Residual stresses analysis in plasma dressed welded joints

The presence of residual stresses in a structure influences his behaviour. Fatigue strength of welded joints is significantly influenced by the presence of residual stresses, of flaws and notch sharpness at the weld toe. Plasma dressing at the weld toe is frequently used to remove flaws and to lessen the notch sharpness at the weld toe. With this re-melt, the stress field in the weld toe is also profoundly modified. The Finite Element Method (FEM) proves to be effective to simulate the stress fields generated by welding. The simplified two-dimensional models (2D) are efficient in this estimation. This paper presents a 2D finite element model to predict the residual stresses generated by Plasma dressing at the weld toe of a T-joint. The welded T-joints are made in St 52-3 steel, are obtained by covered electrode process and improved with plasma dressing. The analysis was developed with the MSC.Marc finite element code. The estimated stress field is validated with experimental stress results obtained using X-ray diffractio

Retrofitting of Welded Structures by TIG and Plasma Dressing

Due to economic and environmental constrains, the currently trend is to use the welded structures beyond their design lives. The predominant cause of in service failure of these aged structures is the fatigue of the welded joints. The use of improvement techniques in welded joints, as a repair technique, has been suggested by several authors. TIG dressing is one of the most promising of these repair techniques. However, the effectiveness of TIG remelting is closely linked to the depth of the repaired crack. The use of strain gauges can be effective to detect the presence of fatigue cracks in their initial phase of propagation, however their effectiveness in inspection programs on jobsite needs to be proven. Some TIG variants associated to recent technological innovations of fusion arc welding, are appointed to improve the penetration and the sustainability of the remelting process. In this article are presented some results of the work developed by the authors in the last years, relevant to assess the efficiency of sustainable repair, by TIG and plasma dressing, of welded structures. Relevance is given to the repair, complete or defective, of deep cracks, as well as the possible advantage of using TIG variants.info:eu-repo/semantics/publishedVersio

Simulation of crack growth in T-welded joints: residual stress field effect

In this article, a three-dimensional finite element model is used to predict the growth of cracks at the weld toe of a T-joint. The model is developed using the MSC Marc software. Fatigue life is estimated by integrating the Paris-Erdogan law and the stress intensity factors are obtained by the virtual crack closure technique. The influence of residual stresses generated by plastic deformation at the weld toe on the crack propagation speed is analyzed. The existence of residual compression stress fields causes a delay in crack growth. The obtained results are compared with the integration solutions of the Paris-Erdogan law using the stress intensity factor computed through the Mk factor proposed by Bowness and Lee, included in BS 7910 standard.info:eu-repo/semantics/publishedVersio

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

Numerical simulation of adhesively-bonded T-stiffeners by cohesive zone models

30th International Conference on Flexible Automation and Intelligent Manufacturing (FAIM2021) -15-18 June 2021, Athens, GreeceNowadays, the adhesive bonding method has a strong presence in the most varied industries. The bonding of composite materials with structural adhesives became more relevant in the industry, such as the aeronautical industry, which takes advantage of stiffener structures in composite materials using adhesive bonds. In any area of industry, large-scale application of a particular bonding technique requires reliable tools for the design and prediction of failure. This work evaluates the performance of a structural adhesive (Araldite® 2015) on a T-stiffener with composite adherends composed of an epoxy matrix reinforced with carbon fibers. The aim of the work is to numerically study, by the Finite Element Method (FEM) and Cohesive Zone Models (CZM), the behavior of different T-stiffener configurations under peel loads. A parametric study was carried out, including elastic stress analysis and maximum load (Pm) prediction, considering four geometrical parameters: flat adherend thickness (tP), stiffener thickness (t0), overlap length (LO) and curved deltoid radius (R). A significant effect was found for all studied parameters, on both stress distributions and Pm, enabling to define the optimal joint parameters for the T-stiffeners.info:eu-repo/semantics/publishedVersio

Effect of machining parameters on the mechanical properties of high dosage short carbon- fiber reinforced composites

The machinability of polymer matrix composites with fibers strongly depends on the type of fiber and dosage in question, having a high influence on the selection of tools and cutting parameters. The cutting temperature depends of rotation speed and the feed cutting tools and is significantly influencing on the quality of the machined surfaces and tool life. This paper presents the results of a current study concerning the effect of the rotation-cutting speed on the cutting temperature, roughness and tensile strength of short carbon fiber reinforced epoxy composites, potentially used in automotive and aeronautic industries. Composite plates were manufactured by compression molding, using short carbon fibers with 0.5 mm and 6 mm length. The increasing of the rotation-cutting speed increases significantly the temperature generated in the tool and slightly increases surface roughness. Tensile strength and Young閴s modulus are little sensitive to drilling speed. However, above 3000 rpm it was observed significant loss of stiffness, associated with the developed temperature in the machining process

Caraterização mecânica do aço S 355 a temperatura elevada

No presente trabalho pretende-se efetuar a caracterização mecânica do aço S 355 AR, EN 10025-4, a alta temperatura. A avaliação rigorosa da variação da tensão de cedência, do módulo de Young, do módulo de encruamento, do calor específico e do coeficiente de dilatação térmica, com a temperatura é essêncial na simulação numérica da distorção e das tensões residuais induzidas por campos térmicos. Embora esta informação esteja disponível em alguns códigos estruturais, como o Eurocódigo 3 parte 1.2, ela não inclui o efeito da composição química e da microestrutura. O aço S 355 AR é um material bastante utilizado em estruturas soldadas, onde a avaliação de distorções e tensões residuais é um problema usual. A caracterização mecânica do aço S 355 AR, EN 10025-4, foi obtida através de ensaios de tração isotérmicos realizados a temperaturas até 600 °C, por Calorimetria Exploratória Diferencial (DSC) realizada até à temperatura de 950 °C e por Análise Termomecânica (TMA) conduzida até aos 1350 °C. Os resultados obtidos diferem significativamente dos valores apresentados na parte 1.2 do Eurocódigo 3, para um aço ferrítico genérico.ABSTRACT: The present work aims to assess the mechanical characterization of S 355 AR steel, EN 10025-4, at high temperatures. The precise evaluation of the variation of yield stress, Young module, hardening module, specific heat and coefficient of thermal expansion, with the temperature is a key problem in numerical simulation of the distortion and the residual stresses induced by thermal fields. Although this information are available in some of the structural codes, like Eurocode 3 part 1.2, it does not include the effect of chemical composition and microstructure. The S 355 AR steel is a material commonly used in welded structures, where the evaluation of distortion and residual stresses is an usual issue. The mechanical characterization of the S 355 AR steel, EN 10025-4, were obtained by tensile tests conducted at temperatures up to 600 °C, by Differential Scanning Calorimetry (DSC) at temperatures up to 950 °C and by Thermomechanical analysis (TMA) conducted up to 1350 °C. The obtained results differ significantly from the values presented in Eurocode 3 part 1.2 for a general steel.info:eu-repo/semantics/publishedVersio

Stress intensity factor solutions for CTS mixed mode specimen

The Compact Tension Shear (CTS) specimen is used to study fracture and fatigue under mixed mode I/II loading conditions. The K solution available in literature was developed for fracture studies and does not consider the effect of crack deflection. The aim of present work is to develop KI and KII empirical solutions for cracks with different crack lengths, loading angles and crack orientations. A total number of 1120 cracked geometries were studied numerically with the finite element method and analytical solutions were fitted to the numerical predictions. An average difference of 0.53 % was found between numerical predictions and the analytical solution proposed for KI. For KII the difference is higher, but the equivalent stress intensity factor showed a difference of only 1% because KII is lower than KI. Experimental work was developed to study fatigue crack growth in CTS specimens. The cracks always adopted a direction approximately normal to loading direction, i.e., tend to propagate under mode I

Role of a family 11 carbohydrate-binding module in the function of a recombinant cellulase used to supplement a barley based diet for broiler chickens

Cellulases and xylanases display a modular architecture that comprises a catalytic module linked to one or more non-catalytic carbohydrate-binding modules (CBMs). CBMs have been classified into 52 different families, based on primary structure similarity. These non-catalytic modules mediate a prolonged and intimate contact of the enzyme with the target substrate eliciting efficient hydrolysis of the target polysaccharides. 2. A study was undertaken to investigate the importance of a family 11 CBM, displaying high affinities for barley -glucans, in the function of recombinant derivatives of cellulase CtLic26A-Cel5E of Clostridium thermocellum used to supplement a barley-based diet for broiler chicken. 3. The results showed that birds fed on diets containing the recombinant CtLic26A-Cel5E modular derivatives or the commercial enzyme mixture RovabioTM Excel AP displayed improved performance when compared with birds fed on diets not supplemented with exogenous enzymes. 4. It is suggested that the enzyme dosage used in this study (30 U/kg of basal diet), was probably too high for the efficacy of the family 11 CBM to be noticed. It remains to be established if the targeting effect resulting from the incorporation of CBMs in plant cell wall hydrolases may be effective at lower exogenous enzyme dosages

Crop -glucanase activity limits the effectiveness of a recombinant cellulase used to supplement a barley-based feed for free-range broilers

1. The supplementation of diets rich in soluble polysaccharides with microbial cellulases and hemicellulases decreases digesta viscosity and promotes broiler performance. 2. In contrast, recent experiments suggest that polysaccharidases are ineffective for improving the nutritive value of pasture biomass used by free-range broilers. However, the feasibility of using cellulases and hemicellulases to improve the utilisation of cereal-based feeds by pastured poultry remains to be established. 3. A study was undertaken to investigate the capacity of a recombinant cellulase from Clostridium thermocellum to improve the nutritive value of a barley-based feed for free-range pastured broilers of the RedBro Cou Nu RedBro M genotype. 4. The results show that supplementation of a barley-based diet with a recombinant -glucanase had no effect on the performance of free-range broilers, foraging in legume-based diets from d 28 to 56. In addition, the results confirm that the lack of effect of the recombinant enzyme in improving the nutritive value of the barley-based feed does not result from enzyme proteolysis or inhibition in the gastrointestinal tract. 5. Significantly, -glucanase activity was identified in the crop of non-supplemented animals. The data suggest that endogenous cellulases originated both from the barley-based feed and from the crop microflora. 6. The results presented here suggest that in older birds of slow-growing genotypes associated with free-range production systems, previously unknown sources of -glucanases, such as the feed and microbial symbiotic microflora, can affect the effectiveness of exogenous enzymes added to the feed