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a b s t r a c tFinite element model updating is an inverse problem based on measured structural outputs, in this case maximum principal strain measured using digital image correlation. Full-field responses in the form of strain maps contain valuable information for model updating but within large volumes of highly-redundant data. In this paper, shape descriptors based on Zernike polynomials having the properties of orthogonality and rotational invariance are shown to be powerful decomposition kernels for defining the shape or map of the strain distribution. A square plate with a circular hole subject to a uniaxial tensile load is considered and effective shape features are constructed using a set of modified Zernike polynomials. The modification includes the application of a decaying weighting function to the Zernike polynomials so that high strain magnitudes around the hole are well-represented. The Gram-Schmidt process is then used to ensure orthogonality for the obtained decomposition kernels over the domain of the specimen, i.e. excluding the hole. Results show that only a very small number of Zernike moment descriptors are necessary and sufficient to represent the full-field data. The onset of yielding may be quantified using the descriptors. Furthermore, model updating of nonlinear elasto-plastic material properties is carried out using the Zernike moment descriptors derived from full-field strain measurements.

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Auxetic materials have a negative Poisson's ratio, which can enhance other properties. Greater indentation resistance and energy absorption, as well as synclastic curvature, could lend auxetic materials well to protective sports equipment and clothing. Sheets of foam often form padding within protective equipment, but producing large homogenous auxetic foam samples is challenging. The aim of this work was to investigate techniques to fabricate large thin sheets of auxetic foam, to facilitate future production and testing of prototype sports equipment utilizing this material. A mold was developed to fabricate sheets of auxetic foam − with planar dimensions measuring 350 × 350 mm − using the thermo‐mechanical process. The mold utilized through‐thickness rods to control lateral compression of foam. Sheets of auxetic foam measuring 10 × 350 × 350 mmd were fabricated and characterized. Each sheet was cut into nine segments, with density measurements used to determine how evenly the foam had been compressed during fabrication. Specimens cut from corner and centre segments were subject to quasi‐static extension up to 30% to obtain stress versus strain relationships, with Digital Image Correlation used to determine Poisson's ratio. Specimens cut from the corner tended to have a marginally higher density, lower stiffness and more consistent negative Poisson's ratio compared to those from the centre, indicating some inconsistency in the conversion process. Future work could look to improve fabrication techniques for large thin homogenous sheets of auxetic foam.

This paper investigates the effects of rural households’ demographic characteristics on formal credit constraint, and explores the relationship between informal and formal lending in rural China. Using 2013 China’s Household Finance survey data, the authors apply probit regression models to investigate the effects of demographic factors on formal credit constraint and the household’s decision to borrow from informal credit sources. In addition, the endogenous switching regression model is applied to evaluate the impact of credit constraint on the welfare of rural farm households. The empirical evidence confirms that age, family size, annual household nonagricultural income, level of education, and history of informal borrowing have significant influence over credit constraint. Moreover, annual household nonagricultural income, the presence of children, borrowing from social networks and monthly communication expenses significantly impact rural households’ decision to utilise informal borrowing. Results from the endogenous switching regression model suggest that credit constraint by formal credit sources has no impact on household consumption.

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