A parameter for quantitative analysis of plasticity induced crack closure

Numerical models have been successfully developed to predict plasticity induced crack closure (PICC). However, despite the large research effort a full understanding of the links between physical parameters, residual plastic wake and PICC has not been achieved yet. The plastic extension of material behind crack tip, Δyp, obtained by the integration of vertical plastic deformation perpendicularly to crack flank, is proposed here to quantify the residual plastic field. The values of Δyp and PICC were obtained numerically in a M(T) specimen using the finite element method. An excellent correlation was found between PICC and Δyp which indicates that this parameter controls the phenomenon, and can be used to quantify the effect of physical parameters. An empirical model was developed to predict PICC assuming that the residual plastic field is a set of vertical plastic wedges, that the linear superposition principle applies and that the influence of a particular wedge exponentially decreases with distance to crack tip. The model was applied successfully to predict PICC for different residual plastic fields which provided an additional validation of Δyp as the parameter controlling PICC

Simulation of crack growth in residual stress fields of pre-fatigued T-welded joints repaired by tungsten inert gas: a 3D approach

In this article, a three-dimensional finite element model (FEM) is used to predict the crack growth at the weld toe of a pre-fatigued T-joint that was repaired with a remelting technique. The numerical models were developed using the MSC.Marc software. Fatigue life is estimated by integrating the Paris-Erdogan law. The stress intensity factors are obtained by the virtual crack closure technique (VCCT). The T-welded joints, made of S355 steel, are obtained by covered electrode process and pre-cracked by fatigue. These welded joints were repaired by TIG dressing. The stress field generated by this dressing technique was estimated using a FEM model, presented in authors’ previous works. For the crack growth was used the VCCT three-dimensional model recently presented by the authors to predict the effect of overloads. The pre-existence of an elliptical crack at the weld toe, with a depth of 0.5 mm was considered. It is also studied the growth of pre-existing cracks which have been poorly repaired. It was observed that the TIG dressing produce residual compression stress fields on the weld toe that causes a delay in crack growth. The obtained results are compared with experimental ones. The fatigue’s lives obtained by simulations with the numerical model presented in this paper allows to evaluate the application conditions of TIG remelting technique in the repair of pre-cracked welded joints.info:eu-repo/semantics/publishedVersio

Study of data variability acquired by multiple profilometers

The accuracy and reliability of road monitoring data constitute a major concern among road designers, contractors and road administrations. These data may have foremost implications on rehabilitation strategies and, therefore, on costs and service life. For this reason, this paper aims to provide the interested bodies referred with useful information in relation to the variability of data acquired by road profilometers that is usually required. Five road profilometers, which belong to consultancy companies and research institutions, were used. Macrotexture and unevenness was measured on three selected road trials. Five runs were performed by each profilometer in both lanes of the road trials. The mean and the standard deviation were used to study the variability of the results. In relation to the macrotexture no significant differences were registered. For the unevenness the ratio between standard deviation and average MRI is higher than 20% and about twice the one found for macrotexture

Propagação vegetativa de clones de umezeiro.

bitstream/item/30468/1/boletim-82.pd

Análise da variabilidade do IRI obtido por vários perfilómetros

A irregularidade longitudinal, caracterizada habitualmente pelo Índice Internacional de Irregularidade (IRI – International Roughness Index), é um dos parâmetros de estado dos pavimentos rodoviários cuja variabilidade pode ter consequências relevantes nas estratégias de reabilitação e, consequentemente, nos custos e na sua vida de serviço. Por esta razão, este artigo tem por principal objectivo proporcionar às entidades referidas informação útil no que respeita à variabilidade do IRI, calculado a partir de dados obtidos por vários perfilómetros. Assim, foram seleccionados cinco veículos do tipo”multifunções”, que pertencem quer a empresas de consultadoria quer a instituições de investigação, e três trechos de estrada com camadas de desgaste em betão betuminoso drenante, betão betuminosos rugoso e betão betuminoso “convencional”. Cada veículo percorreu cinco vezes cada trecho nos dois sentidos de tráfego. O espaçamento adoptado para o cálculo do IRI foi de 100 m. A média e o desvio padrão foram os parâmetros usados para estudar a variabilidade dos resultados. De uma forma geral verificou-se que o valor do desvio padrão do IRI é 20 a 30% do valor da média

Analysis of test methods for texture depth evaluation applied in Portugal

Texture is a surface characteristic which has a very wide influence on pavements functional quality. It is currently assessed by a number of test methods. Road Administrations face the problems of dealing with data acquired by different methods and, in addition to that, the repeatability and reproducibility of the results. This paper presents an analysis of test methods used for texture depth evaluation in Portugal: the volumetric patch method and two methods based on surface profiles. Hence, three roads with low (dense asphalt), medium (“open texture asphalt”) and high (porous asphalt) texture depths were selected, where five profilometers made five runs. Two subsections of 150 m length were also selected to carry out the volumetric patch test. The texture indicators analysed were: the mean texture depth, the mean profile depth and the sensor measured texture depth. The average and the standard deviation were the statistical parameters used for the analysis. The results obtained for each method are significantly different and a good correlation between the mean profile depth and the sensor measured texture depth was established

Indicações técnicas para produção de sementes de plantas recuperadoras de solo para a agricultura familiar.

bitstream/CPACT-2009-09/11809/1/documento_227.pd

Agrobiodiversidade como base para sistemas agrícolas sustentáveis para a agricultura familiar.

bitstream/item/78746/1/Documento-354.pd