The Journal of Strain Analysis for Engineering Design

Innovative designs of transport vehicles need to be validated in order to demonstrate reliability and provide confidence. It is normal practice to study the mechanical response of the structural elements by comparing numerical results obtained from finite element simulation models with results obtained from experiment. In this frame, the use of whole-field optical techniques has been proven successful in the validation of deformation, strain, or vibration modes. The strength of full-field optical techniques is that the entire displacement field can be acquired. The objective of this article is to integrate full-field optical measurement methodologies with state-of-the-art computational simulation techniques for nonlinear transient dynamic events. In this frame, composite car bonnet frame structures of dimensions about 1.8 m × 0.8 m are considered. They have been tested in low-velocity mass-drop impact loading with impact energies ranging from 20 to 200 J. In parallel, simulation models of the car bonnet frame have been developed using layered shell elements. The Zernike shape descriptor approach was used to decompose numerical and experimental data into moments for comparison purposes. A very good agreement between numerical and experimental results was observed. Therefore, integration of numerical analysis with full-field optical measurements along with sophisticated comparison techniques can increase design reliability.

Recent advances in measurement techniques such as digital image correlation, automated photoelasticity, electronic speckle pattern interferometry and thermoelastic stress analysis allow full-field maps (images) of displacement or strain to be obtained easily. This generally results in the acquisition of large volumes of highly redundant data. Fortunately, image decomposition offers feasible techniques for data condensation while retaining essential information. This permits data processing such as the validation of computational models, modal testing or structural damage assessment efficiently and in a straightforward way. The selection, or construction, of decomposition bases (kernel) functions is essential to data reduction and has been shown to produce features, or attributes, of the full-field image that are effective in reproducing the measured information, succinct in condensation and robust to measurement noise. Among the most popular kernel functions are the orthogonal Fourier series, wavelets and Legendre polynomials, which are defined on continuous rectangular domains, and Zernike polynomials and Fourier–Mellin functions, which are defined on continuous circular domains. The discrete orthogonal polynomials include Tchebichef, Krawtchouk and Hahn functions that are directly applicable to digital images and avoid the approximate numerical integration that becomes necessary with the sampling of continuous kernel functions. In practice, full-field measurements of the engineering components are usually non-planar within irregular domains – neither rectangular nor circular, so that the classical kernel functions are not immediately applicable. To address this problem, a complete methodology is described, consisting of (1) surface parameterisation for the mapping of three-dimensional surfaces to two-dimensional planar domains, (2) Gram–Schmidt orthogonalisation for the construction of orthogonal kernel functions on arbitrary domains and (3) reconstruction of localised image features, such as regions of high strain gradient, by a windowing technique. Application of this methodology is demonstrated in a series of illustrative examples

The need to provide strong evidence of the validity of predictions from computational solid mechanics models used in engineering design decisions is discussed. A new procedure is proposed, based on image decomposition, for reducing the dimensionality of strain field data from models and experiments and then comparing the resultant feature vectors via a simple linear correlation in which validation is deemed to be achieved when the coordinate pairs from the two feature vectors lie within a scatter band defined by the minimum measurement uncertainty. The procedure is illustrated by some simple examples that allow the advantages and drawbacks of the approach to be highlighted. It is anticipated that the procedure could become part of a corporate plan or regulatory process for verification and validation of computational solid mechanics models.

Experimental strain analysis, structural health monitoring and non-destructive testing and evaluation are regarded as separate disciplines that, in general, are deployed independently at different phases in the life cycle of an engineering component, i.e. in the design process, in service and after an event or service period, respectively. It is proposed that the integrated use of these three disciplines is advantageous and beneficial in terms of reduced capital and operational costs for critical and safety-relevant components, as well as, in validating simulations, in both quantifying and reducing risk of unexpected failure, and in estimating remanent life. We propose the foundation of this integration to be data-rich strain fields measured and compared quantitatively, with each other and with data from simulations, at temporal intervals during the life of a component.

The purpose of this article is to investigate the so-called verification and validation methodology for the vibration study of automotive structures, in particular natural frequencies and frequency response functions. In computational mechanics, the main objective of verification and validation leading to numerical and experimental works is to assess and improve the predictive capability of finite element models. Three main applications are presented throughout the article. The first application deals with spot weld modelling techniques. Four spot weld models are critically investigated for this study, namely two point-to-point and two surface-to-surface approaches. Two examples are treated: an assembly of two plates with three spot welds and a cradle. The second application deals with modelling galvanized structures. The study is focussed on automotive engine cradles. Experimental comparison between welded and galvanized assemblies highlights the mechanical effects due to galvanization. Finite element models, specifically developed for galvanized assemblies, are presented. The third application deals with a vehicle windscreen that is a sandwich structure made of glass and polymers. The dynamic behaviour of the windscreen under free–free conditions, in the presence of intra variability due to temperature variation, is discussed. Solid finite element models and multilayer shell models are assessed and compared.