Residual Peak Research Articles

Correlation of right ventricular outflow tract residual disease on post-op transesophageal echocardiography and discharge transthoracic echocardiography after tetralogy of fallot repair.

Post-operative transesophageal echocardiography (TEE) is standard of care to evaluate for residual disease and quality of surgical repair. The residual lesion score (RLS) as defined by the pediatric heart network explored the impact of residual lesions on outcomes using discharge transthoracic echocardiogram (TTE). In tetralogy of fallot with pulmonary stenosis (TOF/PS), the residual right ventricular outflow tract (RVOT) gradient is one marker of quality of repair. Given peri-operative differences in hemodynamics, this study aims to define the correlation between TEE and discharge TTE RVOT gradient. This single center retrospective study included patients with TOF/PS undergoing primary repair with accompanying perioperative TEE and discharge TTE. TEE and TTE measurements were compared. An RLS based on the type of repair was assigned to the post-operative TEE based on the RVOT doppler velocity. TEE RVOT peak velocity and VTI correlated with TTE RVOT peak velocity (Spearman rank correlation coefficient = 0.62 (p < 0.001)) and VTI (Spearman rank correlation coefficient = 0.66 (p < 0.001)) at time of discharge. Application of RLS at the time of the TEE does not accurately reflect RLS at the time of discharge based on current criteria (p-value based on McNemar's Chi-squared test = 0.24). The ability of post-op TEE measurement to predict need for re-intervention is just as effective as TTE. On ROC analysis, the TEE RVOT peak velocity had similar AUC (0.672) compared to discharge TTE RVOT peak velocity (0.721) on predicting need for re-intervention. After surgical repair of TOF/PS, there is a strong correlation between post-op TEE and discharge RVOT peak velocity. TEE offers a chance to guide immediate re-intervention if needed and may be applied to severe residual post-op RVOT peak velocity. Further studies are needed to identify RLS based on TEE and its relationship to outcomes and intraoperative management.

Impact of three-dimensional imaging and printing on septal myectomy results-single centre's experience.

To assess changes in the results of septal myectomy (SM) following introduction of three-dimensional (3D) imaging and 3D printing in surgical interventions planning and performing in the single-centre settings. Between January 2007 and March 2022, 268 consecutive symptomatic patients with hypertrophic obstructive cardiomyopathy and peak pressure gradient at obstruction area ≥50 mmHg underwent conventional SM (n = 112) or SM with heart 3D modelling (n = 156). For comparative analysis, we used propensity score matching (PSM) by 14 variables and there were formed group 1PSM (conventional SM, n = 77) and group 2PSM (3D-modelled SM, n = 77). It was noted for group 2PSM: larger mean resected myocardium mass [10.0 (standard deviation 4.3) vs 5.2 (standard deviation 2.7) g], P < 0.001, no mitral valve replacement cases [0 vs 28 (36.4%), P < 0.001], no iatrogenic ventricular septal defects cases [0 vs 6 (7.8%), P = 0.028], lower rate of major complications [6 (7.8%) vs 17 (22.1%), P = 0.011], smaller residual peak systolic gradient at the obstruction level [7.0 (5.0-9.0) vs 11.0 (7.0-16.0) mmHg, P < 0.001]. During the long-term follow-up, it was noted for group 2PSM as compared to group 1PSM: lower 5-year cumulative incidence of major adverse cardiovascular events [3.8% (95% confidence interval 0.7-11.7%) vs 16.9% (9.5-26.1%), P = 0.007] and cardiac-related death [3.8% (95% confidence interval 0.7-11.7%) vs 13% (95% confidence interval 6.6-21.6%), P = 0.05]. SM based on 3D virtual and printed heart models is more effective than conventional SM.

Mechanical properties and ductility improvement mechanisms of fiber-reinforced biomimetic mineralized composites using sea sand

Biomimetic mineralized composites (BMC) is an emerging green cementing material. However, the application of BMC is limited by brittle failure. This study proposes novel fiber-reinforced biomimetic mineralized composites (FRBMC) with excellent ductility based on the coupling method of fiber reinforcement and biomimetic chemically induced calcium carbonate precipitation (BCICP). Three typical fibers, including polymer fibers (polypropylene fiber, PF), mineral fibers (basalt fiber, BF), and plant fibers (coir fiber, CF), were used to explore the feasibility of application in FRBMC. Accordingly, mechanical properties, pore structures, and microscopic characteristics were assessed through unconfined compressive strength (UCS) test, mercury intrusion porosimetry (MIP) tests, and scanning electron microscopy (SEM). The results show that fiber induces a transition from brittle to ductile failure modes in BMC. PF exhibits the most notable enhancement in residual strength and peak strain, while BF leads to the highest compressive strength. CF can effectively enhance energy absorption after reaching peak stress. Moreover, FRBMC with CF contains a higher quantity of minute pores, while BF can reduce the porosity of FRBMC. The calcium carbonate crystals effectively cement fibers and sand particles, enhancing the ductility of FRBMC through forming various cementing structures. This study investigates the synergistic effect of BCICP and fiber reinforcement, providing valuable guidance for potential practical applications of FRBMC.

Non-contact ultrasonic vibration-assisted laser metal deposition manufacturing Fe-based powder: Numerical simulation and experimental investigation

Fe-based powder was manufactured on 42CrMoA steel substrate using non-contact ultrasonic vibration-assisted(UVA) laser metal deposition(LMD) process with different exciting distances(d), and the temperature field and stress field distribution, microstructure and mechanical properties of the deposited layers were investigated. The results show that the distribution of temperature field was more uniform, especially at the bottom of the molten pool, and the gradient of temperature field decreased. Compared with the condition without UVA, the residual stress peak value of the tensile stress area decreased significantly after UVA applied. When d=80 mm, the peak tensile stress and compressive stress were 90.5 MPa and 72.6 MPa, respectively, which were reduced by 45.6 % and 25.2 % compared with the condition without UVA. The length of the columnar crystals and the region of the columnar crystals decreased at the interface after UVA applied. The application of UVA can significantly improved the microhardness of deposition layer. With the reduction of the residual stress at the interface and the improvement of uniformity, the tensile properties of the deposit were also significantly improved. The highest tensile strength was 1281.3 MPa when d=80 mm, which was 30.12 % higher than that without UVA.

Effect of multiscale fibers and cenospheres on the uniaxial tensile behavior of ultra-high performance concrete subjected to high temperatures

Exposure to high temperatures causes a significant deterioration in the mechanical properties of ultra-high-performance concrete. Considering the characteristics of multiscale defects, it is expected to improve the residual tensile performance of ultra-high-performance concrete by incorporating multiscale fibers (including polyethylene fibers, steel fibers, calcium sulfate whiskers, carbon fibers, and carbon nanotubes). An investigation is conducted to examine the impact of multiscale fibers, CE, and temperature ranging from 25 to 800 °C on several aspects of multiscale fibers ultra-high-performance concrete (MSFUHPC), including first cracking strength and strain, ultimate strength and strain, failure mode, as well as the tensile stress-strain relationship. The results show that above 400 °C, multiscale fibers can enhance the first cracking strength, and the effects of calcium sulfate whiskers and CE on the first cracking strain depend on the temperature and their content. It is found that Steel fibers and CE can enhance the strain-hardening ability, and multiscale fibers and CE can increase the residual tensile strength and peak strain at high temperatures. At room temperature, multi-scale fibers and CE increase the maximum tensile strength and ultimate strain of MSFUHPC by 1.28 and 45.92 times, respectively. Moreover, multiscale fibers can refine the pore structure and reduce the porosity at 800 °C. While CE can decrease the increasing rate of porosity with temperature. Furthermore, the uniaxial tensile stress-strain relationship of MSFUHPC after being subjected to high temperatures is suggested based on experimental results, taking into account the influence of multiscale fibers, CE, and temperature.

Progressive Induction Hardening: Measurement and Alteration of Residual Stresses

Progressive induction hardening is an in-line steel heat treatment method commonly used to surface harden powertrain components. It produces a martensitic case layer with a sharp transition zone to the base material. This rapid process will induce large residual stresses, where a compressive state in the case layer will shift to a tensile state in the transition zone. For fatigue performance, it is important to quantify the magnitude and distribution of these stresses, and moreover how they depend on material and processing parameters. In this work, x-ray diffraction in combination with a layer removal method is used for efficient and robust quantification of the subsurface stress state, which combines electropolishing with either turning or milling. Characterization is done on C45E steel samples that were progressively induction hardened using either a fast or slow (27.5 or 5 mm/s, respectively) scanning speed. The results show that although the hardening procedures will meet arbitrary requirements on surface hardness, case depth and microstructure, the subsurface tensile stress peak magnitude is doubled when using a fast scanning speed. However, the near-surface compressive residual stresses are comparable. In addition, the subsurface tensile residual stress peak is compared with the on-surface tensile stresses in the fade-out zone.

ANALYSIS OF ASYMMETRIC PLASTIC BENDING DEFORMATION OF WELDED TUBE SHEETS AND DERIVATION OF A DAMAGE LAW FOR J SHAPE-C SHAPE -O SHAPE FORMING

The J shape-C shape -O shape (JCO) forming method of sheets for large-diameter longitudinally welded pipes has been widely used to manufacture oil and gas pipelines. The quality of welded pipes formed through the JCO process is directly affected by the accurate control of asymmetric bending springback and damage during the procedure. A finite element model (FEM) for JCO asymmetric bending was constructed to investigate the characteristics of asymmetric plastic bending deformation and the distribution laws of damage in JCO forming. This model was based on a nonlinear mixed hardening Lemaitre damage model coupled with the Quasi-Plastic-Elastic (QPE) model. Then, residual stress, forming shape, and damage degree of crimping, first bending, second bending, and third bending were analyzed. Moreover, the accuracy of the model was experimentally verified. Results demonstrate that, the asymmetric bending deformation process can be divided into five stages, including rigid body rotation phase, full elastic deformation phase, elastic–plastic uncladded deformation phase, elastic–plastic cladded phase, and springback phase. In the first bending, the stress centerline significantly misaligns with the mold centerline. Asymmetry is not evident in the second and third bending stages. Furthermore, the peak residual stress and peak damage can be effectively reduced by a larger punch radius, while the peak damage can be reduced by a larger die span. This study lays a foundation for optimizing the technical parameters of JCO forming. Keywords: JCO forming, asymmetric bending, finite element, QPE model, deformation characteristics

Machine learning-based characterization of friction stir welding in aluminum alloys

This research presents a machine learning (ML) approach that integrates Bayesian theorem to predict residual stress, plastic deformation, and peak temperature in friction stir welding (FSW) of different types of aluminum alloys. The training data was acquired from extensive numerical simulations of FSW conducted across various input parameter configurations. The regression analysis exhibits strong predictive performance for residual stress, peak temperature, and plastic deformation, achieving determination coefficients of 0.969, 0.955, and 0.919, respectively. The high prediction performance of the developed model is primarily attributed to Bayesian optimization, distinguishing it from other conventional ML methods. The results further demonstrate the efficacy of the proposed model in assessing the relevance of input features to prediction efficiency and output targets. For instance, concerning processing parameters, the predictive performance is closely correlated with the significance of preheating, traverse speed, and rotational speed in FSW, compared to welding force and plate thickness. On the other hand, considering material properties, it was observed that the hardness value of aluminum alloys emerged as a crucial predictor in the model so that alloys with moderate hardness values showed greater welding consistency and significantly enhanced prediction accuracy.

Mesoscale modellings of axial compressive failure of geometrically-similar CFST columns at low temperatures

In this paper, a thermo-mechanical sequential coupling mesoscopic simulation method was established and verified, which considered the interaction between steel tube and meso-components of concrete due to the difference in thermal parameters, as well as the low-temperature effect on mechanical parameters. On the basis of heat conduction analysis, the damage evolution and failure mechanism of CFST column under axial compression were subsequently revealed, and the effects of low temperature (20, −30, −60 and −80 °C), cross-section size (160, 320, 480 and 640 mm), width-thickness ratio (27, 36, 53 and 107) and cross-section shape (square and circular) on axial compression performance and the corresponding size effect of CFST columns were quantitatively analysed. Research results show that the low-temperature action can enhance the nominal peak strength and residual strength of CFST column, but weaken the ductility. As the cross-section size increases from 160 to 640 mm, all the nominal peak strength, nominal residual strength and peak strain of circular CFST column decrease with the maximum reductions of 16.2, 28.7 and 16.9%, respectively. Besides, the low-temperature action can enhance the size effect on nominal peak strength of CFST column with the maximum increase of 68.8%. Whether at ambient or low temperature, the size effect on nominal peak strength of square column is stronger than that of circular one. The size effect behaviour on axial compressive peak strength at various temperatures can be also well described by the previous proposed prediction formula. The research results of this paper can provide reference for the engineering application of large-sized CFST columns in the extreme low-temperature environment.

Unconfined mechanical properties and micromechanism of short-age recycled aggregate from road solid waste modified by waterborne polyurethane

In recent years, road waste treatment has become a hot topic, and how to solve and utilize these solid wastes is becoming an interesting research field. In order to explore the mechanical modification effect of waterborne polyurethane (PU) on short age road solid waste recycled aggregate, unconfined compression test and scanning electron microscope test were carried out on samples with different dry density and PU content. The dry density was 1.6 g cm−3, 1.7 g cm−3 and 1.8 g cm−3, and the PU content was 0%, 3%, 4%, 5% and 6%, respectively. The tested results show that, the strength of recycled aggregate (RA) increases with the increase of dry density. PU improves the strength and ductility of recycled aggregate (RA), and the residual strength and peak strength of RA increase with the increase of PU content. The peak strength and residual strength of waterborne polyurethane improved recycled aggregate (WPRA) increase with the increase of dry density, too. Polyurethane forms a three-dimensional network structure by film shape and linear shape, and its network structure can provide cohesion and effectively inhibit the crack propagation of the sample. The results demonstrate that adding appropriate amount of PU can effectively improve the mechanical properties of RA, which provides a technical reference for the recycling of RA.

Experimental investigation of the dynamic mechanical properties of concrete under different strain rates and cyclic loading

To investigate the effects of strain rate and cyclic loading on the mechanical parameters of concrete compressive strength, residual strain, peak strain and elastic modulus, a series of cyclic loading tests over concrete were conducted by setting different numbers of cycles, magnitude factors, and cycle frequencies/periods based on the FST-1000 alpine geotechnical dynamic and static triaxial test system. The quantitative relationships between the mechanical parameters of concrete and the parameters of cyclic loading as well as the strain rate were also proposed. The results show that as the strain rate increases, the concrete compressive strength and elastic modulus increase linearly, while the residual strength and peak strain show a decreasing trend. Under cyclic loading, the compressive strength was quadratically related to each cyclic loading parameter, and the elastic modulus was quadratically related to the cyclic number and magnitude factor. The trend of the concrete compressive strength rate sensitivity undergoes a change at the specific thresholds of 0.145 for the magnitude factor and 1.93 Hz for the frequency. The minimum value of the peak strain rate sensitivity corresponds to the specific thresholds of 6023 for the number of cycles, 0.14 for the magnitude factor, and 1.38 Hz for the frequency thresholds, respectively. Additionally, the enhancement of the elastic modulus rate sensitivity occurs when the number of cycles exceeds 918 or when the magnitude factor surpasses 0.33. The results can provide a theoretical basis for the design of concrete structures and seismic engineering.

A new damage constitutive model for frozen-thawed sandstone under triaxial conditions: Considering the characteristics of pre-peak compaction and post-peak residual strength

The study of the constitutive model under stress loading for rock after undergoing freeze-thaw weathering cycles (FTWCs) treatment has important theoretical significance for the site operation and numerical calculation of rock mass engineering in cold regions. In this work, a series of FTWCs treatment tests of sandstone were carried out, and the evolution characteristics of the T2 spectrum distribution curve for sandstone before and after FTWCs treatment were analyzed utilizing nuclear magnetic resonance (NMR) technology. The schematic diagram of freeze-thaw damage evolution for sandstone was drawn, and the damage evolution mechanism was analyzed. Evolution laws of the stress-strain curves, peak and residual strength, peak and residual strain, and Young's modulus of sandstone under different FTWCs and confining pressures were analyzed by conventional triaxial compression tests. A piecewise constitutive model under triaxial stress loading for sandstone after undergoing FTWCs treatment was established, and the model considered the significant influence of FTWCs on the nonlinear deformation in the compaction stage and residual strength. By introducing error analysis indexes, the proposed model and published models were compared with the experimental data, it was found that the proposed model's performance is better than the published models, which indicated that the proposed model has good performance and strong universality.

Numerical modelling on the influence of repair welding during manufacturing on residual stresses and distortions of T-joints

Related to weld quality, level of imperfections is limited which can result in the need of grinding and repair welding. It results in material removal and additional heat cycles causing superimposed distortions and altering the distribution of residual stresses. The current paper investigates the influence of repair welding using welding simulation. Small-scale T-joint is analysed and used for validating the numerical model based on macrographs and distortion measurements. Furthermore, a parametric numerical analysis is conducted to evaluate the influence of repair welding sequence, heat input, and weld size. The research highlights the significance of welding technology and the importance of avoiding repair welding. Plastic strain increment of approx. 33 % occurred in the analysed T-joint, while von Mises residual stress peak increased approx. 26 % at the weld toe due to rewelding. Rewelding sequence had the most significant impact on final distortions; angular distortions could be tripled or nearly zeroed out. On the other hand, a quasi-linear relationship was evaluated between maximum transverse distortion and rewelding heat input. In addition, maximum von Mises stress peak was approximately 500 MPa on the rewelded side, regardless of the fillet size.

Nonmodel rapid seismic assessment of eccentrically braced frames incorporating masonry infills using machine learning techniques

This study investigates the seismic behavior of eccentrically braced frames (EBFs) taking into account the influence of masonry infill walls using a nonmodel scenario-based machine learning framework. Predicting engineering demand parameters (EDPs) by exploiting data-driven approaches and developing the associated fragility curves of infilled EBFs are the main objectives of this research. To this end, a set of 4- and 8-story archetype EBF structures considering 12 distinct infill properties, a total number of 4 bare and 48 infilled EBF models, are created in OpenSees software. A nonlinear pushover analysis is then conducted to assess the overall impact of infills on 4- and 8-story EBFs. Incremental dynamic analysis under 44 far-field ground motions is performed to collect an extensive raw database consisting of 37,164 and 461,480 data points for each variable of bare and infilled EBFs, respectively. It encompasses seismic intensity measure (Saavg), wavelet-based robust damage sensitive feature (rDSF), derived from roof absolute acceleration, frame geometric information, and infill parameter as input features and also EDPs containing peak and residual story drift ratios and peak floor accelerations (PFA) as response variables. After data preprocessing, both regression analysis and machine learning (ML) techniques are utilized to estimate EDPs under two scenarios of Input-Output and Output-Only based on the availability of Saavg. Comparing error measures, particularly in the Extreme Gradient Boosted Tree (ExGBT) algorithm, reveals strong observed-predicted EDP compatibility. Linear equations from bare frame data predict infilled frame EDPs without modification coefficients. Data preprocessing demonstrates that infills decrease drift-based EDPs due to stiffness improvement, while their impact on PFA remains inconclusive. Saavg and rDSF-based fragility curves at three damage states show accurate predictions and effectively reduce vulnerability in infilled 4-story EBFs. However, infills undesirably affect non-ductile behavior in 8-story EBFs, leading to increased global damage as supported by pushover analysis.

Evaluation of impact response of thermal-damaged FRP-RC slabs: Effects of FRP bar type and concrete cover thickness

The purpose of present study is to investigate the impact response of FRP-RC slabs under elevated temperatures. Considering the high-temperature degradation effect and strain rate enhancement effect of FRP bars and concrete materials, a numerical model for studying the fire and impact resistance of FRP-RC slabs was established and verified. The impact failure mechanism of in-fire thermal-damaged FRP-RC slabs was analyzed. The influence of the type of FRP bars, concrete cover thickness and fire duration on the in-fire impact resistance of FRP-RC slabs was revealed. Ultimately, the post-fire residual bearing capacity of the slabs after elevated temperature and impact was obtained. The results show that the typical local punching failure mode is not affected by thermal damage while energy dissipated by concrete accounts for most of the impact energy absorbed by the slabs. When exposed to fire for 60 min, the elevated temperature significantly deteriorates the impact resistance of FRP-RC slabs with a cover thickness of 15 mm. At this time, the greater the concrete cover thickness, the better the impact resistance of FRP-RC slabs. Under the combined action of elevated temperature and impact, Carbon FRP-RC slabs have greater stiffness, lower deflection, greater impact plateau value, less impact duration and lower energy consumption than Aramid FRP, Basalt FRP and Glass FRP-RC slabs. Moreover, the damage index of the slab based on residual bearing capacity and peak displacement is approximately linearly positively correlated. The influence of the concrete cover thickness is more prominent on the damage index based on the peak displacement.

Grinding burn classification with surface Barkhausen noise measurements

Industrial Barkhausen noise (BN) measurements are commonly utilized for final quality control after machining operations such as grinding to point out grinding burns. Grinding burns might compromise the final use and fatigue lifetime of the ground component. The industrial BN method itself is based on a pre-determined threshold value of the BN rootmean-square value (RMS). Elevated RMS values indicate detrimental changes in the component. Usually, the evaluation of grinding burn severity is not carried out. In this study, real ground cylindrical samples were collected that were rejected based on an industrial quality control with a BN unit. A more detailed BN analysis was carried out for 41 individual grinding burn locations followed by X-ray diffraction based residual stress (RS) surface measurements and residual stress and diffraction peak full-width-at-halfmaximum (FWHM) depth profiles. K-means clustering was applied to profiles to label the data points related to grinding burns of different severity. Three classes of grinding burns were identified and verified by micrographs and hardness. A linear discriminant classification model was then identified between the surface BN measurement features and labeled data points. The classification results were reasonable with about 80 % classification accuracy at worst. They showed that the classes identified can be detected with the surface BN measurements. Thus, the approach presented in this paper shows great potential in the practical use of BN measurement where grinding burns can be detected and evaluated with a surface BN measurement.

Experimental and mesoscale analysis on wave propagation induced by impact in dry silica sand

When investigating the propagation of stress waves in sand-like materials, the materials are generally modeled as homogeneous parts despite their complex structures comprising numerous particles of varying sizes and shapes. However, this approach fails to consider the non-continuum nature of sand-like materials. To address this issue, a mesoscale numerical model of silica sand particles with random shapes and three sizes is employed in this study to numerically analyze wave propagation. Experimental data from an upgraded split Hopkinson pressure bar test are utilized to validate the accuracy of the numerical model. Using the validated numerical model, we investigate the impact of relative densities, incident wavelengths, and wave amplitudes on stress wave attenuation in dry silica sand. Empirical equations are derived from summarizing the stress wave attenuation law induced by impact loading. The study shows that relative density and wavelength are critical factors affecting the residual peak stress ratio in silica sand, while the effect of loading wave amplitude is limited.

Quantification of Cerebral Glucose Concentrations via Detection of the H1-α-Glucose Peak in 1 H MRS at 7 T.

Sensitive detection and quantification of cerebral glucose is desired. To quantify cerebral glucose by detecting the H1-α-glucose peak at 5.23 ppm in 1 H magnetic resonance spectroscopy at 7 T. Prospective. Twenty-eight non-fasted healthy subjects (aged 20-28 years). Short echo time stimulated echo acquisition mode (short-TE STEAM) and semi-localized by adiabatic selective refocusing (semi-LASER) at 7 T. Single voxel spectra were obtained from the posterior cingulate cortex (27-mL) using a 32-channel head coil. The H1-α-glucose peak in the spectrum with retrospective removal of the residual water peak was fitted using LCModel with a glucose basis set of only the H1-α-glucose peak. Conventional spectral analysis was performed with a glucose basis set of a full spectral pattern of glucose, also. Fitting precision was evaluated with Cramér-Rao lower bounds (CRLBs). The repeatability of glucose quantification via the semi-LASER sequence was tested. Paired or Welch's t-test were used for normally distributed values. A P value of <0.05 was considered significant. The repeatability of measures was analyzed using coefficient of variation (CV). Removal of the residual water peak improved the flatness and stability of baselines around the H1-α-glucose peak and reduced CRLBs for fitting the H1-α-glucose peak. The semi-LASER sequence was superior to the short-TE STEAM in the higher signal-to-noise ratio of the H1-α-glucose peak (mean ± SD 7.9 ± 2.5, P < 0.001). The conventional analysis overfitted the H1-α-glucose peak. The individual CVs of glucose quantification by detecting the H1-α-glucose peak were smaller than the corresponding CRLBs. Cerebral glucose concentration is quantitated to be 1.07 mM by detecting the H1-α-glucose peak in the semi-LASER spectra. Despite requiring long scan times, detecting the H1-α-glucose peak allows true glucose quantification free from the influence of overlapping taurine and macromolecule signals. 2 TECHNICAL EFFICACY STAGE: 1.

The Different Welding Layers and Heat Source Energy on Residual Stresses in Swing Arc Narrow Gap MAG Welding.

In this paper, in order to reduce the time cost of prediction experiments in industry, a new narrow gap oscillation calculation method is developed in ABAQUS thermomechanical coupling analysis to study the distribution trend of residual weld stresses in comparison with conventional multi-layer welding processes. The blind hole detection technique and thermocouple measurement method verify the reliability of the prediction experiment. The results show that the experimental and simulation results have a high degree of agreement. In the prediction experiments, the calculation time of the high-energy single-layer welding experiments is 1/4 of the traditional multi-layer welding. Two welding processes of longitudinal residual stress and transverse residual stress distribution trends are the same. The high-energy single-layer welding experiment stress distribution range and transverse residual stress peak are smaller, but the longitudinal residual stress peak is slightly higher, which can be effectively reduced by increasing the preheating temperature of the welded parts. This implies that in the specific case of increasing the initial temperature of the workpiece, the use of high-energy single-layer welding instead of multi-layer welding to study the residual stress distribution trend not only optimizes the weld quality but also reduces the time cost to a large extent.

How flexible electrification can integrate fluctuating renewables

To phase out fossil fuels, energy systems must shift to renewable electricity as the main source of primary energy. In this paper, we analyze how electrification can support the integration of fluctuating renewables, like wind and PV, and mitigate the need for storage and thermal backup plants. Using a cost-minimizing model for system planning, we find substantial benefits of electricity demand in heating, transport, and industry adapting to supply. In Germany, flexible demand halves the residual peak load and the residual demand and reduces excess generation by 80%. Flexible operation of electrolyzers has the most significant impact accounting for 42% of the reduction in residual peak load and 59% in residual demand. District heating networks and BEVs also provide substantial flexibility, while the contribution of space and process heating is negligible. The results are robust to restrictions on the expansion of the transmission grid.