Fatigue strengthening of damaged steel members using wire arc additive manufacturing

In this study, a directed energy deposition (DED) process called wire arc additive manufacturing (WAAM) is employed for the fatigue strengthening of damaged steel members. Three steel specimens with central cracks were tested under a high-cycle fatigue loading (HCF) regime: (1) the reference specimen; (2) the WAAM-repaired specimen with an as-deposited profile, and (3) the WAAM-repaired specimen machined to reduce stress concentration factors (SCF). The corresponding finite element (FE) simulation of the WAAM process was calibrated using static experimental results, which revealed the main mechanism. The process was found to introduce compressive residual stresses at the crack tip owing to the thermal contraction of the repair. The FE results also revealed that stress concentration exists at the root of the as-deposited WAAM; this stress concentration can be mitigated by machining the WAAM to a pyramid-like shape. The fractography analysis indicated that the cracks were initiated at the WAAM-steel interface, and microscopic observations revealed that the microcracks were arrested by the porosities in the melted interface. The results of this pioneering study suggest that WAAM repair is a promising technique for combating fatigue damage in steel structures

Multi-dimensional classical and quantum cosmology: Exact solutions, signature transition and stabilization

We study the classical and quantum cosmology of a $(4+d)$-dimensional spacetime minimally coupled to a scalar field and present exact solutions for the resulting field equations for the case where the universe is spatially flat. These solutions exhibit signature transition from a Euclidean to a Lorentzian domain and lead to stabilization of the internal space, in contrast to the solutions which do not undergo signature transition. The corresponding quantum cosmology is described by the Wheeler-DeWitt equation which has exact solutions in the mini-superspace, resulting in wavefunctions peaking around the classical paths. Such solutions admit parametrizations corresponding to metric solutions of the field equations that admit signature transition.Comment: 15 pages, two figures, to appear in JHE

Fatigue testing and analysis of steel plates manufactured by wire-arc directed energy deposition

Wire-arc directed energy deposition (DED), also known as wire-arc additive manufacturing (WAAM), is a metal 3D printing technique that is recognised for its high efficiency, cost-effectiveness, flexibility in build scales and suitability for the construction sector. However, there remains a lack of fundamental data on the structural performance of WAAM elements, especially regarding their fatigue behaviour. A comprehensive experimental study into the fatigue behaviour of WAAM steel plates has therefore been undertaken and is reported herein. Following geometric, mechanical and microstructural characterisation, a series of WAAM coupons was tested under uniaxial high-cycle fatigue loading. A total of 75 fatigue tests on both as-built and machined coupons, covering various stress ranges and stress ratios (R = 0.1, 0.2, 0.3 and 0.4), have been conducted. The local stress concentrations in the as-built coupons induced by their surface undulations have also been studied by numerical simulations. The fatigue test results were analysed using constant life diagrams (CLDs) and S-N (stress-life) diagrams, based on both nominal and local stresses. The CLDs revealed that the fatigue strength of the as-built WAAM steel was relatively insensitive to the different stress ratios. The S-N diagrams showed that the surface undulations resulted in a reduction of about 35% in the fatigue endurance limit for the as-built WAAM material relative to the machined material, and a reduction of about 60% in fatigue life under the same load level. The as-built and machined WAAM coupons were shown to exhibit similar fatigue behaviour to conventional steel butt welds and S355 structural steel plates, respectively. Preliminary nominal stress-based and local stress-based S-N curves were also proposed for the WAAM steel

Signature Change in Noncommutative FRW Cosmology

The conditions for which the no boundary proposal may have a classical realization of a continuous change of signature, are investigated for a cosmological model described by FRW metric coupled with a self interacting scalar field, having a noncommutative phase space of dynamical variables. The model is then quantized and a good correspondence is shown between the classical and quantum cosmology indicating that the noncommutativity does not destruct the classical-quantum correspondence. It is also shown that the quantum cosmology supports a signature transition where the bare cosmological constant takes a vast continuous spectrum of negative values. The bounds of bare cosmological constant are limited by the values of noncommutative parameters. Moreover, it turns out that the physical parameters are constrained by the noncommutativity parametres.Comment: 15 pages, 4 figures, Minor revision, references adde

Resistance to acid attack, abrasion and leaching behavior of alkali-activated mine waste binders

This paper report results of a research project on the development of alkali-activated binders using mine wastes. Abrasion and acid resistance of two ordinary Portland cement (OPC) strength class concrete mixtures (C20/25 and C30/37) and several mine waste (MW) mixtures were compared. This study indicates that MW binders possess higher acid and abrasion resistance than OPC based concrete mixtures.The leaching assessment of the MW binders shows it can be considered an inert material which indicates that it could be used as a building material

Cement degradation in CO2 storage sites: a review on potential applications of nanomaterials

© 2018 The Author(s) Carbon capture and sequestration (CCS) has been employed to reduce global warming, which is one of the critical environmental issues gained the attention of scientific and industrial communities worldwide. Once implemented successfully, CCS can store at least 5 billion tons of CO2per year as an effective and technologically safe method. However, there have been a few issues raised in recent years, indicating the potential leakages paths created during and after injection. One of the major issues might be the chemical interaction of supercritical CO2with the cement, which may lead to the partial or total loss of the cement sheath. There have been many approaches presented to improve the physical and mechanical properties of the cement against CO2attack such as changing the water-to-cement ratio, employing pozzolanic materials, and considering non-Portland cements. However, a limited success has been reported to the application of these approaches once implemented in a real-field condition. To date, only a few studies reported the application of nanoparticles as sophisticated additives which can reinforce oil well cements. This paper provides a review on the possible application of nanomaterials in the cement industry where physical and mechanical characteristics of the cement can be modified to have a better resistance against corrosive environments such as CO2storage sites. The results obtained indicated that adding 0.5 wt% of Carbon NanoTubes (CNTs) and NanoGlass Flakes (NGFs) can reinforce the thermal stability and coating characteristics of the cement which are required to increase the chance of survival in a CO2sequestrated site. Nanosilica can also be a good choice and added to the cement by as much as 3.0 wt% to improve pozzolanic reactivity and thermal stability as per the reports of recent studies

Durability of Mortar Incorporating Ferronickel Slag Aggregate and Supplementary Cementitious Materials Subjected to Wet–Dry Cycles

This paper presents the strength and durability of cement mortars using 0–100% ferronickel slag (FNS) as replacement of natural sand and 30% fly ash or ground granulated blast furnace slag (GGBFS) as cement replacement. The maximum mortar compressive strength was achieved with 50% sand replacement by FNS. Durability was evaluated by the changes in compressive strength and mass of mortar specimens after 28 cycles of alternate wetting at 23 °C and drying at 110 °C. Strength loss increased by the increase of FNS content with marginal increases in the mass loss. Though a maximum strength loss of up to 26% was observed, the values were only 3–9% for 25–100% FNS contents in the mixtures containing 30% fly ash. The XRD data showed that the pozzolanic reaction of fly ash helped to reduce the strength loss caused by wet–dry cycles. Overall, the volume of permeable voids (VPV) and performance in wet–dry cycles for 50% FNS and 30% fly ash were better than those for 100% OPC and natural sand

A field demonstration project utilizing FRC/PCC residues for paving materials. Quarterly report, 1 December 1994--28 February 1995

In the past two years, Southern Illinois University at Carbondale (SIUC), under the sponsorship of Illinois Clean Coal Institute, has performed a series of laboratory research into engineering properties of roller compacted concretes containing fluidized bed combustion/pulverized coal combustion (FBC/PCC) by-products as well as FBC/PCC-portland cement concrete mixtures prepared under conventional placement technique. This laboratory effort has resulted in identification of a number of potentially viable commercial applications for the FBC by-products residues derived from Illinois high-sulfur coal. One potential and promising application of the FBC/PCC solid waste residues, which also accounts for the large utilization of coal-based by-product materials, is in pavement construction. The proposal presented herein is intended to embark into a new endeavor in order to bring the commercialization aspect of the initial laboratory project a step closer to reality by conducting a field demonstration of the optimized mixtures identified during the two -year laboratory investigation. A total of twenty-three different pavement slabs will be constructed at an identified site located in the Illinois Coal Development Park, Carterville, Illinois, by two construction contractors who are part of the industrial participants of the initial project and have expressed interest in the construction of experimental slabs. Both conventional and roller compacted concrete placement techniques will be utilized. All sections will be subjected to an extensive engineering evaluation and will be monitored for nearly a year for both short- and long-term performance. The field results will be compared to that of the equivalent laboratory-prepared mixes in order to ascertain the suitability of proposed mixes for field applications

A field demonstration project utilizing FBC/PCC residues for paving materials. Technical report, September 1--November 30, 1994

Research has been undertaken into engineering properties of roller compacted concretes containing fluidized bed combustion/pulverized coal combustion (FBC/PCC) by-products as well as FBC/PCC-Portland Cement concrete mixtures prepared using conventional placement technique. This laboratory effort has resulted in identification of a number of potentially viable commercial applications for the FBC by-products residues derived from Illinois high-sulfur coal. One potential and promising application of the FBC/PCC solid waste residues, which also accounts for the large utilization of coal-based by-product materials, is in pavement construction. The proposal presented herein is intended to embark into a new endeavor in order to bring the commercialization aspect of the initial laboratory project a step closer to reality by conducting a field demonstration of the optimized mixtures identified during the two-year laboratory investigation. A total of twenty-three different pavement slabs will be constructed at an identified site located in the Illinois Coal Development Park, Carterville, Illinois, by two construction contractors who are part of the industrial participants of the initial project and have expressed interest in the construction of experimental slabs. Both conventional and roller compacted concrete placement techniques will be utilized. All sections will be subjected to an extensive engineering evaluation and will be monitored for nearly a year for both short and long-term performance. The field results will be compared to that of the equivalent laboratory-prepared mixes in order to ascertain the suitability, of the proposed mixes for field application. During this reporting period, the physico-chemical and preconditioning characteristics of the raw materials were evaluated. Construction of the experimental road consisting of twenty-three surface and base course slab sections was also completed

A field demonstration project utilizing FBC/PCC residues for paving materials. Technical report, March 1--May 31, 1995

In the past two years, southern Illinois University at Carbondale (SIUC), under the sponsorship of Illinois Clean coal Institute, has performed a series of laboratory research into engineering properties of roller compacted concretes containing fluidized bed combustion/pulverized coal combustion (FBS/PCC) by-products as well as FBC/PCC-Portland cement concrete mixtures prepared under conventional placement technique. This laboratory effort has resulted in identification of a number of potentially viable commercial applications for the FBC by-products residues derived from Illinois high-sulfur coal. One potential and promising application of the FBC/PCC solid waste residues, which also accounts for the large utilization of coal-based by-product materials, is in pavement construction. A total of twenty-three different pavement slabs will be constructed at an identified site located in the Illinois Coal Development Park, Carterville, Illinois, by two construction contractors who are part of the industrial participants of the initial project. Both conventional and roller compacted concrete placement techniques will be utilized. All sections will be subjected to an extensive engineering evaluation and will be monitored for nearly a year for both short- and long-term performance. The field results will be compared to that of the equivalent laboratory- prepared mixes in order to ascertain the suitability of the proposed mixes for field applications. During this reporting period, the long- term durability of the field and laboratory vibratory-placed FBC/PCC surface and base concrete slabs were evaluated