Este trabalho teve como objetivo observar o resultado da variação dos parâmetros do processo FHPP (Friction Hydro Pillar Processing), dando-se atenção aos efeitos destes na microestrutura e na qualidade do reparo. O estudo foi realizado através de investigações metalográficas nos reparos obtidos, bem como análises via perfis de microdureza Vickers. Foram utilizadas diferentes forças axiais, que levaram a obtenção de reparos isentos de defeitos no seu preenchimento. Observou-se que o utilizando forças axiais maiores contribuíram para obter microestrutura mais refinada e homogênea, com formação predominante de martensita, menor tempo de processamento, menor quantidade de constituinte Martensita-Austenita e uma Zona Termicamente Afetada (ZTA) de menor tamanho. / This study aimed to observe the result of the variation of the Friction Hydro Pillar Processing parameters, giving attention to the microestructural effects and quality of repair. The study was carried out by metallographic investigations in repairs obtained and Vickers microhardness profiles. Were used different axial forces, which led to obtain no defects in repairs. It was observed that using higher axial forces helped to get more refined and homogeneous microstructure with predominant formation of martensite, lower processing time, less amount of Martensite-Austenite constituent and lower Heat Afecfted Zone (HAZ) size.

No description available.

With increasing miniaturization in microelectronics the wirebonds used in IC packages are witnessing a thrust towards fine pitch wirebonding. To have a precise control over loop height of the wirebond for fine pitch wirebonding, it is imperative to do mechanical characterization of the wirebond. The present work studies the mechanical properties of gold wire and wirebond using nanoindentation. The wirebond specimen surface was planarized using mechanical polishing. The loop height of the gold wirebond is directly proportional to the length of the heat affected zone (HAZ) above the ball of gold wirebond. Metallographic preparation of gold wirebond cross section reveals the presence of undesirable coarse grain structure in HAZ due to recrystallization and grain growth in the gold wire adjacent to the ball. The recrystallization temperature of our gold wire was found using D.S.C. to be 340.66°C. The doping elements present in the gold wire used, were identified using TOF-SIMS. Nanoindentation of the gold wire was done at different maximum loads to observe the hardness variation with load. The nanoindentation of gold wirebond has confirmed a v-shaped hardness profile in the HAZ. The hardness minima for the particular gold wire used with a ball size ratio of 2.4 was observed at distance of 160-170 µm from the neck of the ball. The elastic modulus was found to vary randomly and to be independent of the microstructure in the wirebond. A yield stress profile based on empirical hardness-yield strength correlation has been predicted for the gold wirebond. / Singapore-MIT Alliance (SMA)

The main purpose of this thesis is to improve the fundamental knowledge of non-isothermal tempering of martensite phase and its effects on the reduction in hardness (softening) with respect the base metal occurring at the heat affected zone (HAZ) of resistance spot welded dual-phase (DP) steels. This thesis also aims at understanding the influence of HAZ-softening on the joint performance of various DP steel grades. The tempering of martensite occurring at the sub-critical HAZ (SC-HAZ) of resistance spot welded DP600, DP780 and DP980 steels has been systematically evaluated by microhardness testing through Vickers indentation and the degree of tempering has been correlated to the HAZ-softening. From the joint performance analysis of similar and dissimilar steel grade combinations assessed through standardized testing methods, three important issues have been targeted: a) the joint strength (maximum load to failure), b) the location of failure (failure mode), and c) the physical characteristic of the weld that determines certain type of failure (weld nugget size). In addition, a partial tensile test has been conducted in order to evaluate the initiation of failure in dissimilar steel grade combinations. It has been shown that HAZ-softening lowered the weld size at which transition from interfacial to pullout failure mode takes place along with increased load-bearing capacity and higher energy absorption. Thus, it is concluded from mechanical testing that HAZ-softening benefits the lap-shear tensile joint performance of resistance spot welded DP steels by facilitating pullout failures through failure initiation at the SC-HAZ (tempered region). Instrumented nanoindentation testing was employed to further investigate HAZ-softening along the SC-HAZ by evaluating individual phases of ferrite matrix and tempered martensite islands. Although the ferrite matrix presented a slight reduction in hardness at nanoscale, higher reduction in hardness (softening) resulted for tempered martensite; thus confirming that tempered martensite is the major contributor to softening at micro-scale. A comparison between nanohardness and microhardness testing made at different distances from the line of lower critical temperature of transformation (Ac1) allowed revealing the actual extension of the SC-HAZ. In this regard, good correlation was obtained between nanohardness results along the SC-HAZ and the microstructural changes analyzed by electron microscopy (i.e., the tempering of martensite occurring at various distances far from Ac1 was correlated to low temperature tempering of dual phase steels). An in-depth analysis of the tempering of martensite phase at high temperature in DP steel subjected non-isothermal conditions i.e., rapid heating, extremely short time at peak temperature and rapid cooling (resistance spot welding), has been carried out mainly through analytical transmission electron microscopy (TEM). In addition, an isothermal tempering condition (i.e., slow heating and long time at peak temperature) in DP steel has been evaluated for complementing the analysis. Both non-isothermal and isothermal conditions have been correlated to the softening behaviour. TEM analysis of the base metal in the DP steel indicated that the morphology of the martensite phase is dependent on its carbon content, and its tempering characteristics are similar to that of equal carbon containing martensitic steel. The isothermally tempered structure is characterized by coarsening and spheroidization of cementite (θ) and complete recovery of the martensite laths; whereas precipitation of fine quasi-spherical intralath θ-carbides, coarser plate-like interlath θ-carbides, decomposition of retained austenite into elongated θ-carbides, and partial recovery of the lath structure were observed after non-isothermal tempering of DP steel. This difference in tempering behaviour is attributed to synergistic effect of delay in cementite precipitation due to higher heating rate, and insufficient time for diffusion of carbon that delays the third stage of tempering process (cementite coarsening and recrystalization) during non-isothermal. The finer size and the plate-like morphology of the precipitated carbides along with the partial recovery of the lath structure observed after non-isothermal tempering strongly influenced the softening behaviour of DP steel. The chemical analysis of θ-carbides through extraction replicas for three different DP steels revealed that the chemistry of the carbides is inherited from the parent DP steel during non-isothermal tempering at high temperature confirming that non-isothermal tempering DP steel is predominantly controlled by carbon diffusion.

The main purpose of this thesis is to improve the fundamental knowledge of non-isothermal tempering of martensite phase and its effects on the reduction in hardness (softening) with respect the base metal occurring at the heat affected zone (HAZ) of resistance spot welded dual-phase (DP) steels. This thesis also aims at understanding the influence of HAZ-softening on the joint performance of various DP steel grades. The tempering of martensite occurring at the sub-critical HAZ (SC-HAZ) of resistance spot welded DP600, DP780 and DP980 steels has been systematically evaluated by microhardness testing through Vickers indentation and the degree of tempering has been correlated to the HAZ-softening. From the joint performance analysis of similar and dissimilar steel grade combinations assessed through standardized testing methods, three important issues have been targeted: a) the joint strength (maximum load to failure), b) the location of failure (failure mode), and c) the physical characteristic of the weld that determines certain type of failure (weld nugget size). In addition, a partial tensile test has been conducted in order to evaluate the initiation of failure in dissimilar steel grade combinations. It has been shown that HAZ-softening lowered the weld size at which transition from interfacial to pullout failure mode takes place along with increased load-bearing capacity and higher energy absorption. Thus, it is concluded from mechanical testing that HAZ-softening benefits the lap-shear tensile joint performance of resistance spot welded DP steels by facilitating pullout failures through failure initiation at the SC-HAZ (tempered region). Instrumented nanoindentation testing was employed to further investigate HAZ-softening along the SC-HAZ by evaluating individual phases of ferrite matrix and tempered martensite islands. Although the ferrite matrix presented a slight reduction in hardness at nanoscale, higher reduction in hardness (softening) resulted for tempered martensite; thus confirming that tempered martensite is the major contributor to softening at micro-scale. A comparison between nanohardness and microhardness testing made at different distances from the line of lower critical temperature of transformation (Ac1) allowed revealing the actual extension of the SC-HAZ. In this regard, good correlation was obtained between nanohardness results along the SC-HAZ and the microstructural changes analyzed by electron microscopy (i.e., the tempering of martensite occurring at various distances far from Ac1 was correlated to low temperature tempering of dual phase steels). An in-depth analysis of the tempering of martensite phase at high temperature in DP steel subjected non-isothermal conditions i.e., rapid heating, extremely short time at peak temperature and rapid cooling (resistance spot welding), has been carried out mainly through analytical transmission electron microscopy (TEM). In addition, an isothermal tempering condition (i.e., slow heating and long time at peak temperature) in DP steel has been evaluated for complementing the analysis. Both non-isothermal and isothermal conditions have been correlated to the softening behaviour. TEM analysis of the base metal in the DP steel indicated that the morphology of the martensite phase is dependent on its carbon content, and its tempering characteristics are similar to that of equal carbon containing martensitic steel. The isothermally tempered structure is characterized by coarsening and spheroidization of cementite (θ) and complete recovery of the martensite laths; whereas precipitation of fine quasi-spherical intralath θ-carbides, coarser plate-like interlath θ-carbides, decomposition of retained austenite into elongated θ-carbides, and partial recovery of the lath structure were observed after non-isothermal tempering of DP steel. This difference in tempering behaviour is attributed to synergistic effect of delay in cementite precipitation due to higher heating rate, and insufficient time for diffusion of carbon that delays the third stage of tempering process (cementite coarsening and recrystalization) during non-isothermal. The finer size and the plate-like morphology of the precipitated carbides along with the partial recovery of the lath structure observed after non-isothermal tempering strongly influenced the softening behaviour of DP steel. The chemical analysis of θ-carbides through extraction replicas for three different DP steels revealed that the chemistry of the carbides is inherited from the parent DP steel during non-isothermal tempering at high temperature confirming that non-isothermal tempering DP steel is predominantly controlled by carbon diffusion.

No description available.

Objetivo: Evaluar la dimensión y morfología del cóndilo mandibular con el patrón esquelético Clase I utilizando tomografías Cone Beam en pacientes de 18 a más años durante el periodo 2016-2017. Materiales y métodos: Se evaluaron 71 tomografías procedentes de un centro de diagnóstico por imágenes en la ciudad de Lima- Perú. Se evaluó el diámetro antero -posterior (A - P) y el diámetro medio - lateral (M –L) en mm. También se evaluó la morfología del cóndilo en plano coronal y sagital. Resultados: Se obtuvieron las medidas del diámetro antero- posterior del cóndilo derecho con una media de 8.72 mm ± 1.25 y el izquierdo con una media de 8.50 mm ± 1.50. El diámetro medio – lateral del cóndilo derecho tiene una media de 19.24 mm ± 2.03 y el izquierdo 18.97 mm ± 1.87. La morfología del cóndilo con mayor prevalencia en el estudio fue redonda. La dimensión del cóndilo izquierdo en el plano medio – lateral tuvo mayor longitud en el sexo masculino (p>0.05). Conclusión: La morfología con mayor manifestación en este estudio fue de tipo redonda. Se demostró que existe diferencia significativa (p<0.05) del cóndilo izquierdo en el diámetro medio- lateral en relación al sexo. Sin embargo, no encontramos asociación entre la morfología del cóndilo y el sexo. / Objective: To evaluate the dimension and morphology of the mandibular condyle with the Class I skeletal pattern using Cone Beam tomography in patients aged 18 to over during the period 2016-2017. Materials and methods: We evaluated 71 tomographies from a diagnostic imaging center in the city of Lima, Peru. The antero-posterior diameter (A-P) and the medial-lateral diameter (M-L) in mm were evaluated. The coronal and sagittal plane morphology was also evaluated. Results: Measurements of the anterior-posterior diameter of the right condyle has a mean of 8.72 mm ± 1.25 and the left a mean of 8.50 mm ± 1.50. The medial - lateral diameter of the right condyle has a mean of 19.24 mm ± 2.03 and the left diameter has a mean of 18.97 mm ± 1.87. The condyle morphology with the highest prevalence in the study was round. The dimension of the left condyle in the mid - lateral plane had greater length in the male sex (p> 0.05). Conclusion: The morphology with the greatest manifestation in this study was of the round type. It was shown that there is a significant difference (p <0.05) of the left condyle in the medial-lateral diameter in relation to the sex. However, we found no association between the condyle morphology and sex.

El retratamiento de canales radiculares es una alternativa ante el fracaso endodóntico. Este procedimiento tiene como objetivo reducir los síntomas que pueden presentarse o agravarse posterior al tratamiento de endodoncia. El procedimiento del retratamiento de canales sigue la premisa que aparentemente la calidad del material de obturación en todo el sistema de canales es deficiente, por consiguiente, todo el material debe ser retirado. Actualmente, con mejores técnicas de análisis imagenológico es posible identificar el origen de la lesión apical, por lo tanto, es posible seleccionar los canales pulpares con tratamiento deficiente y poder ser tratados de forma individual. De esta manera, el retratamiento selectivo de canales podría evitar el desgaste innecesario de canales en buen estado. / Root canal Retreatment is an alternative in the face off endodontic failure. This procedure aims to reduce the symptoms that may occur or worsen after the endodontic treatment. The root canal retreatment procedure follows the premise that apparently the quality of the filling material in the entire canal system is deficient, therefore, all the material must be removed. Currently, with better techniques of image analysis it is possible to identify the origin of the apical lesion, therefore, it is possible to select the pulp canals with poor treatment and be able to treat them individually. In this way, the selective root canal retreatment could avoid the unnecessary wear of root canals in good condition. / Trabajo académico

No description available.

Objetivo: El propósito de este estudio fue determinar el grosor de la membrana de Schneider en tomografías de pacientes atendidos en el Centro Especializado en Formación Odontológica 2017-2019. Materiales y métodos: La población censal estuvo conformada por 163 TCCB. Los criterios de inclusión fueron: TCCB tomadas por un solo tipo de equipo radiográfico, TCCB de pacientes adultos parcialmente edéntulos en el sector posterosuperior, y TCCB que establezcan la salud de la membrana sinusal; y los criterios de exclusión fueron TCCB con defectos en la toma, TCCB de pacientes totalmente dentados o desdentados, TCCB que dificulten la determinación de la medida de la membrana de Schneider, TCCB que presenten un grosor de la membrana de Schneider (GMS) mayor a 3mm y TCCB de pacientes con patologías sinusales y/o maxilares; después de aplicar los criterios de selección se obtuvo una población de estudio de 90 TCCB. Resultados: El espesor promedio general obtuvo un valor de 1.3 ± 0.67 mm. El grosor promedio en pacientes masculinos fue 1.4 mm ± 0.67 mm y el femenino de 1.2 mm ± 0.70 mm. Según lado, en el derecho fue de 1.2 mm ± 0.72 mm y en el izquierdo de 1.2 ± 0.62 mm. Conclusiones: El espesor de la membrana de Schneider obtenido en el estudio fue de 1.3 mm. El sexo masculino obtuvo un valor mayor y según lado, los grosores fueron los mismos en la población estudiada.