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Self-piercing riveting (SPR) has been used to join similar and dissimilar materials for vehicle body application. In order to understand the failure mechanism and develop a method to estimate the shear strength of SPR similar and dissimilar materials, finite element modeling was conducted in this study. In the modeling, the contact conditions between the rivet and the workpieces were taken into account to establish the failure criteria of SPR of steel and aluminum sheets. It was found that the failure procedure of riveted dissimilar materials was different from that of riveted similar materials. Furthermore, the experiments were conducted to validate the modeling results. It was shown that the shear strength and failure mode of SPR joints were in agreement with the modeling results. These results suggested that the model could be used to estimate the shear strength of SPR joints. The factors influencing the failure mode and shear strength of SPR joints were discussed in detail. For rivet pull-out mode, the rivet open angle at the upper sheet, friction coefficient between the rivet and sheet, and the yield strength of the substrate were the key factors. For sheet tearing mode, failure occurred at the weaker sheet and the shear strengths mainly depended on the sheet gage and strength grade of the weaker sheet. [ABSTRACT FROM AUTHOR]

In this paper, the strength development of a pure steel slag (SS) system with various concentrations of N,N,N′,N′-Tetrakis-(2-hydroxyethyl) ethylenediamine (THEED) was investigated. The hydration kinetics, pore structure and microstructure of SS pastes with and without THEED were characterized to underscore the working mechanism of THEED. Results show that THEED additions significantly increase the 3, 7 and 28 days compressive strength of hardened SS pastes. The enhancement effect increases with the dosage of THEED. At a concentration of 2000 ppm, THEED increased the compressive strength by 733%, 665%, and 545% at 3, 7 and 28 days, respectively. It is confirmed that THEED additions improve the hydration degree of SS by accelerating hydration of the aluminum phase (C3A, PDF-38-1429; C12A7, PDF-48-1882) and C2F,(PDF 38-0408) to generate Mc (PDF-41-0219) and Pa (PDF-30-0222) in the presence of CaCO3. Also, the hydration degree of silicates is increased by THEED. In this way, THEED additions refine the pore structure of hardened SS paste by increasing the pore volume with a diameter below 300 nm to achieve enhancement. The chelating effect of THEED results in promoting dissolution of SS, which provides the driving force for accelerating SS hydration. [ABSTRACT FROM AUTHOR]

Laser powder bed fusion (LPBF) allows the fabrication of complex parts with high resolution. In the process of manufacturing complex parts, overhanging structures with unique mechanical properties are inevitable. The mechanical properties are relevant to the microstructure that are severely influenced by the support structures and build orientation. In this study, a three-dimensional finite element model was established to numerically investigate the thermal behavior of the melt pool in the overhanging structures, and the effects of different forming conditions on tensile behavior were analyzed through the microstructure of overhanging specimens and fracture surfaces of failed specimens. The simulation results show that the change trend of the melt pool size is the same as that of the maximum temperature. Moreover, the melt pools closer to the down-facing surface of overhanging structures carry higher temperature and larger size. The application of the support structures effectively reduces the temperature of the melt pool in the starting layer by 5.3%. With the increase of inclination angle, the melt pool temperature in the starting layer decreases slightly. The experimental results indicate that the mechanical properties of 45° specimens fabricated above the entity are stronger than those of 45° specimens with support structures, and the mechanical properties of 45° specimens with support structures are stronger than those of 45° specimens without support structures. Moreover, the mechanical properties of the specimens deteriorate when the build orientation of the overhanging structures varies from 0° to 45°. The mechanical properties of different specimens with 45° build orientation are mainly affected by the thickness of defect area, and the mechanical properties of the specimens with different build orientations are mainly affected by fracture path. The results will facilitate the understanding and application of the LPBF manufacturing technique for overhanging structures in complex parts. [ABSTRACT FROM AUTHOR]

• The design method of hierarchical structure is proposed. • The proposed hierarchical structure has a dual function of stretching and bending. • The specific component ratio and size ratio can enhance energy absorption. With the development of additive manufacturing technology, lattice structures with complex topological shapes can be manufactured. In order to combine the advantages of stretch dominance and bend dominance, a hierarchical lattice structure composed of variable unit cell is proposed. The hierarchical lattice structures are manufactured by laser powder bed fusion (LPBF). Five different cell arrangement combinations are designed based on face centered cubic (FCC) with octet truss structure (OTS) at the macro scale. The mechanical performance and deformation behavior of the hierarchical lattice was investigated systematically through compressive experiments and numerical simulations. The deformation modes were captured with a digital camera. Then, the crashworthiness design on the Row layered structure parametric analysis was performed to discuss the effect of geometrical parameters including component ratio and size ratio. The results indicated that the hierarchical structure exhibits a mixed deformation mode among those the Row layered structure has the best energy absorption characteristics. And the specific ratios of these geometrical parameters significantly enhance the energy absorption of hierarchical structure. Overall, this work not only provides a novel solution for designing hierarchical structures, but also highlights the advantages of additive manufacturing techniques for manufacturing complex structures. [ABSTRACT FROM AUTHOR]

Triply periodic minimal surfaces (TPMSs) are extensively used as effective tools for the microarchitectural designing of cellular structures. CoCrNi medium-entropy alloy, known for its high strength and high ductility, is an ideal candidate for fabricating TPMS-based structures. However, few studies have focused on this topic. This study investigated the compressive mechanical and energy absorption properties of CoCrNi D-sheet TPMS cellular structures fabricated via selective laser melting (SLM). The surface morphology of the fabricated D-sheet TPMS structure was observed through scanning electron microscopy, and the deformation and failure mechanisms of the structure were analyzed by the quasi-static compression test. The results indicated that the SLM-ed CoCrNi D-sheet TPMS structure exhibited stable collapse mechanisms compared to other metal-based TPMS structures. Meanwhile, the energy absorption characteristics of the modified finite element (FE) model agreed well with the experimental results. Furthermore, the impact of the level constant on the energy absorption performance of the D-sheet TPMS structure was investigated using the FE model. Thus, an optimal D-sheet (OD-sheet) TPMS structure with lower density and higher energy absorption capacity was obtained. Additionally, the Gibson–Ashby prediction model was established to aid in selecting CoCrNi OD-sheet TPMS structures with controlled relative densities for energy absorption applications. [Display omitted] • CoCrNi D-sheet TPMS cellular structures were fabricated via selective laser melting. • SLM-ed CoCrNi D-sheet TPMS structure exhibited stable collapse mechanisms. • Optimal D-sheet TPMS structure with high energy absorption capacity was obtained. [ABSTRACT FROM AUTHOR]

This work aims to investigate the solubilizing ability of alkanolamines on steel slag (SS) and the chelating ability of alkanolamines with metal ions. In this paper, the chelation effect of four alkanolamines, including triethanolamine (TEA), triisopropanolamine (TIPA), diethanol-isopropanolamine (DEIPA), and methyl diethanolamine (MDEA), and metal ions on the dissolution of SS was investigated. The conductivity meter, pH meter, X-ray powder diffraction (XRD), inductively coupled plasma atomic emission spectroscopy (ICP-AES), total organic carbon (TOC) and isothermal calorimetry were used to investigate the solubilizing ability of SS impacted by alkanolamines. Additionally, the conductivity meter and chemical precipitation method (CPM) were used to investigate and explore the chelating ability of alkanolamines interacting with the metal ions. Finally, the nuclear magnetic resonance hydrogen (1HNMR) spectroscopy was adopted to investigate the chelating mechanism between alkanolamines and metal ions. The results showed that the alkanolamines increased the elemental concentrations of [Ca], [Al], [Fe] and [Si] in the liquid phase of SS through chelating and promoted the dissolution of the mineral phase of C 3 S, C 2 S and C 4 AF in SS. Among the different alkanolamines, DEIPA was present in the liquid phase for the longest time and possessed a more sustained ability to chelating metal ions. The result also shows that alkanolamines can chelate the Ca2+, Al3+ and Fe3+ in solution. The chelating ability of tertiary alkanolamines were stronger than the secondary alkanolamine. And the alkanolamine with asymmetric molecular structure have stronger chelating ability than those with symmetric molecular structure. Tertiary alkanolamines form ternary five-ring structure with metal ion through nitrogen and oxygen atoms. • Alkanolamines promoted the dissolution of the mineral phase in steel slag. • DEIPA possessed a more sustained ability to chelating metal ions. • Alkanolamine with asymmetric molecular structure have stronger chelating ability. • Ternary five-ring structure formed between the ternary alkanolamine and metal ion. [ABSTRACT FROM AUTHOR]

• The correlation between defects and thermal behavior is discussed, and the forming causes of defects are analyzed. • A physical model is proposed to simulate the thermal behavior of melt pool under different processing parameters. • Processing parameters have significant influence on macroscopic morphology but have little influence on dendrite spacing. Selective laser melting (SLM) is a kind of material forming technology which involves many processing parameters. The appropriate processing parameters are very important to the forming quality of manufactured samples. In this paper, the influence of laser power and scanning speed on the manufacturing defects, thermal behavior and compression properties of AlSi10Mg lattice structures during SLM were systematically investigated. By observing the macroscopic and microscopic morphology of manufactured samples, it was found that the processing parameters had a significant influence on the strut diameter and internal porosity but had little influence on the dendrite spacing and grain size. A physical model considering thermal loss and thermal conduction in temperature field was proposed to simulate the thermal behavior of melt pool under different processing parameters. The results showed that the thermal behavior was more sensitive to the laser power, and the manufacturing defects were related to the transient temperature and dimension of the melt pool. The digital image correlation (DIC) method was adopted to analyze the strain distribution of manufactured lattice during the compression process. Meanwhile, the relationship between processing parameters, thermal behavior and manufacturing defects was discussed in detail. Finally, based on the optimal processing parameters (250 W-1400 mm/s), the accuracy of manufactured lattice structure was verified by finite element method. The research results can provide a reference for the selection of processing parameters for manufacturing AlSi10Mg lattice structure. [ABSTRACT FROM AUTHOR]