Finite element analysis of localised rolling to reduce residual stress and distortion

Fusion welding processes cause residual stress due to the uneven heat distribution produced by the moving welding torch. These residual stresses are characterised by a large tensile component in the welding direction. Due to the self-equilibrated nature of the residual stress, compressive ones are present in the far field next to the weld seam, which can cause different kind of distortion such as bending or buckling. Welding residual stress can be responsible of premature failure of the components, such as stress crack corrosion, buckling, and reduction of fatigue life. Localised rolling is a stress engineering technique that can be used to reduce the residual stress and distortion caused by welding. It induces plastic strain in the rolling direction, counteracting the plastic strain produced during welding. In this thesis three techniques were investigated, pre-weld rolling, post-weld rolling, and in situ rolling. These techniques have been seldom studied in the past, particularly pre-weld rolling; consequently the mechanisms are poorly understood. Finite element models allow stress and strain development during both welding and rolling processes to be better understood, providing an improved understanding of the mechanisms involved and aiding process development. A literature survey was done to find the state of the art of the computational welding mechanics simulations, stress management, and the residual stress measurement techniques, as well as the knowledge gaps such as, the thermal losses through the backing-bar in the thermal simulation, the frictional interaction in the rolling process, and the material properties of the steel used in the models. In the literature not many models that investigate the management of welding residual stress were found. After this, the general considerations and assumptions for the welding thermal mechanical models presented in this thesis were discussed. The effect of different backing-bar conditions, as well as different material properties where investigated. Both influenced the residual stress profile to varying degrees. In particular, temperature dependent heat loss to the backing-bar was necessary to capture the improved heat loss near the weld. The distortion predicted by the model was investigated to determine whether it was due to bending or buckling phenomena. Lastly, the temperature distribution and residual stress predictions were validated against thermocouple and neutron diffraction measurements conducted by Coules et al. [1–3]. Pre-weld rolling was the first of the three rolling methods considered, in which rolling is applied to the plates before performing GMA butt-welds. The principle behind this technique consisted in inducing tensile residual stress in the weld region before welding; therefore, it is similar to mechanically tensioning the weld, which can significantly reduce the residual stress and distortion. However, there was no significant change in the tensile residual stresses. On the other hand, it was possible to achieve a small reduction in the distortion, when the plates were rolled on the opposite surface to the weld; rolling in this way induced distortion in the opposite direction to the distortion induced by welding, reducing the magnitude of the latter. These results were compared with experiments conducted by Coules et al. [1,4]. A subsequent investigation combined pre-weld rolling with post-weld heating. With this additional process the residual stress and distortion were significantly reduced, and flatter residual stress profile was achieved. The post-weld rolling and in situ rolling techniques were discussed afterwards. In the post-weld rolling models, rolling was applied after the weldment was cooled to room temperature. In in situ rolling the roller was applied on top of the weld bead at some distance behind the torch, while it was still hot. The principle behind these techniques consisted in applying positive plastic strain to the weld bead region by a roller, counteracting the negative plastic strains produced in the welding process. Two roller profiles were investigated, namely, grooved, and double flat rollers. The post-weld rolling on top of the weld bead models, which used the grooved roller, showed good agreement against experimental results, producing a large reduction of the residual stress and distortion. Some discrepancies were present when the weld toes were rolled with the dual flat roller. The former roller was more efficient for reducing residual stress and distortion. The influence of different friction coefficients (between the roller and weldment, and between the backing-bar and the weldment), were investigated. It showed significant dependency on the residual stress distribution when high rolling loads were used. The frictional interaction constrained the contact area inducing more compressive stress in the core of the weld bead; therefore it produced more tensile residual stress in the surface of the weldment. Additionally, the influence of rolling parameters on the through-thickness residual stress variation was investigated. Low loads only influence the residual stress near the surface, while high loads affected the material through the entire thickness. When the dual flat roller was used to roll next to the weld bead, significant compressive residual stress was induce in the weld bead; however, the residual stress reduction was very sensitive to the contact of the roller to the weld toes; therefore, when rolling a weld bead that varies in shape along the weld, the residual stress reduction is not uniform and varies along the length. On the other hand, the in situ rolling did not produced significant residual stress or distortion reduction in all the cases analysed. The rolling occurred when the material was still hot and the residual stress was subsequently formed as the material cooled to room temperature. Numerical modelling was a very useful tool for understanding the development of stress and plastic strain during the welding and rolling processes

Application of Near Infrared Reflectance Spectroscopy (NIRS) for Macronutrients Analysis in Alfalfa (\u3ci\u3eMedicago sativa\u3c/i\u3e L.)

Near infrared reflectance spectroscopy was used to assess the mineral composition of alfalfa (Medicago sativa L.) as a tool for nutritional diagnosis. One hundred and ninety four (n = 194) samples of alfalfa from different locations representing a wide range of soils were used. Samples were reflectance scanned in a NIRS 6500 (NIRSystems, USA) instrument. The coefficients of determination (R2) of the regression estimate of the concentration of nitrogen, calcium, phosphorus, potassium, magnesium and sulphur and the errors in cross validation (SECV) were 0.93 (SECV: 1.6), 0.95 (SECV: 1.3), 0.93 (SECV: 1.9), 0.88 (SECV: 2.8), 0.82 (SECV: 1.9) and 0.75 (SECV: 4.7) respectively. The best NIRS predictions were obtained for calcium and nitrogen, meanwhile the poorest was obtained for sulphur

Chloroplast DNA Inheritance in the Orchid Anacamptis palustris Using Single-Seed Polymerase Chain Reaction

The modality of chloroplast inheritance in orchids has been investigated only in a few species due to the difficulties associated with the analysis of large progeny numbers from experimental crosses. To test chloroplast DNA inheritance in the orchid Anacamptis palustris, we took advantage of the presence of a highly variable minisatellite repeat located in the tRNALEU intron in the chloroplast genome. Seed progeny obtained from experimental crosses between parental individuals carrying different chloroplast DNA (cpDNA) minisatellite repeat numbers were analyzed using a single-seed polymerase chain reaction (PCR) protocol. All examined seeds displayed the maternal cpDNA haplotypes, indicating that cpDNA inheritance is strictly maternal in this Mediterranean orchid species. No evidence for paternal leakage was found. This finding concurs with results obtained from PCR amplifications of pollen massulae that exclude the presence of chloroplast DNA in the pollen tetrad

Application of Near Infrared Reflectance Spectroscopy (NIRS) to Forage Evaluation in Uruguay

Near infrared reflectance spectroscopy (NIRS) were used to assess the chemical composition of a wide range of forages. Nearly five hundred herbage samples covering a wide range of temperate pastures species and mixtures, previously analysed by conventional wet chemistry were scanned in reflectance with a NIRS 6500 (NIRSystems, Silver Spring, USA). The coefficients of determination in calibration (R2 ) and the errors in cross validation (SECV) were 0.98 (5.8), 0.94 (22.2), 0.97 (5.6), 0.94 (6.9) and 0.89 (19.7) for crude protein, in vitro organic matter digestibility, dry matter, ash and acid detergent fiber, in g kg –1 on a dry weight respectively. The high correlation between NIRS and chemical analysis found in this study showed the potential use of NIRS for prediction forage quality

Interpreting and Reporting Principal Component Analysis in Food Science Analysis and Beyond

Principal component analysis (PCA) is one of the most widely used data mining techniques in sciences and applied to a wide type of datasets (e.g. sensory, instrumental methods, chemical data). However, several questions and doubts on how to interpret and report the results are still asked every day from students and researchers. This brief communication is inspired in relation to those questions asked by colleagues and students. Please note that this article is a focus on the practical aspects, use and interpretation of the PCA to analyse multiple or varied data sets. In summary, the application of the PCA provides with two main elements, namely the scores and loadings. The scores provide with a location of the sample where the loadings indicate which variables are the most important to explain the trends in the grouping of samples

A performance prediction model for pumps as turbines (PATs)

In recent years, the interest towards the use of pumps operating as turbines (PATs) for the generation of electrical energy has increased, due to the low cost of implementation and maintenance. The main issue that inhibits a wider use of PATs is the lack of corresponding characteristic curves, because manufacturers usually provide only the pump-mode performance characteristics. In the PAT selection phase, the lack of turbine-mode characteristic curves forces users to expend expensive and time-consuming efforts in laboratory testing. In the technical literature, numerous methods are available for the prediction of PAT turbine-mode performance based on the pump-mode characteristics, but these models are usually calibrated making use of few devices. To overcome this limit, a performance database called Redawn is presented and the data collected are used to calibrate novel PAT performance models

Investigation of post-weld rolling methods to reduce residual stress and distortion

The mechanisms of post-weld rolling and how it reduces and eliminates residual stress and distortion are poorly understood. Finite element analysis was applied to two different methods of rolling: rolling the weld bead directly with a single roller and rolling beside the weld bead with a dual flat roller. The models showed that both rolling techniques were able to induce compressive stress into the weld region, which increased with rolling load. The distribution of stress was sensitive to the coefficients of friction between the workpiece and the roller and the backing bar. High friction coefficients concentrated the plastic deformation and compressive stress within the centre of the weld bead. Distortion can be eliminated by rolling; however, the experiments indicated that this was only achieved when applied to the weld bead directly

Hong-Ou-Mandel interference between independent III-V on silicon waveguide integrated lasers

The versatility of silicon photonic integrated circuits has led to a widespread usage of this platform for quantum information based applications, including Quantum Key Distribution (QKD). However, the integration of simple high repetition rate photon sources is yet to be achieved. The use of weak-coherent pulses (WCPs) could represent a viable solution. For example, Measurement Device Independent QKD (MDI-QKD) envisions the use of WCPs to distill a secret key immune to detector side channel attacks at large distances. Thus, the integration of III-V lasers on silicon waveguides is an interesting prospect for quantum photonics. Here, we report the experimental observation of Hong-Ou-Mandel interference with 46\pm 2% visibility between WCPs generated by two independent III-V on silicon waveguide integrated lasers. This quantum interference effect is at the heart of many applications, including MDI-QKD. Our work represents a substantial first step towards an implementation of MDI-QKD fully integrated in silicon, and could be beneficial for other applications such as standard QKD and novel quantum communication protocols.Comment: 5 pages, 3 figure

Mechanical behavior of biopolymer composite coatings on plastic films by depth-sensing indentation : a nanoscale study

Fundamental physical behaviors of materials at the nanoscale level are crucial when local aspects govern the macroscale performance of nanocomposites, e.g., interface and surface phenomena. Because of the increasing interest in biopolymer nanocomposite coatings for many different applications (e.g., optical devices, displays/screens, and packaging), this work investigates the potential of nanoindentation as a method for clarifying the interplay between distinct phases (i.e., organic and inorganic) at local level in thin biopolymer films loaded with nanoparticles. The nanomechanical features of pullulan nanocomposite coatings laid on polyethylene terephthalate (PET) were quantified in terms of elastic modulus (E), hardness (H), and creep (C) through an instrumented indentation test composed of a loading-holding-unloading cycle. Colloidal silica (CS) and cellulose nanocrystals (CNCs) were used as spherical and rod-like nanoparticles, respectively. An overall reinforcing effect was shown for all nanocomposite coatings over the pristine (unfilled) pullulan coating. A size effect was also disclosed for the CS-loaded surfaces, with the highest E value recorded for the largest particles (8.19\u202f\ub1\u202f0.35\u202fGPa) and the highest H value belonging to the smallest ones (395.41\u202f\ub1\u202f25.22\u202fMPa). Comparing CS and CNCs, the addition of spherical nanoparticles had a greater effect on the surface hardness than cellulose nanowhiskers (353.50\u202f\ub1\u202f83.52\u202fMPa and 321.36\u202f\ub1\u202f43.26\u202fMPa, respectively). As for the elastic modulus, the addition of CS did not provide any improvement over both the bare and CNC-loaded pullulan coatings, whereas the coating including CNCs exhibited higher E values (p\u202f<\u202f.05). Finally, CS-loaded pullulan coatings were the best performing in terms of C properties, with an average indentation depth of 16.5\u202f\ub1\u202f1.85\u202fnm under a load of 3c190\u202f\u3bcN. These results are discussed in terms of local distribution gradients, surface chemistry of nanoparticles, and how nanoparticle aggregation occurred in the dry nanocomposite coatings