SIM University Singapore

Singapore, Singapore

SIM University Singapore

Singapore, Singapore
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Lim T.-C.,SIM University Singapore
Materials Science Forum | Year: 2016

This paper addresses the problem of the speed of plane waves of dilatation, in which the impacted end is sustained so as to maintain constant strain behind the wave front, through auxetic solids considering density correction; the importance of this work can be inferred from the lack of knowledge on this type of material. Results for the dimensionless wave speed reveal that the Poisson’s ratio magnitude and the strain play primary and secondary roles, respectively. In addition, there is better control of wave speed in the auxetic region than in the conventional region due to a more gradual change of the wave speed in the former. Hence the use of auxetic materials facilitates better passive control of wave propagation in bulk solids. © 2016 Trans Tech Publications, Switzerland.


Ng W.,SIM University Singapore | Diener E.,University of Illinois at Urbana - Champaign
Journal of Personality and Social Psychology | Year: 2014

This study explored the importance of financial satisfaction versus postmaterialist needs for subjective well-being (SWB). Using the Gallup World Poll, we examined whether financial satisfaction and postmaterialist needs (pertaining to autonomy, social support, and respect) were universal predictors of the different components of SWB across the world, and whether their effects were moderated by national affluence. Results showed that financial satisfaction was the strongest predictor of life evaluation, whereas respect was the strongest predictor of positive feelings. Both measures predicted negative feelings to some extent. Multilevel analyses also revealed moderating effects of societal wealth. The association between financial satisfaction and SWB and that between postmaterialist needs and SWB were stronger in richer nations compared with poorer ones. This suggests that developed economies should continue to focus on both material and psychological aspects, and not disregard economic gains, as both measures are essential to well-being. © 2014 American Psychological Association.


Lim T.-C.,SIM University Singapore
Smart Materials and Structures | Year: 2013

This paper aims to understand the effect of auxeticity on shear deformation in thick plates. Three models for the shear correction factor of plates as a function of Poisson's ratio were proposed: an analytical model, a cubic fit model and a modified model. Of these three, the cubic fit model exhibits the best accuracy over the entire range of Poisson's ratio from -1 to 0.5. The extent of shear deformation is herein investigated using the example of uniformly loaded circular plates. It was found that the maximum deformation of such plates based on Mindlin theory approximates to those according to Kirchhoff theory when the Poisson's ratio of the plate material is highly negative. When the Poisson's ratio of the plate material is -1 and the edge of the plate is simply supported, the calculation of the maximum deflection by Mindlin theory simplifies into that by Kirchhoff theory. These results suggest that auxeticity reduces shear deformation in thick plates, permitting the use of classical plate theory for thick plates only if the plate material is highly auxetic. © 2013 IOP Publishing Ltd.


Lim T.-C.,SIM University Singapore
Smart Materials and Structures | Year: 2013

This paper establishes the effect of auxeticity on stress wave transmission and reflection. Specifically, investigation was made on wave transmission across two perfectly bonded isotropic solids in which the Poisson's ratios ranged between -1 and 0.5. The results show that the combined use of auxetic and conventional solids at extreme Poisson's ratio is helpful to multiply or even to eliminate stress waves, under the prescribed density and modulus relations. These results suggest the usefulness of auxetic solids as smart materials and in smart structures for effective control of stress wave transmission. © 2013 IOP Publishing Ltd.


Lim T.-C.,SIM University Singapore
Smart Materials and Structures | Year: 2014

Auxetic materials and structures exhibit a negative Poisson's ratio while thick plates encounter shear deformation, which is not accounted for in classical plate theory. This paper investigates the effect of a negative Poisson's ratio on thick plates that are subjected to buckling loads, taking into consideration the shear deformation using Mindlin plate theory. Using a highly accurate shear correction factor that allows for the effect of Poisson's ratio, the elastic stability of circular and square plates are evaluated in terms of dimensionless parameters, namely the Mindlin-to-Kirchhoff critical buckling load ratio and Mindlin critical buckling load factors. Results for thick square plates reveal that both parameters increase as the Poisson's ratio becomes more negative. In the case of thick circular plates, the Mindlin-to-Kirchhoff critical buckling load ratios and the Mindlin critical buckling load factors increase and decrease, respectively, as the Poisson's ratio becomes more negative. The results obtained herein show that thick auxetic plates behave as thin conventional plates, and therefore suggest that the classical plate theory can be used to evaluate the elastic stability of thick plates if the Poisson's ratio of the plate material is sufficiently negative. The results also suggest that materials with highly negative Poisson's ratios are recommended for square plates, but not circular plates, that are subjected to buckling loads. © 2014 IOP Publishing Ltd.


Lim T.C.,SIM University Singapore
Applied Mechanics and Materials | Year: 2013

Auxetic materials are solids that possess negative Poisson's ratio. Although rare, such materials do occur naturally and also have been artificially produced. Due to their unique properties, auxetic materials have been extensively investigated for load bearing applications including in biomedical engineering and aircraft structures. This paper considers the effect of Poisson's ratio on the stress concentration factors on rods with hyperbolic groove and large thin plates with circular holes and rigid inclusions. Results reveal that the use of auxetic materials is useful for reducing stress concentration in the maximum circumferential stress of the rods with grooves, and in plates with circular holes and rigid inclusions. However, the use of auxetic materials increases the stress concentration in the axial direction of the rod. Therefore a procedure to accurately select and/or design materials with precise negative Poisson's ratio for optimal design is suggested for future work. © (2013) Trans Tech Publications, Switzerland.


Lim T.-C.,SIM University Singapore
International Journal of Applied Mechanics | Year: 2014

The influence of auxeticity on the mechanical behavior of isotropic plates is considered herein by evaluating the plate flexural rigidity as the Poisson's ratio changes from 0.5 to -1. Since the change in plate's Poisson's ratio is followed by a change in at least one of the three moduli, any resulting change to the plate flexural rigidity is only meaningful when at least one of the moduli is held constant. This was performed by normalizing the plate flexural rigidity by a single modulus, a square root of two moduli product, or a cube root of three moduli product to give a dimensionless plate flexural rigidity. It was found that the plate flexural rigidity decreases to a minimum as the plate Poisson's ratio decreases from 0.5 to 0 when only the Young's modulus is held constant. Thereafter the plate flexural rigidity increases with the plate auxeticity. Results also reveal that when only the shear modulus or when the bulk modulus is held constant, the plate flexural rigidity decreases or increases, respectively, with the plate auxeticity. Intermediate trend in the plate flexural rigidity is observed when the product of two moduli is held constant. When the product of all three moduli is held constant, the plate flexural rigidity increases with the plate auxeticity, and the change is especially drastic when the plate Poisson's ratio is near to the upper and lower limits of Poisson's ratio for isotropic solids. Results from this work are useful for structural designers to control the flexural rigidity of plate made from auxetic materials. © 2014 Imperial College Press.


Chan C.M.L.,SIM University Singapore
Proceedings of the Annual Hawaii International Conference on System Sciences | Year: 2013

Noting the need to extend the corpus of knowledge on open government data initiatives, especially on the strategies to facilitate and attract businesses and citizens to participate, collaborate and re-use open government data, this paper presents a research-in-progress case study on an open data initiative by the Singapore Government. Preliminary findings indicate that open innovation can be gainfully employed to realize the underlying motivation of open data initiatives. This research also builds upon existing study in open innovation strategies. It posits a set of considerations to develop the open government data portal into an open innovation platform. It also establishes a set of considerations for enticing businesses and citizens to create e-services that leverage on the datasets available from the portal. Implications to both research and practice of open government data initiatives are presented. The paper concludes with a discussion on the future research direction of this study. © 2012 IEEE.


Lim T.-C.,SIM University Singapore
Physica Status Solidi (B) Basic Research | Year: 2014

A variant of the auxetic helical yarn is explored herein by means of sewing an inextensible thin cord through an elastic fat cord, in a triangular pattern, to form a semi-auxetic yarn. When stretched in the longitudinal direction, the semi-auxetic yarn exhibits conventional and auxetic behavior in the plane perpendicular and parallel, respectively, to the plane which the inextensible thin cord lies on. A simplified model is developed herein to describe the effective Poisson's ratio of the yarn in the conventional and auxetic planes in terms of the initial half angle of the thin cord and the Poisson's ratio of the fat cord. Results show that the Poisson's ratio of the yarn in the auxetic plane decreases and increases with the initial half angle of the thin cord and the Poisson's ratio of the fat cord, respectively, while the Poisson's ratio of the yarn in the conventional plane increases with both parameters. In addition, the dominant parameters for the yarn in the auxetic and conventional planes are the initial half angle of the thin cord and the Poisson's ratio of the fat cord, respectively. Finally, other types of semi-auxetic yarns in the same category are proposed with suggested ways of producing them. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Lim T.-C.,SIM University Singapore
Physica Status Solidi (B) Basic Research | Year: 2012

Previously, a sandwich structure in which the Poisson ratios of the core and facesheets possess opposite signs has been shown to exhibit overall conventional and auxetic behavior depending on the loading mode - axial loading or bending - for an intermediate range of relative core thickness. In addition to these two loading modes, sandwich structures in aerospace applications encounter torsional loads. In this paper, the effective Poisson's ratio for torsional loading is proposed. Results show that, depending on the loading mode and the relative core thickness, there can be up to four levels of overall auxeticity, namely (i) full auxeticity (FA) if the structure behaves as an auxetic structure under all three modes of loading, (ii) high auxeticity (HA) if the structure behaves as an auxetic structure in two of the loading modes, (iii) low auxeticity (LA) if the structure behaves as an auxetic structure in only one of the loading modes, and (iv) no auxeticity (NA) if the structure behaves as a conventional structure under all of the three loading modes. These results indicate that by selecting the Poisson's ratios and the thickness of the cores and facesheets, the sandwich structure can be made to respond differently under different external loading conditions. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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