Key Engineering Materials Vol. 1011

Abstract: This study was initiated to investigate the material characteristics of binder jet (BJ) manufactured austenitic stainless steel 316L, focusing specifically on the less studied bronze infiltrated version of this material. While BJ technology offers a compelling alternative to the current market leader laser powder bed fusion, all additive manufacturing methods are susceptible to porosity, which adversely affects the fatigue properties of parts, resulting in inferior fatigue life compared to traditionally manufactured counterparts. In this study, we explore the novel application of severe shot peening (SSP) as a post-processing method to enhance fatigue life. Through comprehensive microstructural analysis utilizing EBSD, mechanical properties testing via tensile testing, and fatigue life analysis using flexural bending fatigue testing, we demonstrate that SSP treatment induces surface modification, leading to increased material strength albeit with a trade-off in ductility. Moreover, our findings reveal a significant improvement in the fatigue life of the material. Utilizing SSP, we observed that the fatigue limit of the material more than doubled, surpassing the performance of the sheet metal counterpart of the same material. These results underscore the potential of SSP as an attractive method for property enhancement in additive manufacturing.

Abstract: A novel two step austenitization heat treatment process was conceived to develop ADI with optimum combination of strength, ductility and fracture toughness. This novel heat treatment process involved austenitizing the ductile iron in the lower intercritical temperature range and then raising the temperature to the fully austenitic temperature range followed by austempering in the bainitic temperature range. The resulting microstructure consisted of very fine scale bainitic ferrite, high-carbon austenite and pro-eutectoid ferrite. The proeutectoid ferrite is nucleated because of prior austenitization in the intercritical range which resulted in ADI with high fracture toughness without significantly compromising the strength and ductility. An analytical theory has been developed based upon the nucleation of proeutectoid ferrite and graphite nodules during intercritical austenitization, to explain this physical outcome.

Abstract: This study investigates the bending fatigue strength of ultra-high-strength steel (UHS) steel manufactured using wire arc additive manufacturing (WAAM) technology. Hardness evaluations, conducted in the built direction, demonstrated a remarkable consistency with an average hardness of approximately 292 HV throughout the entire deposited component. Further hardness measurements across printed layers revealed uniformity, indicating a lack of hardness variation within the interlayer region. Macrostructural analysis revealed fine grains characterized by an equiaxed morphology, showcasing a distinctive crystallographic arrangement. This microstructural configuration plays a pivotal role in shaping the mechanical behavior and properties of the material. While a detailed microstructure study was not conducted, the macro-level investigation confirmed the absence of visible pores or defects in the printed material, affirming its structural integrity and resilience. Tensile tests conducted on samples extracted from the WAAM part unveiled anisotropic behavior, with tensile strength in the built direction approximately 35 MPa higher than that in the deposition direction. The maximum yield strength reached an impressive 846 MPa in the built direction. Although the yield strength of WAAM UHS was lower compared to the yield strength promised by the welding wire manufacturer, the differing heat input in the WAAM process accounted for this variation. Fatigue strength of the WAAM UHS steel was significantly better compared to WAAM carbon steel used as reference material. The WAAM UHS sample exhibited a robust fatigue limit of 350 MPa.

Abstract: The design of concrete structures with embedded non-metallic composite reinforcement (FRP) is becoming more widespread. The behavior of statically determinate concrete structures reinforced by this durable material is already widely understood and known. Usage of glass and carbon fiber reinforcement is also included in the new generation of Eurocodes for concrete structures. However, in common practice, we also encounter statically indeterminate structures such as continuous beams or slabs. In the case of traditional steel reinforcement of continuous beams, it is possible to assume a certain redistribution of bending moments and to use the principle of linear elastic analysis with limited redistribution in design. According to ACI 440.1R-15 and the new generation of Eurocode a moment redistribution of internal forces on continuous beams or other statically indeterminate structures reinforced with FRP reinforcement should not be considered, given the lower material stiffness and linear elastic behavior up to failure. However, in reality, a redistribution of internal forces can occur. Based on a limited number of studies and experiments that have been carried out in this area globally, there is a premise that some degree of redistribution of bending moment may occur in FRP reinforced indeterminate structures. The objective of this work is to support this assumption through an analytical study of the behavior of a concrete cross-section reinforced with FRP bars, demonstrating its potential for internal force redistribution. The aim of this paper is to present the results of an analytical study capturing the behavior of a concrete cross-section reinforced with FRP, the determination of the deformation characteristics of such a section, and the possible application of the results to a two-span concrete beam. The main emphasis is placed on the stress-strain diagram of concrete and its influence on deformation characteristics, mainly moment-curvature relationship.

Abstract: The Sweating Slab Syndrome (SSS) was first mentioned in 2005 [3] and has further been discussed in [1], [2], [5], [6]. The condition is typically marked by the build-up of moisture in so-called big-box warehouse buildings on the top surface of concrete slab-on-ground construction which, when severe, can interfere with the routine operations of the facility, e.g. forklift traffic. The buildings are typically located in southern to southeastern regions of the United States and have non-climate controlled indoor environments. After drying, residues remain on the surface of the slab-on-ground, which have been identified as carbonation products of alkaline salts. Speculations as to the cause of this syndrome have included dew-point condensation, high vapor permeability of the slab, the troweling finishing process, bond breaker influence, unreacted silicates from integral or spray applied admixtures, and the absence of vapor retarder sheets under the slab. None of the speculated causes have been given supporting data or studied in detail, however. To determine the cause of the SSS, Wiss, Janney, Elstner, Associates, Inc. (WJE) applied a standard scientific methodology in 2019 consisting of three parts. The first part of this methodology was to collect data through observation, instrumentation, numerical simulation, and laboratory analysis. Second, a set of hypotheses was generated based on the data collection and logic. Finally, collected data was paired with one or multiple hypotheses in a logical way to disprove or support their validity. Results will be shown.

Abstract: The paper examines three different ceiling slab concepts for garages, considering common column spacings (8 × 8 m, 5 × 11.2 m, and 5 × 16.2 m). It provides a comparison between reinforced and post-tensioned concrete slabs, highlighting the advantages of post-tensioned ceilings in terms of maximizing parking spaces and reducing material consumption (concrete and steel). Optimizing space and minimizing material usage are crucial in modern construction to lower CO2 emissions and enhance spatial flexibility.

Abstract: The paper presents the rules for determining the minimum reinforcement in reinforced concrete structures that have been recommended in recent years and currently. It has been analyzed whether the reinforcement in structural members designed in different periods of time on the basis of various standard regulations regarding minimum reinforcement meets the conditions for protecting the structure against brittle failure. The necessary reinforcement has been determined using the method derived on the basis of nonlinear fracture mechanics of concrete. In the performed analysis the scale effect has been taken into account as well.

Abstract: This paper focuses on the multicriteria software optimization of reinforced concrete floor slabs, especially in terms of environmental impacts and cost. The economic aspect is essential to ensure that the environmentally friendly design option is also cost effective. The durability of the structure is also considered as it significantly affects its overall environmental footprint. Increased durability reduces the frequency of repairs and extends the service life before demolition and reconstruction are required, thereby spreading the environmental impacts of the initial construction over a longer period. The software tool used for optimization was developed in previous work, and this paper extends its application to lightweight floor slabs and prestressed hollow core slabs. This extension aims to enhance the practical usability of the optimization algorithm. Lightweight floor slabs, particularly for large spans, can reduce both environmental burdens and construction cost. This paper describes the extension of an optimization algorithm to identify the most advantageous floor design in terms of environmental impact and cost. It also examines the benefits of floor slab lightweighting and provides general recommendations for optimizing reinforced concrete floor slabs.

Abstract: Traditionally, reinforced concrete structures are constructed using steel rebars as reinforcement which is more susceptible to reinforcement corrosion in severe exposure conditions. This leads to many disadvantages, like deterioration of concrete, reduction in strength, and increase in maintenance costs, which leads to a decrease in the serviceability of critical infrastructure. Fiber Reinforced Polymer bars are often used as alternative materials for steel bars because they are anti-corrosive, exhibit an excellent strength-to-weight ratio and are easy to handle but the main disadvantage is its brittle nature. Hence, the combination of steel and FRP bars was effectively used to augment both flexural capacity and ductility. As the ductility performance of hybrid Reinforcement is lower than conventional reinforced beams, Polyvinyl Alcohol Fibers in volume fraction were added in this investigation. The present investigation aims to determine the flexural capacity of reinforced concrete beams using Glass Fiber Reinforced Polymer (GFRP) bars and Steel bars. The optimum dosage of PVA fibers while evaluating compressive and split tensile strength is observed at 0.25% in volume fraction. Total six types of concrete beam specimens with and without PVA fibers were experimentally under four-point bending test tested such as beams reinforced with only steel bars, only GFRP bars, GFRP and steel bars. From the experimental results, it is observed that inclusion of PVA fibers in proposed beams with hybrid reinforcement enhanced the crack resistance by 80% and ultimate load capacity by 39% when compared with conventional beam.