Análise e medição da taxa de crescimento de trincas por fadiga em ferro fundido nodular

Dissertação (mestrado)—Universidade de Brasília, Faculdade UnB Gama, Programa de Pós-Graduação em Integridade de Materiais da Engenharia, 2018.O principal objetivo deste trabalho consiste na determinação da taxa de crescimento de trinca em um Ferro Fundido Nodular (FFN), conhecido comercialmente como GGG-40.3, onde foram testados vários corpos de prova compactos para tensão (CTS). O objetivo desta pesquisa consiste em determinar a vida em fadiga, propriedades de resistência do material e a variação do fator de intensidade de tensões () sob as condições de carga. Adicionalmente, se aplicou a técnica de Correlação Digital de Imagem (CDI) sobre a superfície do CTS. Por meio das imagens obtidas foi possível calcular os campos de deslocamentos e deformações nas amostras testadas. A CDI, além de acompanhar a propagação de trinca em tempo real, permite expandir a capacidade de análise do material.Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES).The main goal of this work is to determining the crack growth rate of a Nodular Cast Iron (NCI), commercially well known as GGG-40.3 Several Compact Tension Specimens (CTS) were tested. The aim of this research was to estimate the fatigue life, the material properties resistance and the variation of Stress Intensity Factor (K) of the material under load conditions. Additionally, a Digital Image Correlation (DIC) technique was simultaneously performed on the CTS surface. The displacement field was acquired during the fracture mechanics test and the strain field was calculate with the set of images. The DIC also allowed monitoring the fatigue crack propagation in real time. The traditional test procedure for determining the crack propagation in combination with the DIC technique allowed to expand the analysis capacity

Calcaneal tendon plasticity following gastrocnemius muscle injury in rat

Cross-talk between skeletal muscle and tendon is important for tissue homeostasis. Whereas the skeletal muscle response to tendon injury has been well-studied, to the best of our knowledge the tendon response to skeletal muscle injury has been neglected. Thus, we investigated calcaneal tendon extracellular matrix (ECM) remodeling after gastrocnemius muscle injury using a rat model. Wistar rats were randomly divided into four groups: control group (C; animals that were not exposed to muscle injury) and harvested at different time points post gastrocnemius muscle injury (3, 14, and 28 days) for gene expression, morphological, and biomechanical analyses. At 3 days post injury, we observed mRNA-level dysregulation of signaling pathways associated with collagen I accompanied with disrupted biomechanical properties. At 14 days post injury, we found reduced collagen content histologically accompanied by invasion of blood vessels into the tendon proper and an abundance of peritendinous sheath cells. Finally, at 28 days post injury, there were signs of recovery at the gene expression level including upregulation of transcription factors related to ECM synthesis, remodeling, and repair. At this time point, tendons also presented with increased peritendinous sheath cells, decreased adipose cells, higher Young’s modulus, and lower strain to failure compared to the uninjured controls and all post injury time points. In summary, we demonstrate that the calcaneal tendon undergoes extensive ECM remodeling in response to gastrocnemius muscle injury leading to altered functional properties in a rat model. Tendon plasticity in response to skeletal muscle injury merits further investigation to understand its physiological relevance and potential clinical implications