation to look for cleaner and more sustainable lubricants. The engineering community keeps on moving forward to a higher performing and more sustainable future. This thesis investigates one fundamental design direction to obtain higher performance and increase the implementation field of full film bearings. By implementing compliant design, or the use of elastic elements, several facets of in particular hydrostatic bearing limitations are investigated. Two fundamental limitations are dominant throughout this dissertation: the design for changing counter surfaces and the design for multiple operating conditions. Several principles are introduced that improve the use of hydrostatic bearings for non-constant counter surfaces. These principles are the use of functionally graded materials to minimize the pre-loading effect the hydrostatic pressure has on the elastic bearing support, distributed whiffletree support-systems to increase bearing deformability, and the introduction of a compliant water-filled universal joint with superior stiffness characteristics compared to the state of the art. The universal joint makes use of the principle of closed-form pressure balancing, which is pressurizing an enclosed body of fluid to obtain low rotation stiffness while maintaining high support stiffness. All these principles are described through design models and are further investigated with the use of finite element models. The second dominant subject that is investigated in this dissertation is developing hydrostatic bearings that function for multiple operating conditions with the use of compliant elements. This principle, defined in this work as passive shape shifting, gives hydrostatic bearings more flexibility when it comes to designing for more discrete load cases, such as the one that can be found in hydraulic pumps. Besides describing this concept design principle with finite element models, a step towards real life application is also made in a scaled case study. By combining the previously mentioned compliant universal joint and a hydrostatic bearing using the principle of passive shape shifting, a contact-mechanics free alternative for axial piston pumps is proposed. This mechanism is designed for a scaled case study and validated through experimental work and finite element modelling. This thesis, which is conceptual in nature, combines these different design directions and therefor shows design directions that broaden the field of use for full film lubricated bearings by using elastic elements.@en

In tribotronic bearing design active components are used to adapt bearing performance to operating conditions. The principle of self-adaptive bearings has also been presented in literature in which a passive modification of geometry was used for a variation in conditions. This work presents an alternative design approach for self-adaptive bearings. This approach is focused on the shift between two known bearing geometries, where each of them is the preferred solution in a part of the operating regime. Using compliant elements in the bearing design allows for passive shape shifting. Four examples are presented which present this behavior for variable velocity and load conditions. The design approach could possibly provide a cheaper alternative for simple active bearing designs, or could be combined with active components in a tribotronics design to improve existing performance.

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Water lubricated bearings have been named in literature as a sustainable alternative to their oil-based counterparts. In order to clarify when water lubricated bearings are or are not a sustainable alternative, and inform design decisions, an analytical design tool is introduced based on anticipatory Life Cycle Assessment (LCA). This model is based on data from the bearing geometries, materials, and material combinations that have been the subject of research attention in the past 20 years in water lubricated bearing design. The model provides simple equations, fed with data from literature on materials, production and their tribological combination to provide initial insight on the sustainability of these types of bearings and future designs. A case study illustrates that quantifying environmental impacts can help determine when lubricant loss is more important than material choice, or vice-versa. The method aids bearing designers towards more sustainable designs.

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Hydrostatic bearings are superior in terms of their friction and load carrying characteristics when compared to contact based bearings, but non-usable in applications with non-constant curvature counter surfaces. A possible solution to this limitation is the introduction of deformable hydrostatic bearings components that cope with these required deformations. To reduce the required deformation of a single bearing pad, multiple pads can be connected through a so-called whiffletree support system. In this work, a symmetric whiffletree based hydrostatic bearing embodiment is introduced. A 2D quasi-static model is introduced that allows for determining the kinetostatic and path following properties of such a type of bearing. Design considerations are given regarding the joint rotational-, normal-, and shear stiffness of each individual joint, as well as basic bearing layout. The potential of a whiffletree suspended bearing is presented through the use of a case study.

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The SARS-CoV-2 pandemic resulted in shortages of production and test capacity of FFP2-respirators. Such facemasks are required to be worn by healthcare professionals when performing aerosol-generating procedures on COVID-19 patients. In response to the high demand and short supply, we designed three models of facemasks that are suitable for local production. As these facemasks should meet the requirements of an FFP2-certified facemask, the newly-designed facemasks were tested on the filtration efficiency of the filter material, inward leakage, and breathing resistance with custom-made experimental setups. In these tests, the facemasks were benchmarked against a commercial FFP2 facemask. The filtration efficiency of the facemask’s filter material was also tested with coronavirus-loaded aerosols under physiologically relevant conditions. This multidisciplinary effort resulted in the design and production of facemasks that meet the FFP2 requirements, and which can be produced at local production facilities.

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Introduction: The current COVID-19 pandemic has caused large shortages in personal protective equipment, leading to hospitals buying their supplies from alternative suppliers or even reusing single-use items. Equipment from these alternative sources first needs to be tested to ensure that they properly protect the clinicians that depend on them. This work demonstrates a test suite for protective face masks that can be realized rapidly and cost effectively, using mainly off-the-shelf as well as 3D printing components. Materials and Methods: The proposed test suite was designed and evaluated in order to assess its safety and proper functioning according to the criteria that are stated in the European standard norm EN149:2001+A1 7. These include a breathing resistance test, a CO₂ build-up test, and a penetration test. Measurements were performed for a variety of commercially available protective face masks for validation. Results: The results obtained with the rapidly deployable test suite agree with conventional test methods, demonstrating that this setup can be used to assess the filtering properties of protective masks when conventional equipment is not available. Discussion: The presented test suite can serve as a starting point for the rapid deployment of more testing facilities for respiratory protective equipment. This could greatly increase the testing capacity and ultimately improve the safety of healthcare workers battling the COVID-19 pandemic.

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Compliant mechanisms consist of a monolithic body and obtain motion through elastic deformation. Multiple compliant flexure designs are known but their translational to rotation stiffness ratio is often limited. This work introduces a novel compliant hinge design with increased stiffness ratio compared to the state of the art compliant hinges. The hinge functions by having an encapsulated fluid medium that contributes to high normal stiffness, but doesn’t influence the rotational stiffness. A 2D design model is presented that shows the effect of the geometry on the stiffness ratio performance. Subsequently, a computational 3D analysis is performed and the resulting design is realized as a demonstrator. The performance is compared to conventional compliant hinges based on the stiffness ratio. This shows an increase of at least a factor 30 on the stiffness ratio

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Compliant shell mechanisms utilize thin-walled structures to achieve motion and force generation. Shell mechanisms, because of their thin-walled nature and spatial geometry, are building blocks for spatial mechanism applications. In spatial compliant mechanism design, the ratio of compliance is the representation of the kinetostatics involved. Using shell mechanisms in concept design, however, can prove difficult without a uniform characterization method. In this article, we make use of compliance ellipsoids to achieve characterization of the ratio of compliance for shell mechanisms. Ten promising shells are presented with the kinetostatic characteristics, combined with a uniform method of determining the kinetostatic characteristics for other unknown shells. Finally, we show how shells are indeed a valid alternative in the spatial mechanism design, compared to conventional flexure mechanisms.

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Deformability of hydrostatic bearings could potentially increase their application range significantly. When a bearing is made compliant, the film pressure starts to influence the deformation of the support itself. This effect, called compliant-hydrostatic pre-loading, is especially crucial to take into account when designing highly deformable hydrostatic bearings. This work introduces the principle of pressure profile matching to minimize the effect of this pre-loading. A two-dimensional design model is introduced to determine the performance of such an elastic bearing utilizing stiffness profile matching. Additionally, an extension to the model is presented to analyze the basic performance of these type of bearings over small counter surface eccentricities. Finally, an embodiment of such a material distribution is presented utilizing functionally graded materials. These embodiments are analyzed with respect to their failure behavior, showing an improved shear stress and strain energy density distribution with the functionally graded supports when compared with conventional elastic supports.

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Traditionally hydrostatic slider bearings have rigid surfaces, and therefore require a well-defined and rigid counter surface with a constant or zero curvature. However, when the counter surface has a curvature varying along the path of the hydrostatic bearing, that hydrostatic bearing needs to follow that curvature. For this bearing compliance is required. This work introduces a new principle to increase the performance of compliant hydrostatic bearings by means of open form pressure balancing. A numerical example is provided to show the potential by comparing axi-symmetric parallel bearing performance of different geometries. Using thin-film assumption, the model is solved using an elasto-hydrostatic approach. The film height, pressure profile and load capacity are presented. This work provides the initial findings for pressure balanced parallel bearings.

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Spatial compliant mechanism are challenging to design owing to their complex spatial kinetic and kinematic behavior. There are many synthesis methods to design compliant mechanisms, but they are often presented for planar mechanisms or have other limitations such as lack of designer input possibilities. In this paper a method based on the compliance ellipsoid is presented to create compliant mechanism topologies for spatial design cases. The result of this synthesis method is a qualitative concept which fundamentally creates the desired kinetic and kinematic profile. This concept can then be further refined using a large deformation eigentwist analysis, presented here. Lastly, these tools are used in a design example to show its potential.

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The DOT concept for offshore wind energy is a seawater hydraulic network where turbines are directly coupled to a centralized hydro-power platform. The essential missing component is a low-speed hydraulic pump that uses seawater as its hydraulic medium. This low speed hydraulic pump is currently being designed and tested by DOT, where novel machine components have been developed. This paper describes the development of an interface between an oval running track which is used as eccentricity to actuate a hydraulic piston. Several approaches have been performed as well as prototyping and validation steps. These steps as well as the design approach are presented in this work.@en

In this paper a first iteration of a new scoliosis brace design and correction strategy is presented using compliant shell mechanisms to create both motion and correction. The motion profile of the human spine was found using a segmented motion capture approach. The brace was designed for a case study using a conceptual ellipsoid design approach. The force controlled correction profile was re-invented using a two fold zero and positive stiffness profile. These force generators were built and validated to prove their zero stiffness characteristic. The kinematic part of the brace was detail designed with the correct order of magnitude and validated through their force-deflection characteristic. The end result was a first iteration of a new brace validated and analysed on some critical components which can form the basis for a future biomechanical study.

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