The challenge tells us, that we should use the search field to access any sensitive information of the app by just entering an URL in the search field. Remembering one of the challenges above, we could try to access the data stored on the SD-card. Therefore, we have to enter the following URL:
In the first four articles, we have discussed solutions for the first eleven challenges in DIVA. In this last article of this series, we will discuss the remaining two challenges that are related to native code.
In this thesis, the possibility to numerically describing the behaviour that signifies shear type cracking in concrete is studied. Different means for describing cracking are evaluated where both methods proposed in design codes based on experiments and advanced finite element analyses with a non-linear material description are evaluated. It is shown that there is a large difference in the estimation of the crack width based on the calculation methods in design codes. The large difference occurs due to several of these methods do not account for shear friction in the crack face.
The finite element method is an important tool for analysing the non-linear behaviour caused by cracking. It is especially of importance when combined with experimental investigations for evaluating load bearing capacity or establishing the structural health. It is shown that non-linear continuum material models can successfully be used to accurately describe the shear type cracking in concrete. A method based on plasticity and damage theory was shown to provide accurate estimations of the behaviour. The methods based on fracture mechanics with or without inclusion of damage theory, overestimated the stiffness after crack initiation considerably. The rotated crack approach of these methods gave less accurate descriptions of the crack pattern and underestimated the crack widths. After verification of the material model, realistic finite element models based on plasticity and damage theory are developed to analyse the cause for cracking in two large concrete structures. The Storfinnforsen hydropower buttress dam is evaluated where the seasonal temperature variation in combination with the water pressure have resulted in cracking. With the numerical model the cause for cracking can be explained and the crack pattern found in-situ is accurately simulated. The model is verified against measurements of variation in crest displacement and crack width with close agreement. The construction process of a balanced cantilever bridge, Gröndal Bridge, is numerically simulated and a rational explanation of the cause for cracking is presented. It is shown that large stresses and micro-cracks develop in the webs during construction, especially after tensioning the continuing tendons in the bottom flange. Further loads from temperature variation cause cracking in the webs that is in close agreement with the cracking found in-situ. The effect of strengthening performed on this bridge is also evaluated where the vertical Dywidag tendons so far seem to have been successful in stopping further crack propagation.
In this paper, laboratory tests to failure of ten large deep beams with I-shaped cross-sections are presented. All beams had the same geometry with a shear span-to-depth ratio of 1.25 but differed in the amount of the vertical and horizontal web reinforcement. The presented results from the measurements consist of load-deformation curves, crack widths and crack patterns and strain distribution near the supports. The ultimate loads for these beams have been calculated with two strut-and-tie models and one truss model. The first strut-and-tie model calculates the tensile contribution of both reinforcement and concrete and takes into account their influence on the principal tensile stress. The second strut-and-tie model is a modification of the first one where the stress distribution along the strut is redefined. The third method is the truss model that is incorporated in a Design Code. The truss model gave the best result for the beams with a higher reinforcement ratio that exhibited in a shear compressive failure. The diagonal tensile failure that occurred in the beams with a small amount of web reinforcement was best captured with the modified strut-and-tie model.
In this paper, analyses based on laboratory tests of ten large deep beams with I-shaped cross-sections loaded to failure are presented. All beams had the same geometry with a shear span-to-depth ratio of 1.25, but differed in the amount of the vertical and horizontal web reinforcement. All beam tests resulted in shear failure, either diagonal tensile failure or shear compressive failure, depending on the amount of reinforcement. The diagonal tensile failure is generally considered to be the most difficult failure to treat numerically. In this study different material models incorporated in commercial numerical analysis tools are studied. Material models based on fracture mechanics with either rotated or fixed crack directions as well as a plasticity-based model are used in the analyses. The analyses show that the plasticity-based model in Abaqus gives good agreement with the experiments regarding crack pattern, load-displacement response and estimated crack widths. The models based on fracture mechanics in Atena and Response tend to give too stiff behaviour in the load-displacement response, but generally give a good estimation of the load capacity. The analyses performed with Atena gave good estimations of the crack pattern, and the models with a fixed crack direction also gave good estimates of the crack width.
As reinforced concrete structures reach the end of their design lives, technology for improving accuracy and efficiency of inspections and structural health monitoring rapidly progresses. Concrete cracking and reinforcement strains are two relevant parameters in assessing damage and safety ofthese structures. The use of Digital Image Correlation (DIC) systems and distributed Fibre Optic Sensors (FOS) to evaluate these parameters are two of the technologies that have been gaining momentum due to their advantages over other approaches. This study presents an experimental investigation of crack propagation of a reinforced concrete beam specimen through FOS and DIC.The FOS were positioned inside a groove carved in the rebar and in the concrete immediately outside the bar for comparison. The results showed a significant difference between both positions, with more reliable data coming from inside the bar. The addition of the DIC crack propagation images to the FOS analysis complemented the results, and good visual correlation was identified between both methods. This study is part of a broader research program, which aims at applying DIC and FOS for structural health monitoring of a real scale bridge structure.
The results show a slight increase in SCT for the highest, 460 gsm, and lowest, 245 gsm, grammages of the materials used in this study. The recyclable is affected minimally with only a few per cent, but it remains high. However, the material becomes a bit stiffer and suffers losses in tensile strength, elongation, and tensile energy absorption. The enhanced strength seen in SCT does not show for BCR. The crosslinked material tends to crack in the creases before and after bending, especially in the highest grammage. The Cobb results indicate crosslinking shows potential to be used as a barrier to make the material more water repellent.
Fracture toughness is one of the most important properties of a material. Being able toaccurately estimate the energy that goes into forming new crack surfaces is essential for the development of new materials, quality assurance, structural monitoring and failure analysis. Fracture toughness parameters are routinely determined by mechanical testing and are often used in numerical tools. Furthermore, fracture toughness is a common property in material specification. Numerical simulation of fracture toughness can reduce the need of mechanical testing and is sometimes the only viable alternative when mechanical testing is not an option, for example in component optimisation and in the assessment of operational structural components. However, complex fracture is a challenge in material modelling, which comes from that a material body is assumed to remain continuous in classical continuum mechanics. Classical continuum mechanics is formulated assuming a continuous body and that spatial derivatives are defined. However, this is not the case at cracks and other dis continuities. Complementing continuum mechanics with supplementary procedures for modelling discontinues can also add further challenges. Besides, the assumption of locality, that each material point only interacts with is immediate neighbouring points, becomes invalid for nanoscale geometries. Thus, fracture cannot easily be modelled. An alternative is therefore of interest. Peridynamics is a nonlocal extension of continuum mechanics with the constitutive model formulated as an integro-differential equation. The advantages of using an integral expression are foremost that long-range forces can be handled and that the theory is valid even in the presence of discontinuities, such as cracks, allowing unguided modelling of fracture. Since damage is introduced to the constitutive model of peridynamics, there is no requirement of supplementary procedures that can add further complications. Due to its nonlocal formulation, the method is also capable of capturing nano-effects. However, the use and reporting of fracture toughness parameters in peridynamics is a routine in its infancy as the method is under development.In this thesis, two fracture toughness methods, the classical J-integral and the essential work of fracture (EWF), are studied with peridynamics. Also, as the nonlocality of peri dynamics give rise to certain boundary effects, e.g. on crack faces, homogenisation is a part of the study. The thesis consists of two parts; an introductory summary with discussion and conclu sions, followed by a series of appended papers. The first paper concerns application of Rice's J-integral on displacement derivatives formulation in peridynamics with comparison to an exact analytical stress-strain-displacement specimen solution. The next two papers concerns homogenisation of a peridynamic bar, to remove the end effects, arisen from the nonlocality of peridynamics, to obtain an elastic behaviour exact to a classical continuum mechanics bar. The fourth paper is an implementation of the J-area integral into peridynamics, with study of various discretisation methods. Thereafter, in the last paper, Rice's J-integral and the nonlocal peridynamic J-integral are compared on various specimens, followed by an extension of the research to study EWF with peridynamics for the first time. The study includes a novel automated calibration at the interparticle bond level to simulate nonlinear elastic behaviour, which subsequently is complemented with softening and used for EWF modelling. As a part of introducing the peridynamic J-integral, the study also includes a proof of path independence. 2b1af7f3a8