Analysis of prior strain history effect on mechanical properties and residual stresses in beams

The crack compliance method (eeM) has attracted a lot of interest as an inexpensive method for the determination of residual stresses in materials compared to the use of Xray and neutron diffraction methods. The vast majority of the work found for the application of the eeM in the literature concentrated on the determination of residual stresses in annealed beam specimens. There is very little evidence of the verification of the method in cases where the material might have experienced prior strain loading effect such as Bauschinger effect before the residual stress is induced. This thesis has applied the eeM for the determination of residual stresses in bemus that were under Bauschinger effect before the residual stress was induced. The thesis also briefly considers the application of the eeM for the study of cyclic loading effect on the relaxation of residual stresses in beams. In order to achieve the aims highlighted above, the thesis develops a new efficient solution for the simultaneous determination of tensile and compressive stress-strain behaviour in materials under Bauschinger effect. The determination of these properties helps with the verification of the results of the eeM by using another relatively simple and inexpensive method based on the superposition of loading and unloading stresses. A new simple support method for beams subjected to electro-discharge machining (EDM) is also introduced. The new cutting arrangement allows free deformation of beams during cutting and allows the plane of cutting to be maintained without deviation. The experimental testing and verification procedure considers several factors such as different materials, heat treatment conditions, various levels of pre-straining and different fatigue load amplitudes. Several aspects of the crack compliance method are verified. The results obtained in all cases are generally very encouraging

Design and manufacture of a customised temporomandibular prosthesis

In this work, design, manufacture and surgical success of a personalised temporomandibular prosthesis is featured. A fused deposition modelling technique and Die forging process constitute the methodology used in a patient who had an amputation in the upper third branch of the mandible, without considering the joint capsule. The implant was designed using a processed resection image of a computational tomography and using the methodology of Özkaya and Nordin. The jaw operating conditions were simulated by the finite element method (FEM). The main considered factors were the morphological geometry of the patient, implant fixation in the first third of the branch, implant fixation on the chin, dental post for placement of the teeth, and the form of the sub-lingual fossa weight optimisation. Special consideration was to preserve the patients facial aesthetics.Peer Reviewe

Evaluation of the impact of residual stresses in crack initiation with the application of the Crack Compliance Method Part II, Experimental analysis

Abstract. The present work is based on a previous numerical simulation used for the introduction of a residual stress field in a modified compact tensile specimen. The main objective in that paper was to evaluate the effect that previous history has in crack initiation and to establish the new loading conditions needed to propagate a fracture. The experimental analysis presented in this paper was performed to compare and validate the numerical procedure. Several modified compact tensile specimens from a biocompatible material (AISI 316L) were manufactured to estimate the beneficial effect of a residual stress field. The specimens were separated in four batches; an initial group of uncracked specimens was used to establish an evaluation of the induction of a residual stress field produced by an overload; the remaining specimens were separated into three groups where a crack was introduced in each specimen (1 mm, 5 mm and 10 mm respectively) and the residual stress field caused by the application of an overload was determined. The assessment of all the residual stress fields introduced into the specimens was done by the application of the crack compliance method (CCM). The results obtained have provided useful information on the correlation between the numerical and experimental procedures. Furthermore, data concerning the understanding of diverse factors related to crack initiation are discussed in this paper. Finally, the beneficial aspects of the residual stresses are discussed

Evaluation of the impact of residual stresses in crack initiation with the application of the Crack Compliance Method Part I, Numerical analysis

Abstract. The understanding of how materials fail is still today a fundamental research problem for scientist and engineers. The main concern is the assessment of the necessary conditions to propagate a crack that will eventually lead to failure. Nevertheless, this kind of analysis tends to be more complicated, when a prior history in the material is taken into consideration and it will be extremely important to recognize all the factors involved in this process. In this work, a numerical simulation of the introduction of residual stresses, which change the crack initiation conditions, in a modified compact tensile specimen to change the condition of crack initiation is presented. Four numerical analyses were carried out; an initial evaluation was performed in a specimen without a crack and it was used for the estimation of a residual stress field produced by an overload; three more cases were simulated and a crack was introduced in each specimen (1 mm, 5 mm and 10 mm, respectively). The overload was then applied to set up a residual stress field into the component; furthermore, in each case the crack compliance method (CCM) was applied to measure the induced residual stress field. By performing this numerical simulation, the accuracy of the crack compliance method can be evaluated. On the other hand, elastic-plastic finite element analysis was utilized for the residual stress estimation. The numerical analysis was based on the mechanical properties of a biocompatible material (AISI 316L). The obtained results provided significant data about diverse factors, like; the manner in which a residual stress field could modify the crack initiation conditions, the convenient set up for induction of a beneficial residual stresses field, as well as useful information that can be applied for the experimental implementation of this research

Evaluación numérica del proceso de granallado y determinación del campo de esfuerzos residuales por medio del método de respuesta de grieta

In the open literatura around the world, it has been very well established the benefits that produces the shot peening process. Nevertheless, this process is a task, in some of the cases, of the development of handcrafted and/ or dependent on the experience of the workman. One of the principal virtues of this process, is the strengthening of the surface and increase in the yield stress of the material. This strengthening or increase of the resistance in the material, owes to the induction of a residual stress field of compressive type. The induction of this type of effect is extremely beneficial for the component, since this operation does that the elements submitted to cyclical loads raise its fatigue resistance (crack propagation)on the surface and could have hereby a longer useful life, and in the order hand, the applied loads to these elements could raise considerably. In this article, it is presented a comparison of the obtained residual stress field by shot peening by two methods, by the analytical and the finite element method (FEM), in order to obtain a confinable method for the evaluation of residual stresses, which approaches in major measurement to the registered ones by the experimental procedure. The numerical analysis performed in this work, it was done by 2D simulation, considering quasi-static conditions and not accounting random shot in the shot peening process. Also it is present the results obtained in the effect that the ball size produced. Hereby, in a later analyses, it will be possible to do an evaluation of the best results obtained by means of the FEM, changing certain factors that throw the suitable conditions of the parameters in the experimental tests, reducing cost and time

Conditions of stable reeling off a thread [Condiciones del proceso estable de desenrollado del hilo]

We consider the problem of a thread tension when a thread is reeled off from weft thread accumulator and balloons, passes through a thread conductor and moves farther with a constant speed. We apply the laws of conservation of momentum and conservation of energy to a finite part of a thread with the aim to estimate its tension and show that such consideration leads to different results if to assume a case without energy dissipation. As it follows from a number of experimental results in this case a thread often moves by jerks and vibrates although a speed of its end, by which it is pulled, and other conditions are maintained constant. To stabilize the nature of reeling off a thread it is advisable to increase of friction to dissipate an excess of kinetic energy acquired by a thread during the process

Engineering the optical and mechanical properties exhibited by a titanium dioxide thin film with gold nanoparticles

Thermo-optic and electrostrictive contributions to the nonlinear refractive index were observed in a titanium dioxide thin film with embedded gold nanoparticles. A sol–gel method was employed for preparing thin solid film samples. The nanosecond nonlinear optical properties and the Young’s modulus parameter were changed by shifting the optical absorption band associated with the localized surface plasmon of resonance of the gold nanoparticles with platinum. The third order nonlinear optical phenomena exhibited by the sample were induced by the second harmonic of a Nd-YAG laser with 532 nm wavelength; the nonlinear optical measurements were obtained by monitoring the transmittance and the amplitude modification for the vectorial components of the electric fields in a two-wave interaction. Optical evaluations were confirmed considering a straightforward measurement of the change in the refractive index of the sample when the sample was located in a Michelson interferometer

Numerical Analysis of a Dental Zirconium Restoration and the Stresses That Occur in Dental Tissues

When it is about restorative dental materials, aesthetics is traditionally preferred. This has led to the selection of materials very visually similar to the enamel, but unfortunately, their mechanical properties are not similar. This often translates into disadvantages than advantages. In the present work, a comparison is made of the stresses that occur during dental occlusion (dental bit) in a healthy dental organ and those that are generated in a dental organ with a dental zirconium restoration. Numerical simulation was carried out by means of the Finite Element Method, in computational biomodels, from Cone-Beam Tomography, to obtain the stresses generated during dental occlusion. It was found that the normal and von Mises stresses generated are substantially greater in the molar with restoration compared to those produced in the healthy molar. In addition, the normal function of the enamel and dentin to disperse these stresses to prevent them from reaching the pulp is altered. Therefore, it is necessary to analyze the indiscriminate use of this restoration material and consider other aspects, in addition to aesthetics and biocompatibility for the choice of restorative materials such as biomechanical compatibility

Design, Construction, and Operation of a High-Energy Mill for Handling Magnesium Powder

A high-energy mill was designed and built with the purpose of processing magnesium (Mg) powders. The main characteristics of the mill are grinding capacity of 1 kg and demolition elements of 10 kg; it has a distributed form to the interior ten blades of similar geometry, six of which are of the same size and four of them were increased in length in order to avoid the accumulation of the ground material. It has a jacket with a diameter of 240 mm as a cooling system to prevent high temperatures during grinding and possible chemical reactions; likewise, type 304 stainless steel was used for its construction. 10 mills were made during a period of 4, 6, and 8 hours, in order to obtain microparticles; with these particles, an analysis of X-ray spectroscopy was made to verify their physical and chemical characteristics. The outcome shows powder particles with dimensions of 0.1-4 mm, which will be used to the storage and handling hydrogen in the solid state (MgH2)