Fatigue crack growth behavior of wire arc additively manufactured 316L austenitic stainless steel

This study investigated the fatigue crack growth (FCG) performance of 316L austenitic stainless steel produced by wire arc additive manufacturing (WAAM) through fatigue tests and fractographic analyses. A total of 11 compact tension (CT) specimens were designed considering three minimum-to-maximum load ratios (R= 0.1, 0.3, 0.5), various load directions (θ = 0°, 30°, 45°, 60°, 90°) and two surface conditions (milled and as-built). Details of specimen fabrication and design as well as fatigue test setup are presented. The Paris’ law material constants of all specimens were derived. The influences of various parameters on the FCG behavior such as crack length development histories and fatigue crack growth rate (FCGR) are discussed. The test results demonstrated that the fatigue crack growth rate increased with the load ratio, and that the specimen with θ = 0°, i.e. load parallel to the welding pass, possessed higher FCGR value than the counterparts characterized by other load directions. The as-built and milled specimens had similar FCG performance. The FCG test results of WAAM 316L austenitic stainless steel obtained in this study were compared against those of 316L steels manufactured by traditional hot-rolling and selective laser melting as well as the predictions by current international standards (BS 7910 and IIW-1823-07). The fractographies of typical CT specimens from macroscopic and microscopic perspectives were analyzed. Transgranular fracture was observed as evidenced by abundant fatigue striations, secondary cracks and dimples

A component-based macro-mechanical model for inter-module connections in steel volumetric buildings

Inter-module connections (IMC) are a research focus closely related to the robustness of steel volumetric buildings (VB). Many IMC have been proposed by numerous researchers and engineers, experimentally tested and numerically studied using finite element models. However, there are insufficient IMC macro models available, which imposes challenges for engineers to construct a global numerical VB model. Hence, this study aims to close the gap with a component-based macro-mechanical model for the macro-modelling of IMC in steel VB. In this paper, a comprehensive IMC database was collected to identify and characterise the active components. Two types of macro-mechanical models (H-shape and Q-shape) consisting of P-V-M links have been proposed and a novel uplifting mechanism has been derived for a typical IMC (bolted tie plate with shear key). The proposed macro-mechanical model and other existing macro-models were then compared with existing pushover experiments from an IMC subassembly. The proposed macro-mechanical model shows a good match to the existing experimental results, and it is adaptable to existing IMC.</p

Structural performance of wire arc additively manufactured duplex stainless steel single-lap shear bolted connections

This paper investigates the structural performance of wire arc additively manufactured ER2209 duplex stainless steel (DSS) single-lap shear bolted connections. A comprehensive test campaign was conducted, involving a total of 43 WAAM ER2209 DSS single shear bolted connections with variations in bolt hole positions, surface conditions (i.e. machined or unmachined) and loading orientations relative to the printing direction. The geometric dimensions of the test specimens were meticulously measured using a non-contact 3D laser scanner prior to tensile tests. Detailed analyses on the observed failure patterns, load-displacement curves and resistances considering both deformation and strength criteria are presented. The effects of bolt hole position, surface condition and loading orientation of the WAAM DSS plate on the structural behavior of the single shear bolted connections are analyzed. Given the absence of specific design rules for WAAM DSS bolted connections, the applicability of existing design rules originally developed for conventionally manufactured carbon/stainless steel bolted connections is examined. The experimentally obtained resistances are compared with predictive resistances derived from the Eurocode 3 (prEN 1993–1-8 and prEN 1993–1-4), the American Specification (ANSI/AISC 370–21), and recent design recommendations proposed in the existing literature. The findings underscore that existing design rules tend to provide rather conservative resistance predictions for WAAM ER2209 DSS single shear bolted connections, particularly when employing the deformation criterion, while the design equations proposed in existing literature yield general conservative and the most accurate resistance predictions in strength criterion.</p

Experimental investigation on double-lap shear behavior of 3D printed austenitic stainless steel bolted connections

This paper presents a comprehensive experimental investigation into the double-lap shear behavior of 3D printed austenitic stainless steel bolted connections, manufactured using wire arc additive manufacturing (WAAM) and ER316L feedstock wire. A total of 43 double shear bolted connections were tested, considering variations in end and edge distances, surface conditions (milled and as-built) and test orientations. Details regarding the manufacturing process, geometric measurements using 3D laser scanning, and tensile connection tests are provided. The key test results, encompassing failure modes, load-deformation curves, and resistances with and without consideration of bolt hole deformation, are reported and discussed. The test results were compared with resistances predicted by existing design rules documented in current American Specifications (AISC 360–22, AISC 370–21 and ASCE 8–22) and the Active Shear Plane-based Method from relevant literature, originally calibrated for conventionally fabricated steel lap-shear connections, in order to to assess their applicability for WAAM austenitic stainless steel connections. The comparison results indicated that the resistance predictions by the aforementioned American Specifications are generally conservative for WAAM 316 L austenitic stainless steel double shear bolted connections when considering bolt hole deformation, with AISC 360–22 being the most accurate. When bolt hole deformation is not a design concern, the Active Shear Plane-based Method was shown to provide the most accurate resistance predictions.</p

Behavior of wire arc additively manufactured 316L austenitic stainless steel single shear bolted connections

This paper aims to investigate the behavior of single shear bolted connections made of wire arc additively manufactured 316L austenitic stainless steel. A set of 44 wire arc additive manufacturing (WAAM) 316L austenitic stainless steel single shear bolted connections were included with consideration of various bolt positions, surface conditions and loading orientations respective to the printing layer direction. The geometric dimensions of the WAAM austenitic stainless steel plates were measured with the assistance of non-contact 3D laser scanning prior to tensile testing. Monotonic tensile tests were carried out to investigate the load-deformation responses, failure patterns and resistances determined by both the deformation and strength criteria of the single shear bolted connections. The effects of geometric and printing parameters on the single shear bolted connections were analyzed. Due to the absence of codified design provisions for WAAM austenitic stainless steel bolted connections, the suitability of the existing design rules originally developed for traditionally manufactured carbon steel and stainless steel bolted connections was examined. Design resistances calculated by the Eurocode 3 (prEN 1993-1-8 and prEN 1993-1-4), the American Specification (ANSI/AISC 370-21) as well as the prevalent design recommendations proposed in existing literature were compared with the obtained experimental results. It is shown that the abovementioned design methods offer conservative predictions for the resistances of WAAM 316L austenitic stainless steel single shear bolted connections. Further study is needed to improve the accuracy of design resistance predictions

Local-distortional interaction in cold-formed steel lipped channel beams under uniform bending: Experimental investigation

This paper describes a test campaign concerning the behavior and strength of cold-formed steel (CFS) lipped channel (LC) beams experiencing local-distortional (L-D) interaction made of G450-G500 high-strength steel grades. This investigation involves the performance of 20 tests on simply supported beams arranged in a “back-to-back” configuration, subjected to four-point major-axis bending and laterally restrained at the loading points. All tested specimens failed in the expected L-D interactive modes and exhibited critical distortional-to-local buckling moment ratios ranging between 1.09 and 1.46 (i.e., prone to “true L-D interaction”). The experiment results obtained and reported consist of beam (i) moment-displacement equilibrium paths, (ii) photos evidencing the evolution of the beam deformed configurations along those equilibrium paths (including the failure modes) and (iii) failure moments − it is found that these results are in good agreement with recently performed numerical simulations. Finally, the experimental failure moments obtained are compared with their estimates provided by the (i) currently codified Direct Strength Method (DSM) strength curves associated with local and distortional failures, and (ii) other available DSM-based design approaches developed to handle L-D interactive failures. This comparison provides solid evidence that the CFS specifications must include a DSM-based design approach able to handle beam L-D interactive failures − the current local and distortional design curves clearly overestimate all the experimental failure moments.The authors gratefully acknowledge the support of M Metal Pte Ltd in Singapore, for supplying the cold-formed steel beam specimens tested at The University of Hong Kong

Regulatory B cells in pregnancy: lessons from autoimmunity, graft tolerance, and cancer

The success of pregnancy is contingent on the maternal immune system recognizing and accommodating a growing semi-allogeneic fetus. Specialized subsets of lymphocytes capable of negative regulation are fundamental in this process, and include the regulatory T cells (Tregs) and potentially, regulatory B cells (Bregs). Most of our current understanding of the immune regulatory role of Bregs comes from studies in the fields of autoimmunity, transplantation tolerance, and cancer biology. Bregs control autoimmune diseases and can elicit graft tolerance by inhibiting the differentiation of effector T cells and dendritic cells (DCs), and activating Tregs. Furthermore, in cancer, Bregs are hijacked by neoplastic cells to promote tumorigenesis. Pregnancy therefore represents a condition that reconciles these fields-mechanisms must be in place to ensure maternal immunological tolerance throughout gravidity to allow the semi-allogeneic fetus to grow within. Thus, the mechanisms underlying Breg activities in autoimmune diseases, transplantation tolerance, and cancer may take place during pregnancy as well. In this review, we discuss the potential role of Bregs as guardians of pregnancy and propose an endocrine-modulated feedback loop highlighting the Breg-Treg-tolerogenic DC interface essential for the induction of maternal immune tolerance.Ruth Marian Guzman-Genuino and Kerrilyn R. Diene

Characterization of Respiratory Systems Among Youth Using Heated Tobacco Products in Hong Kong

Importance Heated tobacco products (HTPs) are promoted as less harmful than combustible cigarettes but epidemiological evidence is scarce, especially in youth. Objective To investigate the associations of persistent respiratory symptoms with HTP use, cigarette use, and dual use among Hong Kong youth. Design, Setting, and Participants This was a territorywide cross-sectional school-based survey conducted from October 2018 to July 2019 using an anonymous questionnaire. Schools were randomly invited from a proportionate stratified sample in all 18 districts of Hong Kong. Poisson regression models using generalized estimating equations yielded adjusted prevalence ratios (APRs) of respiratory symptoms in (1) former and current HTP (vs never) users in the whole sample and stratified by cigarette use status and (2) exclusive HTP and dual users vs exclusive cigarette users. Statistical analysis was performed from October 2020 to March 2021. Exposures Former and current use of cigarettes, HTPs, e-cigarettes, and other tobacco products. Main Outcomes and Measures Respiratory symptoms for 3 consecutive months in the past 12 months

Secondhand smoke exposure (SHS) and health-related quality of life (HRQoL) in Chinese never smokers in Hong Kong

Objective: The evidence on the effect of secondhand smoke (SHS) on Health Related Quality of Life (HRQoL) is limited. We examined the relation between SHS and HRQoL among Chinese in Hong Kong. Methods: Adult never smokers from a probability sample of three cross-sectional waves (2010, 2012, 2013) of The Hong Kong Family and Health Information Trends Survey who completed the Cantonese-version of Short-Form 12 Health Survey Questionnaire (SF12v2) were included in the data analysis conducted in 2014. Models were used to examine associations of SHS with SF12 domains and summary scores of Physical (PCS12) and Mental Component (MCS12) with subgroups analysis by SHS locations. Results: After adjustments, SHS was associated with lower scores on all SF12 domains except physical functioning. PCS12 (regress coefficient=−0.76, 95% CI −1.34 to −0.17) and MCS12 (regress coefficient=−1.35, 95% CI −2.06 to −0.64) were lower in those with SHS exposure than those non-exposed. Those exposed to SHS in outdoor public places had lower scores on most SF12 domains and PSC12 and MCS12. SHS exposure in one's home and workplace was associated with lower scores on role physical, body pain and role emotional while SHS exposure in friends’ homes was additionally associated with lower social functioning and mental health scores. Lower MCS12 was associated with SHS exposure at all locations except one's home. Conclusions: Our study showed that SHS exposure, particularly in outdoor public places, was associated with decreased HRQoL. It can provide new evidence for stronger smoke-free policies on public places and promoting smoke-free homes