L’engouement pour le collage structural est important dans l’aéronautique. Actuellement, il n’existe pas de méthode de contrôle non destructive de l’adhésion dans un assemblage collé. Les méthodes de CND usuelles peuvent détecter au mieux des défauts majeurs de type décollement ou absence de colle. L’objectif de la thèse est donc de déterminer un indicateur ultrasonore en lien avec le niveau d’adhésion et la tenue structurale des assemblages collés.La première étape a consisté en l’élaboration d’éprouvettes étalons à adhésions variables de forme cisaillement simple. Trois traitements de surface différents ont été définis afin d’obtenir trois niveaux de force à rupture et donc trois niveaux d’adhésion distincts. Des cartographies détaillées du joint de colle sont obtenues par ultrasons. A l’issue des essais mécaniques les faciès de rupture sont analysés. Des contrôles supplémentaires par micro-tomographie X ont été réalisés. L’ensemble de ces essais ont permis de valider l’obtention d’éprouvettes homogènes et de niveaux d’adhésion maîtrisé. Un système expérimental spécifique a été réalisé pour développer des mesures d’acoustoélasticité qui permettent l’étude des variations locales de champ des contraintes. Pendant une sollicitation mécanique de type cisaillement simple, les variations de temps de vol dans l’aluminium en mode pulse-écho des éprouvettes sont analysées. Le dispositif est d’abord validé sur une éprouvette d’aluminium. Puis, il est démontré que sur une éprouvette de cisaillement simple, les bords d’un défaut, lieu de concentration de contraintes, sont visibles. Les simulations numériques réalisées donnent les mêmes tendances / The enthusiasm for structural bonding is important in aeronautic. Currently there is no method to test non-destructively the adhesion in a bonded assembly. The usual NDT methods can detect the most common defects like delamination or disbond. The aim of this thesis is to determine an ultrasonic indicator related to the level of adhesion and the structural strength of bonded assemblies.The first step was the development of calibrated samples. The specimens are single lap shear joints. Three different surface treatments have been developed to obtain three different levels of ultimate tensile strength and therefore three distinct levels of adhesion. Detailed cartographies of the adhesive joint are obtained by ultrasound. After mechanical testing the fracture surfaces are analyzed. Additional tests by microtomography were performed. They were used to validate the quality of samples. The objective of standards sample is achieved. A specific control system has been achieved to use acoustoelasticty to study the stress field in the bonded assembly. The variations of time of flight in the aluminum part in pulse-echo mode during mechanical test are analysed. First, the method is validated with an aluminum test piece. Then, it is shown, for a sample with defect, the edges of a defect are visible through the increase of stresses on its borders. Numerical simulations give the same trends.

Cartilage repair and/or replacement is necessary for many orthopaedic conditions including fissures from blunt trauma, autograft or allograft transplantation, and replacement of focal defects with biological or synthetic constructs. In cartilage repair, initial integration between the host tissue and repair site is desirable to allow for nutrient transport, molecular deposition to enhance fixation, and eventual stress transmission across the interface. It has been postulated that effective transport and crosslinking of newly synthesized collagen molecules across a repair site may be vital to the process of integrative repair, and recent experiments have correlated collagen deposition with the strength of such repair. Other investigations have shown that enzymatic degradation of the cartilage surface may enhance integrative repair and can increase bond strength of an adhesive to cartilage. This study explored a novel approach involving photochemical bonding of cartilage tissue samples through collagen crosslinking as a means to achieve rapid and effective initial fixation, with the goal of enhancing biological integration. Photosensitized collagen gels were first analyzed via FTIR to determine the crosslinking effects with respect to collagen type and photochemical mechanism. Using the photogellation FTIR results as a parametric guide, in vitro mechanical testing of photochemically bonded meniscal fibrocartilage and hyaline articular cartilage tissues was performed using a modified single-lap shear test. Finally, the cellular viability and bond stability of a photochemically bonded cartilage interface was evaluated over seven days of in vitro culture, where the bond strength was assessed by pushout of cores from annular defects. Results of this study have demonstrated the potential of combining enzymatic surface modification with photodynamic techniques to directly bond cartilage tissues for initial fixation.

Introduction: Cyanoacrylate gluing technique is the least strenuous treatment of varicose trunks which does not necessitate tumescent anaesthesia and post procedural stocking compression. In response to the long-term unavailability of commercial kits with N-butyl-2-cyanoacrylate (Histoacryl) in the Czech Republic, we used a modified technique, which is based on the technique of endovascular treatment of AV malformations in the brain and uses a mixture of cyanoacrylate and Lipiodol to clog. We evaluated the success of the method, complications and clinical improvement of chronic venous insufficiency. Parts of the work are histological findings of collected samples of veins at various time intervals. In an in vitro experiment, we compared the bond strength of a bonded shear to a tear device. The adhesive mix values used were compared with those of commercially available adhesives for this purpose. Patients and methods: Fifty-six limbs in 49 patients suffering from great saphenous vein or small saphenous vein insufficiency in combination with symptomatic chronic venous insufficiency and complicating comorbidities were treated with a modified endovascular cyanoacrylate glue application technique. A histopathological examination was conducted on vein samples from six. In each patient a sample of the...

Friction stir spot welding (FSSW) is quickly becoming a method of interest for welding of high strength steel (HSS) and ultra high strength steel (UHSS). FSSW has been shown to produce high quality welds in these materials, without the drawbacks associated with fusion welding. Tool grade for polycrystalline cubic boron nitride (PCBN) tools has a significant impact on wear resistance, weld quality, and tool failure in FSSW of DP 980 steel sheet. More specifically, for a nominal composition of 90% CBN, the grain size has a significant impact on the wear resistance of the tool. A-type tools performed the best, of the three grades that were tested in this work, because the grain size of this grade was the finest, measuring from 3-6 microns. The effect of fine grain size was less adhesion of DP 980 on the tool surface over time, less abrasive wear, and better lap shear fracture loads of the welds that were produced, compared to the other grades. This is explained by less exposure of the binder phase to wear by both adhesion and abrasion during welding of DP 980. A-type tools were the most consistent in both the number of welds per tool, and the number of welds that reached acceptable lap shear fracture loads. B-type tools, with a bimodal grain size distribution (grain size of 4 – 40 microns) did a little bit better than C-type tools (grain size of 12-15 microns) in terms of wear, but neither of them were able to achieve consistent acceptable lap shear fracture load values after the first 200 welds. In fact only one out of five C-type tools was able to produce acceptable lap shear fracture loads after the first 100 welds.

Fiber reinforced polymer (FRP) composites have been of interest to the structural engineering society since the earliest days of FRP composites industry. The use of such systems has been implemented in both new construction and for repair and rehabilitation of existing structures. Since the 1980s, researchers have developed a significant body of knowledge to use FRP composites in infrastructure applications; however, most of this established knowledge was concentrated on the use of traditional epoxy (EP) systems (epoxy matrix FRPs and epoxy adhesives). FRP composites with polyurethane (PU) matrices and adhesives have recently attracted the attention of a few researchers due to their potential advantages in constructibility and mechanical properties. The deployment of these systems is currently limited by a lack of knowledge on mechanical and durability performance. The objective of this research is to quantify the mechanical behavior of PU composites utilized in externally-bonded repair of common flexural and flexural-axial reinforced concrete systems. In addition, the mechanical performance, strength, and failure modes are compared directly with an epoxy-based composite by subjecting reinforced concrete specimens utilizing each of the matrix types (EP and PU) to the same protocols. The study presented therefore allows an objective comparison (advantages and disadvantages) between the two composite system used for repair and rehabilitation of concrete infrastructure. An experimental research program was designed with different length scales. Small-scale experiments were utilized to characterize the component level properties of the materials and bond to concrete, which include the flexural behavior as well as the pure shear behavior. The results of these small scale experiments were used to calibrate analytical models of the interface behavior between FRP laminate and concrete, and paved the way for the next level of the research which studied the behavior of each composite system at larger scales. The large scale experiments included flexural retrofitting of reinforced concrete girders and retrofitting of circular columns using FRP laminates. The large-scale experimental specimens were mechanically damaged prior to FRP repair and testing, making the testing more appropriate compared to common practice of repairing undamaged specimens.

Metallic utility poles, light poles, and mast arms are intermittently damaged by vehicle collision. In many cases the vehicular impact does not cause immediate failure of the structure, but induces localized damage that may result in failure under extreme service loadings or can promote degradation and corrosion within the damaged region. Replacement of these poles is costly and often involves prolonged lane closures, service interruption, and temporary loss of functionality. Therefore, an in situ repair of these structures is required. This thesis examines the failure modes of damaged metallic poles reinforced with externally-bonded fiber reinforced polymer (FRP) composites. Several FRP repair systems were selected for comparison, and a set of medium and full-scale tests were conducted to identify the critical failure modes. The material properties of each component of the repair were experimentally determined, and then combined into a numerical model capable of predicting global response. Four possible failure modes are discussed: yielding of the unreinforced substrate, tensile rupture of the FRP, compressive buckling of the FRP, and debonding of the FRP from the substrate. It was found that simple linear, bilinear, and trilinear stress-strain relationships accurately describe the response of the composite and substrate components, whereas a more complex bond-slip relationship is required to characterize debonding. These constitutive properties were then incorporated into MSC.Marc, a versatile nonlinear finite element program. The output of the FEM analysis showed good agreement with the results of the experimental bond-slip tests.

FRP laminates and fabrics, used as an externally bonded reinforcement (EBR) to strengthen or repair concrete members, have proven to be an economical retrofitting method. However, when used to strengthen long-span members or members with limited access, the labor and equipment demands may negate the benefits of using continuous EBR FRP. Recently, CFRP rod panels (CRPs) have been developed and deployed to overcome the aforementioned limitations. Each CRP is made of several small diameter CFRP rods placed at discrete spacing. To fulfill the strengthening length, CRP’s are spliced together and made continuous by means of overlaps (or finger joints). In this doctoral dissertation, the effectiveness of spliced CRPs as flexural strengthening reinforcement for RC members was investigated by experimental, analytical and numerical methods. The experimental research includes laboratory tests on (1) RC beams under four-point bending and (2) double-lap shear concrete specimens. The first set of tests examines the behavior of concrete members strengthened with spliced CRPs. Several beams were fabricated and tested, including: (a) unstrengthened, (b) strengthened with spliced CRPs, (c) strengthened with full-length CRPs, and (d) strengthened with full-length and spliced CFRP laminates. The double-lap shear tests serve to characterize the development length and bond strength of two commonly used CRPs. Several small-scale CRPs, with variable bond lengths, were tested to arrive to an accurate estimation of development length and bond strength. Several other specimens were additionally tested to preliminarily examine the effects of bond width and rod spacing. A 3D nonlinear finite element simulation was utilized to further study the response of CRP strengthened RC beams, by extracting essential data, that couldn’t be measured in the experimental tests. Additionally, analytical tools were added to investigate the behavior of tested bond and beam specimens. The first tool complements the double-lap shear tests, and provides mathematical terms for important characteristics of the CRP/concrete bond interface. The second tool investigates concrete cover separation failure, which was observed in the beam testing, for RC beams strengthened with full-length and spliced CRPs.

Fiber-metal laminates (FML) are the advanced materials that are developed to improve the high performance of lightweight structures that are rapidly becoming a superior substitute for metal structures. The reasons behind their emerging usage are the mechanical properties without a compromise in weight other than the traditional metals. The bond remains a concern. This thesis reviews the effect of pre-treatments, say heat, P2 etch and laser treatments on the substrate which modifies the surface composition/roughness to impact the bond strength. The constituents that make up the FMLs in our present study are the Aluminum 2024 alloy as the substrate and the carbon fiber prepregs are the fibers. These composite samples are manufactured in a compression molding process after each pre-treatment and are then subjected to different tests to investigate its properties in tension, compression, flexural and lap shear strength. The results indicate that heat treatment adversely affects properties of the metal and the joint while laser treatments provide the best bond and joint strength.

Fabric Reinforced Cementitious Matrix (FRCM) composites utilize a mineral mortar matrix as a substitute for epoxy resin that is used for Fibre Reinforced Polymer (FRP). This eliminates issues associated with the low thermal compatibility of FRP with concrete, susceptibility to UV radiation, and sensitivity to high temperatures in which organic polymers undergo vitrification. This study discussed the effect of varying parameters like the number of Carbon-FRCM (C-FRCM) layers (1, 2 and 3 layers), different anchorage configurations (non-anchored, spike anchor, wrap anchor and mechanical anchor), bond length (300 or 200 mm), and the fabric type (unidirectional and bidirectional) on the direct shear behaviour of C-FRCM composites bonded to a concrete substrate, especially the fibre-matrix bond which is the most common debonding interface of FRCM composites. Calibrated models of the bond – slip behaviour are provided based on the fabric type and number of fabric layers. The results indicate that the anchor type and the overall composite thickness are the main factors that control the failure mode of the composite. All properly anchored specimens using spike and wrap anchors failed due to fabric rupture. Moreover, a considerable number of the non-anchored specimens failed due to composite-substrate debonding, although premature fabric rupture was frequently observed. Furthermore, specimens with bidirectional fabric demonstrated shallower penetration of the strain into the composite which may be due to the horizontal fabric strands providing some anchorage for the longitudinal strands. They also exhibited slip initiation at a higher stress compared to unidirectional specimens. In addition, slip initiation stress of unidirectional specimens decreased with more fabric layers which may indicate that the additional layers have a lower bond efficiency. For the same reason, specimens with three layers of fabric generally experienced deeper strain penetration into the composite than one-layered or two-layered specimens regardless of the anchor type. The results also indicate that the use of bidirectional fabric and anchorage systems decreases the strain penetration into the composite and correspondingly, the effective length is shortened. Surface strain measurements captured using digital image correlation generally did not match the internal fabric strain values obtained from strain gauges.

The automotive industry is currently trying to replace the conventional steels to lightweight materials such as aluminum or carbon fiber to meet all stricter emission targets. When using such materials, traditional joining methods, such as spot welds, could be difficult to use. Therefore, more focus has been put on self-piercing rivets (SPR).In whole car models used in crash simulations, substitution models are used to model SPR joints. It is important to calibrate these models for different load cases. Volvo Cars Corporation (VCC) are currently calibrating using time-consuming physical tests where the SPR joint is subjected to loads in different directions. To save time, a way of virtually evaluating the SPR joint strength is therefore sought after. To do this, a method was developed using non-linear FEM in LS-DYNA. The method was then used to perform sensitivity studies concerning friction, sheet thickness and rivet geometry.The method developed can be divided into three parts. The process simulation, where the rivet insertion was simulated. A springback analysis, where the material is allowed to springback, closer resembling the real behaviour. Finally, the three destructive tests, lap-shear, cross-tension and KS2, were built using the geometry and initial values from the springback.For the process simulation, an explicit solution was used. To handle the large deformations present during the event, r-adaptivity was used together with a kill-element-method to describe failure, based on CrachFEM or Gissmo. The following springback analysis was then performed using one implicit step.For the destructive tests, a solid element representation of the SPR joint was created using the geometry and initial values from the springback. A shell-solid hybrid model was used to keep the computational time low.Using the method, a good correlation was found both for the process- and the destructive test simulations when compared to experiments. Furthermore, it could be concluded that friction, sheet thickness and rivet geometry affects the SPR joint strength and characteristics.