Fracture Response of Metallic Particulate-reinforced Cementitious Composites: Insights from Experiments and Multiscale Numerical Simulations

This paper presents an experimental and numerical investigation into the fracture response of mortars containing up to 30% waste iron powder by volume as OPC-replacement. The iron powder-modified mortars demonstrate significantly improved strength and fracture properties as compared to the control mortars due to presence of elongated iron particulates in the powder. With a view to develop a predictive tool towards materials design of such particulate-reinforced systems, fracture responses of iron powder-modified mortars are simulated using a multiscale numerical approach. The approach implements multi-scale numerical homogenization involving cohesive zone-based damage at the matrix-inclusion interface and isotropic damage in the matrix to obtain composite constitutive response and fracture energy. Consequently, these results serve as input to macro-scale XFEM-based three-point-bend simulations of notched mortar beams. The simulated macroscopic fracture behavior exhibit excellent match with the experimental results. Thus, the numerical approach links the material microstructure to macroscopic fracture parameters facilitating microstructure-guided material design

Microstructure-guided numerical simulation to evaluate the influence of phase change materials (PCMs) on the freeze-thaw response of concrete pavements

The use of phase change materials in infrastructure has gained significant attention in the recent years owing to their robust thermal performance. This study implements a numerical simulation framework using finite element analysis to evaluate the influence of phase change materials (PCMs) on the thermal response of concrete pavements in geographical regions with significant winter weather conditions. The analysis is carried out at different length scales. The latent-heat associated with different PCMs is efficiently incorporated into the simulation framework. Besides, the numerical simulation framework employs continuum damage mechanics to evaluate the influence of PCMs on the freeze-thaw induced damage in concretes. The simulations show significant reductions in the freeze-thaw induced damage when PCMs are incorporated in concrete. The numerical simulation framework, developed here, provides efficient means of optimizing the material design of such durable PCM-incorporated concretes for pavements by tailoring the composition and material microstructure to maximize performance

A Peridynamics-Based Micromechanical Modeling Approach for Random Heterogeneous Structural Materials

This paper presents a peridynamics-based micromechanical analysis framework that can efficiently handle material failure for random heterogeneous structural materials. In contrast to conventional continuum-based approaches, this method can handle discontinuities such as fracture without requiring supplemental mathematical relations. The framework presented here generates representative unit cells based on microstructural information on the material and assigns distinct material behavior to the constituent phases in the random heterogenous microstructures. The framework incorporates spontaneous failure initiation/propagation based on the critical stretch criterion in peridynamics and predicts effective constitutive response of the material. The current framework is applied to a metallic particulate-reinforced cementitious composite. The simulated mechanical responses show excellent match with experimental observations signifying efficacy of the peridynamics-based micromechanical framework for heterogenous composites. Thus, the multiscale peridynamics-based framework can efficiently facilitate microstructure guided material design for a large class of inclusion-modified random heterogenous materials

Fracture Toughness of Fly Ash-Based Geopolymer Gels: Evaluations Using Nanoindentation Experiment and Molecular Dynamics Simulation

This paper presents the fracture toughness of sodium aluminosilicate hydrate (N-A-S-H) gel formed through alkaline activation of fly ash. While the fracture toughness of N-A-S-H is obtained experimentally from nanoindentation experiment implementing the principle of conservation of energy, the numerical investigation is performed via reactive force field molecular dynamics. A statistically significant number of indentations are performed on geopolymer paste yielding frequency distribution of Young’s modulus. Four distinct peaks are observed in the frequency distribution plot from which the peak corresponding to N-A-S-H was separated using statistical deconvolution technique. The young’s modulus of N-A-S-H, thus obtained from statistical deconvolution shows excellent match with the values reported in the literature, thus confirming successful identification of indentations corresponding to N-A-S-H. From the load-penetration depth responses of N-A-S-H, fracture toughness was obtained following the principle of conservation of energy. The experimental fracture toughness shows good correlation with the simulated fracture toughness of N-A-S-H, obtained from reactive force field molecular dynamics. The fracture toughness of N-A-S-H presented in this paper paves the way for multiscale simulation-based design of tougher geopolymer binders

Fracture Toughness of Fly Ash-Based Geopolymer Gels: Evaluations Using Nanoindentation Experiment and Molecular Dynamics Simulation

This paper presents the fracture toughness of sodium aluminosilicate hydrate (N-A-S-H) gel formed through alkaline activation of fly ash. While the fracture toughness of N-A-S-H is obtained experimentally from nanoindentation experiment implementing the principle of conservation of energy, the numerical investigation is performed via reactive force field molecular dynamics. A statistically significant number of indentations are performed on geopolymer paste yielding frequency distribution of Young’s modulus. Four distinct peaks are observed in the frequency distribution plot from which the peak corresponding to N-A-S-H was separated using statistical deconvolution technique. The young’s modulus of N-A-S-H, thus obtained from statistical deconvolution shows excellent match with the values reported in the literature, thus confirming successful identification of indentations corresponding to N-A-S-H. From the load-penetration depth responses of N-A-S-H, fracture toughness was obtained following the principle of conservation of energy. The experimental fracture toughness shows good correlation with the simulated fracture toughness of N-A-S-H, obtained from reactive force field molecular dynamics. The fracture toughness of N-A-S-H presented in this paper paves the way for multiscale simulation-based design of tougher geopolymer binders

Record of stranded whales along Karnataka coast

A whale was stranded in the beach of Guijerbettu, Udupi district, Karnataka on 21.12.2001 . The whale was found in live condition. Thelocal person tried to rescue it but was in vain and later it died. The whale was identified as Balaenopteramusculus (Blue whale). Few vertebrae have been collected and preserved in the museum of Mangalore Research Centre of CMFRI for future identification up to the species level. Another whale (genus : Balaenoptera) was stranded in Kota, Udupi district, Karnataka near the shore of Arama temple on 11.08.2004 in decayed condition

Fracture toughness of sodium aluminosilicate hydrate (NASH) gels: Insights from molecular dynamics simulations

This paper evaluates the fracture toughness of sodium aluminosilicate hydrate (N-A-S-H) gel formed through alkaline activation of fly ash via molecular dynamics (MD) simulations. The short- and medium-range order of the constructed N-A-S-H structures shows good correlation with the experimental observations, signifying the viability of the N-A-S-H structures. The simulated fracture toughness values of N-A-S-H (0.4–0.45 MPa m0.5) appear to be of the same order as the available experimental values for fly ash-based geopolymer mortars and concretes. These results suggest the efficacy of the MD simulation toward obtaining a realistic fracture toughness of N-A-S-H, which is otherwise very challenging to obtain experimentally, and no direct experimental fracture toughness values are yet available. To further assess the fracture behavior of N-A-S-H, the number of chemical bonds formed/broken during elongation and their relative sensitivity to crack growth are evaluated. Overall, the fracture toughness of N-A-S-H presented in this paper paves the way for a multiscale simulation-based design of tougher geopolymers

Dynamic compressive behavior of metallic particulate-reinforced cementitious composites: SHPB experiments and numerical simulations

An experimental and numerical evaluation on the dynamic compressive response of mortars containing up to 20% waste iron powder as sand replacement is presented in this paper. The dynamic response is evaluated using split Hopkinson pressure bar (SHPB) apparatus under high strain rates (up to 250/s). The elongated iron particulates present in the iron powder-incorporated mortars warrant significantly improved compressive strength and energy absorption capacity at high strain rates. Multiscale numerical simulations are performed with a view to develop a tool that facilitates microstructure-guided design of these particulate-reinforced mortars for efficient dynamic performance. The dynamic compressive response of particulate-reinforced mortars is simulated adopting a numerical approach that incorporates strain rate-dependent damage in a continuum micromechanics framework. The simulated dynamic compressive strengths and energy absorption capacities for mortars with various iron powder content exhibit good correlation with the experimental observations thereby validating the efficacy of the simulation approach

Mechanisms of barrier layer formation and erosion from in situ observations in the Bay of Bengal

During the Bay of Bengal (BoB) Boundary Layer Experiment (BoBBLE) in the southern BoB, time series of microstructure measurements were obtained at 8N, 89E from 4-14 July, 2016. These observations captured events of barrier layer (BL) erosion and re-formation. Initially, a three-layer structure was observed: a fresh surface mixed layer (ML) of thickness 10-20 m; a BL below of 30-40 m thickness with similar temperature but higher salinity; a high salinity core layer, associated with Summer Monsoon Current. Each of these three layers was in relative motion to the others, leading to regions of high shear at the interfaces. However, haline stratification overcame the destabilising influence of the shear regions, and preserved the three-layer structure. A salinity budget using in situ observations suggested that during the BL erosioni, high salinity surface waters (34.5 PSU) with weak stratification were advected to the time series location and replaced the three-layer structure with a deep ML (~60 m). Weakened stratification at the time series location also allowed atmospheric wind forcing to penetrate deeper. Turbulent kinetic energy dissipation rate and eddy diffusivity showed elevated values above 10-7 W kg-1 and 10-4 m2 s-1, respectively, in the upper 60 m. Later, the surface salinity decreased again (33.8 PSU) through horizontal advection, stratification became stronger and elevated mixing rates were confined to the upper 20 m, and the BL reformed. A 1-D model analysis suggests that in the study region, advection of temperature-salinity characteristics is essential for the maintenance of the BL and to the extent to which mixing penetrates the water column

Ethnicity and the professional socialisation of teachers: final report to the Teacher Training Agency

This report draws together the outcomes of a programme of research that has extended over two years. The project, which was financed by the Teacher Training Agency (TTA), aimed to fill some important gaps in our understanding of issues surrounding the recruitment of people from ethnic minorities into the teaching profession, and their subsequent experiences during training and in their first appointments. The project was organised under five interlocking strands. The first consisted of a postal questionnaire to all 1998 Postgraduate Certificate in Education (PGCE) entrants who had identified themselves in the Graduate Teacher Training Registry’s (GTTR) returns as being from an ethnic minority, or who had ticked the category of ‘Other’. The questionnaire invited the respondents to comment on a range of issues concerning their motivations for entering teaching and for choosing the particular institution in which they were to train. Two hundred and eighty-nine of the 776 questionnaires sent out were returned, giving a satisfactory response rate for this kind of survey. The second strand examined a similar set of issues from the perspectives of PGCE staff in sixteen initial teacher training institutions, with above average ethnic minority intakes. This strand, which was based on interviews with course directors, admissions tutors and other key personnel, was conducted in seven pre-1992 universities, eight post-1992 universities and one SCITT (i.e. an institution providing school-centred initial teacher training). In the third strand of the study, we returned to many of the same institutions and, with their help, set up interviews with a cross-section of respondents to the trainee questionnaire. In all, forty-nine trainees participated. The fourth strand involved another questionnaire, this time going to newly qualified teachers (NQTs) who had just completed a PGCE course (i.e. the same cohort as had been targeted in the first strand). The main NQT sample comprised 149 respondents. Finally, in the fifth strand, we followed up forty-four of the respondents from the main NQT sample to obtain their personal reflections after nearly one year of teaching. As well as giving a detailed account of each strand of the research, the report also provides a critical bibliography of related work from recent years, an account of the methodologies used, and a set of conclusions and recommendations. The methodology section highlights the limitations of a study such as this, and should be read carefully before any claims are made on the basis of our work. This executive summary draws attention to the main points in each part of the report. 5 On 1 September 2005 the Teacher Training Agency (TTA) became the Training and Development Agency for Schools (TDA) and took on an expanded remit. Visit www.tda.gov.uk for further information. We are re-branding our literature only when necessary