Monitoring and characterization of abnormal process conditions in resistance spot welding

Resistance spot welding (RSW) is extensively used for sheet metal joining of body-in-white (BIW) structure in the automobile industry. Key parameters, such as welding current, electrode force and welding time, are involved in the RSW process. Appropriate welding parameters are vital for producing good welds; otherwise, undersized weld and expulsion are likely to be caused. For a specific type of sheet metal, an acceptable nugget is produced when an appropriate combination of welding parameters is used. However, undersized welds and expulsion are still commonly seen in the plant environment, where some abnormal process conditions could account for the production of the poor quality welds. Understanding the influence of abnormal process conditions on spot weld quality and other RSW related issues is crucial. A range of online signals, strongly related to the nugget development history, have attracted keen interest from the research community. Recent monitoring systems established the applied dynamic resistance (DR) signal, and good prediction of nugget diameter was made based on signal values. However, the DR curves with abnormal process conditions did not agree well with those under normal condition, making them less useful in detecting abnormal process conditions. More importantly, none of the existing monitoring systems have taken these abnormal process conditions into account. In addition, electrode degradation is one of the most important issues in the plant environment. Two major electrode degradation mechanisms, softening and intermetallic compound (IMC) formation, are strongly related to the characteristics of welding parameters and sheet metals. Electrode misalignment creates a very distinct temperature history of the electrode tip face, and is believed to affect the electrode degradation mechanism. Though previous studies have shown that electrode misalignment can shorten electrode life, the detailed mechanism is still not understood. In this study, an online-monitoring system based on DR curve was first established via a random forest (RF) model. The samples included individual welds on the tensile shear test sample and welds on the same sheet, considering the airgap and shunting effect. It was found that the RF model achieved a high classification accuracy between good and poor welds. However, the DR signals were affected by the shunting distance, and they displayed opposite trends against individual welds made without any shunting effect. Furthermore, a suitable online signal, electrode displacement (ED), was proposed for monitoring abnormal process conditions such as shunting, air gap and close edged welds. Related to the thermal expansion of sheet metal, ED showed good consistency of profile features and actual nugget diameters between abnormal and normal welds. Next, the influence of electrode misalignment on electrode degradation of galvannealed steel was qualitatively and quantitatively investigated. A much-reduced electrode life was found under the angular misalignment of 5°. Pitting and electrode softening were accelerated on the misaligned electrodes. δ Fe-Zn phase from the galvannealed layer that extends electrodes was found non-uniformly distributed on the worn electrode. Furthermore, electron backscatter diffraction (EBSD) analysis was implemented on the worn electrode, showing marked reduction in grain diameter and aspect ratio. The grain deformation capacity was estimated by the distribution of the Taylor factor, where the portion of pore grain was substantially weakened in the recrystallized region compared to the base metal region

Characteristics of shunting effect in resistance spot welding in mild steel based on electrode displacement

Shunting effect of resistance spot welding is evaluated based on the electrode displacement signals. The shunted welds in mild steel with different weld spacing were produced. The results showed that the weld spacing and nugget diameter were polynomial-correlated, and the minimum welding spacing of 20 mm can be derived from the results. Both the peak value and gradient of electrode displacement in the weld stage indicated strong correlations with the nugget diameters of shunted welds. Additional shunt path was found to further aggregate the shunting, suggesting the decline in the values of profile features. Furthermore, it is found that the shunting effect led to the decline of the dynamic resistance curves, which is contradictive to the trends between acceptable-sized and undersized welds claimed based on the single weld study. The paper shows that electrode displacement curves of shunting can be incorporated into existing quality monitoring system.The financial support from the Australian Research Council (Grant No. LP130101001) is fully acknowledged

Deformation mechanism of kink-step distorted coherent twin boundaries in copper nanowire

In the construction of nanotwinned (NT) copper, inherent kink-like steps are formed on growth twin boundaries (TBs). Such imperfections in TBs play a crucial role in the yielding mechanism and plastic deformation of NT copper. Here, we used the molecular dynamic (MD) method to examine the influence of kink-step characteristics in depth, including kink density and kink-step height, on mechanical behavior of copper nanowire (NW) in uniaxial tension. The results showed that the kink-step, a stress-concentrated region, is preferential in nucleating and emitting stress-induced partial dislocations. Mixed dislocation of hard mode I and II and hard mode II dislocation were nucleated from kink-step and surface atoms, respectively. Kink-step height and kink density substantially affected the yielding mechanism and plastic behavior, with the yielding stress functional-related to kink-step height. However, intense kink density (1 kink per 4.4 nm) encourages dislocation nucleation at kink-steps without any significant decline in tensile stress. Defective nanowires with low kink-step height or high kink density offered minimal resistance to kink migration, which has been identified as one of the primary mechanisms of plastic deformation. Defective NWs with refined TB spacing were also studied. A strain-hardening effect due to the refined TB spacing and dislocation pinning was observed for defective NWs. This study has implications for designing NT copper to obtain optimum mechanical performance.This research was undertaken with the assistance of resources from the National Computational Infrastructure (NCI), which is supported by the Australian Government. This work was supported by the Australian Research Council under Grant Nos. LP130101001

The Euscaphis japonica genome and the evolution of malvids

Malvids is one of the largest clades of rosids, includes 58 families and exhibits remarkable morphological and ecological diversity. Here, we report a high-quality chromosome-level genome assembly for Euscaphis japonica, an early-diverging species within malvids. Genome-based phylogenetic analysis suggests that the unstable phylogenetic position of E. japonica may result from incomplete lineage sorting and hybridization event during the diversification of the ancestral population of malvids. Euscaphis japonica experienced two polyploidization events: the ancient whole genome triplication event shared with most eudicots (commonly known as the c event) and a more recent whole genome duplication event, unique to E. japonica. By resequencing 101 samples from 11 populations, we speculate that the temperature has led to the differentiation of the evergreen and deciduous of E. japonica and the completely different population histories of these two groups. In total, 1012 candidate positively selected genes in the evergreen were detected, some of which are involved in flower and fruit development. We found that reddening and dehiscence of the E. japonica pericarp and long fruit-hanging time promoted the reproduction of E. japonica populations, and revealed the expression patterns of genes related to fruit reddening, dehiscence and abscission. The key genes involved in pentacyclic triterpene synthesis in E. japonica were identified, and different expression patterns of these genes may contribute to pentacyclic triterpene diversification. Our work sheds light on the evolution of E. japonica and malvids, particularly on the diversification of E. japonica and the genetic basis for their fruit dehiscence and abscission.DATA AVAILABILITY STATEMENT : All sequences described in this manuscript have been submitted to the National Genomics Data Center (NGDC). The raw whole-genome data of E. japonica have been deposited in BioProject/GSA (https://bigd.big.ac.cn/gsa.) under the accession codes PRJCA005268/CRA004271, and the assembly and annotation data have been deposited at BioProject/GWH (https://bigd.big.ac.cn/gwh) under the accession codes PRJCA005268/GWHBCHS00000000. The raw transcriptomes data of E. japonica have been deposited in BioProject/GSA (https://bigd.big.ac.cn/gsa.) under the accession codes PRJCA005298/CRA004272.SUPPLEMENTARY MATERIAL 1: Supplementary Note 1. Chromosome number assessment. Supplementary Note 2. Whole-genome duplication identification and dating. Supplementary Note 3. Observation of E. japonica seed dispersal. Supplementary Note 4. Determination of pentacyclic triterpene substances. Figure S1. Cytogenetic analysis of E. japonica. Figure S2. Genome size and heterozygosity of E. japonica estimation using 17 k-mer distribution. Figure S3. Interchromosomal of Hi-C chromosome contact map of E. japonica genome. Figure S4. Gene structure prediction results of E. japonica and other species. Figure S5. Venn diagram shows gene families of malvids. Figure S6. Phylogenetic tree constructed by chloroplast genomes from 17 species. Figure S7. Concatenated- and ASTRAL-based phylogenetic trees. Figure S8. Ks distribution in E. japonica. Figure S9. Distributions of synonymous substitutions per synonymous site (Ks) of one-to-one orthologs identified between E. japonica and P. trichocarpa and V. vinifera. Figure S10. Population structure plot. Figure S11. Fixation index (FST) heat map among E. japonica populations. Figure S12. Phylogenetic analysis of MADS-box genes from O. sativa, A. thaliana, E. japonica, and T. cacao. Figure S13. Observation the fruit development. Figure S14. Animal seed dispersal. Figure S15. Anthocyanin biosynthesis in E. japonica fruits. Figure S16. Carotenoid accumulation and the chlorophyll degradation in E. japonica fruits. Figure S17. Expression profile of fruit dehiscence-related genes. Figure S18. Phylogenetic tree of DELLA genes obtained from six malvids species. Figure S19. Phylogenetic tree of CAD genes obtained from seven malvids species. Figure S20. Expression pattern of fruit abscission-related genes. Figure S21. Structure of pentacyclic triterpene compounds separated from Euscaphis. Figure S22. Phylogenetic tree of HMGR gene in plants. Figure S23. Phylogenetic tree of P450s gene family obtained from A. thaliana and E. japonica.SUPPLEMENTARY MATERIAL 2: Table S1. Assembled statistics of E. japonica genome. Table S2. Evaluation of E. japonica genome assembly. Table S3. Chromosome length of E. japonica. Table S4. Prediction of gene structures of the E. japonica genome. Table S5. Statistics on the function annotation of the E. japonica genome. Table S6. Non-coding RNA annotation results of E. japonica genome. Table S7. BUSCO assessment of the E. japonica annotated genome. Table S8. Statistic of repeat sequence in E. japonica genome. Table S9. Gene-clustering statistics for 17 species. Table S10. KEGG enrichment result of unique genes families of E. japonica. Table S11. Gene Ontology (GO) and KEGG enrichment result of significant shared by malvids species gene families. Table S12. Gene Ontology (GO) and KEGG enrichment result of significant expansion of E. japonica gene families. Table S13. Gene Ontology (GO) enrichment result of significant contraction of E. japonica gene families. Table S14. Statistical sampling population information. Table S15. Statistics population resequencing information. Table S16. Statistical nucleotide polymorphisms in the populations. Table S17. Candidate positive selection genes (PSGs) in the evergreen population. Table S18. Candidate positive selection genes (PSGs) in the deciduous population. Table S19. Gene Ontology (GO) enrichment result of significant PSGs in the evergreen population. Table S20. List of MADS-box genes identified in E. japonica. Table S21. Genes involved in anthocyanin biosynthesis, carotenoid biosynthesis, and chlorophyll degradation. Table S22. Identification fruit dehiscence-related genes in E. japonica. Table S23. Genes related to lignin synthesis that are highly expressed during pericarp dehiscence. Table S24. Gene expression levels (FPKMs) of fruit abscission-related genes in pericarp. Table S25. Triterpene compounds separated from Euscaphis. Table S26. Number of putative pentacyclic triterpene-related genes in the malvids species. Table S27. Identified pentacyclic triterpene synthesis-related genes in E. japonica genome. Table S28. Statistical simple sequence repeat.Fund for Excellent Doctoral Dissertation of Fujian Agriculture and Forestry University, China; Fujian Provincial Department of Science E. japonica Evolution and Selection of Ornamental Medicinal Resources, China; the Project of Forestry Peak Discipline at Fujian Agriculture and Forestry University, China; the Collection, Development and Utilization of Eascaphis konlshli Germplasm Resources; the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation program and from Ghent University.https://onlinelibrary.wiley.com/journal/1365313xam2022BiochemistryGeneticsMicrobiology and Plant Patholog

Effect of Interface on the Deformation of Aluminium Bicrystal: Atomistic Simulation Study

Molecular dynamic (MD) simulation has been conducted to study the effect of interface structure on the mechanical response of eight symmetric tilt grain boundaries in high stacking-fault Al. It is found that the grain boundaries with E structure unit (SU) have higher energy, but the grain boundary energy alone cannot be used as a parameter to determine the mechanical properties of grain boundary. The SUs, especially E units, do have an influence on the mechanical response of grain boundaries. Our results show that the dislocation imitates from E units preferably, but this depends on the dissociation at grain boundary

Effect of Interface on the Deformation of Aluminium Bicrystal: Atomistic Simulation Study

Molecular dynamic (MD) simulation has been conducted to study the effect of interface structure on the mechanical response of eight symmetric tilt grain boundaries in high stacking-fault Al. It is found that the grain boundaries with E structure unit (SU) have higher energy, but the grain boundary energy alone cannot be used as a parameter to determine the mechanical properties of grain boundary. The SUs, especially E units, do have an influence on the mechanical response of grain boundaries. Our results show that the dislocation imitates from E units preferably, but this depends on the dissociation at grain boundary

Deformation mechanism of kink-step distorted coherent twin boundaries in copper nanowire

In the construction of nanotwinned (NT) copper, inherent kink-like steps are formed on growth twin boundaries (TBs). Such imperfections in TBs play a crucial role in the yielding mechanism and plastic deformation of NT copper. Here, we used the molecular dynamic (MD) method to examine the influence of kink-step characteristics in depth, including kink density and kink-step height, on mechanical behavior of copper nanowire (NW) in uniaxial tension. The results showed that the kink-step, a stress-concentrated region, is preferential in nucleating and emitting stress-induced partial dislocations. Mixed dislocation of hard mode I and II and hard mode II dislocation were nucleated from kink-step and surface atoms, respectively. Kink-step height and kink density substantially affected the yielding mechanism and plastic behavior, with the yielding stress functional-related to kink-step height. However, intense kink density (1 kink per 4.4 nm) encourages dislocation nucleation at kink-steps without any significant decline in tensile stress. Defective nanowires with low kink-step height or high kink density offered minimal resistance to kink migration, which has been identified as one of the primary mechanisms of plastic deformation. Defective NWs with refined TB spacing were also studied. A strain-hardening effect due to the refined TB spacing and dislocation pinning was observed for defective NWs. This study has implications for designing NT copper to obtain optimum mechanical performance

Quality assessment of resistance spot welding process based on dynamic resistance signal and random forest based

A scheme for online quality monitoring of resistance spot welding (RSW) process is proposed to effectively determine the rate of spot weld quality. In this work, the random forest (RF) classification featuring with dynamic resistance (DR) signals which were collected and processed in the production environment was carried out. The obtained results demonstrated that the constructed RF model based on DR profile features adequately distinguished high-quality welds from the other unacceptable welds such as inadequate sized welds and expulsions. Variable importance evaluation of RF was implemented against the input features. It showed that two DR slopes for nugget nucleation and growth (v 2 , v 3 ) and dynamic resistance (R γ ) in the final half cycle play the most significant roles in achieving more accurate results of classification, while absolute gradient ∇ max is useful in detecting minor expulsion from pull-out failure. In addition, shunting effect in consecutive welds was tentatively investigated via the DR curves, accounting for noticeable declines in the stage I of DR. The results revealed that shunted welds beyond minimum weld spacing do not significantly undermine the accuracy of classification. The implementation of RF based on the combination of welding parameters and DR features improves the accuracy of classification (98.8%) with ntree = 1000 and mtry = 4, as weld current significantly distinguished situations where DR features solely achieve accuracy (93.6%). The incorporation of the RF technique into online monitoring system attains a satisfying RSW quality classification accuracy and reduces the workload on destructive tests.This study was funded by Australian Research Council (Grant No. LP130101001)

Qualitative and quantitative analysis of misaligned electrode degradation when welding galvannealed steel

Electrode misalignment, induced from the flexibility of welding machine gun of spot welder or the potential poor fit-up, leads to the high tendency of expulsion and asymmetric nugget shape. Yet very few studies have focused on the influence of misalignment on the electrode degradation and microstructure evolution of the electrode, especially when welding galvannealed steel. This paper investigates the degradation of such misaligned electrodes when spot welding galvannealed steel. To reveal its mechanism, the electrodes welded with galvannealed steel were examined after 10 and 200 welds with the slight misalignment. The electrodes were found to experience more severe degradation compared to the results from previous studies with the aligned electrodes. The results from energy-dispersive spectrum (EDS) analysis further confirmed that δ-Fe–Zn phase, a barrier from galvannealed coating for isolating Cu and Zn formation, was not uniformly distributed on the electrode tip. As a result, the initial electrode pitting took place after 50 welds. Furthermore, electron backscatter diffraction (EBSD) quantitatively analyzed the recrystallized grains of the worn electrodes, which underwent rotation under the asymmetric pressure distribution under misalignment. The calculated Taylor factor via EBSD mapping also indicated the declined portion of grains accounted for the low deformation resistance of the worn electrode. Finally, electrode displacements were simultaneously collected in the experiments, of which the peak values accurately predicted the heat generation for each spot weld and accordingly predicted the electrode life.The financial support from the Australian Research Council (Grant No. LP130101001) is fully acknowledged