Comparison of the identification performance of conventional FEM updating and integrated DIC

Full‐field identification methods are increasingly used to adequately identify constitutive parameters to describe the mechanical behavior of materials. This paper investigates the more recently introduced one‐step method of integrated digital image correlation (IDIC) with respect to the most commonly used two‐step method of finite element model updating (FEMU), which uses a subset‐based DIC algorithm. To make the comparison as objective as possible, both methods are implemented in the most equivalent manner and use the same FE model. Various virtual test cases are studied to assess the performance of both methods when subjected to different error sources: (1) systematic errors, (2) poor initial guesses for the constitutive parameters, (3) image noise, (4) constitutive model errors, and (5) experimental errors. Results show that, despite the mathematical similarity of both methods, IDIC produces less erroneous and more reliable results than FEMU, particularly for more challenging test cases exhibiting small displacements, complex kinematics, misalignment of the specimen, and image noise. Copyright © 2015 John Wiley & Sons, Ltd.     

A spectral‐element method for modelling cavitation in transient fluid–structure interaction

In an underwater‐shock environment, cavitation (boiling) occurs as a result of reflection of the shock wave from the free surface and/or wetted structure causing the pressure in the water to fall below its vapour pressure. If the explosion is sufficiently distant from the structure, the motion of the fluid surrounding the structure may be assumed small, which allows linearization of the governing fluid equations. In 1984, Felippa and DeRuntz developed the cavitating acoustic finite‐element (CAFE) method for modelling this phenomenon. While their approach is robust, it is too expensive for realistic 3D simulations. In the work reported here, the efficiency and flexibility of the CAFE approach has been substantially improved by: (i) separating the total field into equilibrium, incident, and scattered components, (ii) replacing the bilinear CAFE basis functions with high‐order Legendre‐polynomial basis functions, which produces a cavitating acoustic spectral element (CASE) formulation, (iii) employing a simple, non‐conformal coupling method for the structure and fluid finite‐element models, and (iv) introducing structure–fluid time‐step subcycling. Field separation provides flexibility, as it admits non‐acoustic incident fields that propagate without numerical dispersion. The use of CASE affords a significant reduction in the number of fluid degrees of freedom required to reach a given level of accuracy. The combined use of subcycling and non‐conformal coupling affords order‐of‐magnitude savings in computational effort. These benefits are illustrated with 1D and 3D canonical underwatershock problems. Copyright © 2004 John Wiley & Sons, Ltd.     

Identification of the continuum damage parameter: An experimental challenge in modeling damage evolution

To accurately predict ductile failures of new advanced metals, continuum damage models (CDMs) require experimental determination of material-specific damage parameter(s). While various experimental techniques are being used to determine these damage parameter(s), possible systematic errors due to methodological differences in damage definition have yet to be fully revealed. With the aim of finding the most reliable ductile damage quantification strategy for CDMs, this work provides an in-depth comparison of six theoretically equivalent methodologies by considering measurement accuracy, precision, damage spectrum, spatial resolution and practicality. It is found that the methodologies that quantify ductile damage from its geometry introduce significant systematic errors as they probe a very limited damage spectrum, whereas the methodologies that probe the degradation of a mechanical property suffer from low precision and high complexity, especially for high strains and material anisotropy.     

Impact of Grain Boundary Density on Oxide Scaling Revisited

Oxidation of Metals - A straightforward conceptual tool for discriminating between different oxide scaling processes deviating from the parabolic standard model is formulated. Grain boundary...     

Experimental analysis of the evolution of thermal shock damage using transit time measurement of ultrasonic waves

Thermal shock is a principal cause of catastrophic wear of the refractory lining of high temperature installations in metal making processes. To investigate thermal shock experimentally with realistic and reproducible heat transfer conditions, chamotte and corund refractory samples of ambient temperature were subjected to surface contact with molten aluminium followed by passive cooling in ambient air. The evolution of damage was characterized by measuring the transit time of ultrasonic longitudinal waves at various sample locations after each test cycle. The mechanical validity of transit time measurement was confirmed in independent experiments. The single test cycle performed with chamotte material indicated the reproducibility and reliability of the experimental set-up and damage characterization method. Multiple test cycles performed with corund material yielded a reliable set of data, to be used for model validation purposes. Both non-uniform damage due to temperature gradients as well as uniform damage due to exposure to a uniform temperature were determined experimentally. The interaction between both damage mechanisms requires further investigation as well as the possible shielding of heat transport by damage.     

A critical assessment of indentation-based ductile damage quantification

This paper scrutinizes the reliability of indentation-based damage quantification, frequently used by many industrial and academic researchers. In this methodology, damage evolution parameters for continuum damage models are experimentally measured by probing the deformation-induced degradation of either hardness or indentation modulus. In this critical assessment the damage evolution in different sheet metals was investigated using this indentation approach, whereby the obtained results were verified by other experimental techniques (scanning electron microscopy, X-ray microtomography and highly sensitive density measurements), and by finite element simulations. This extensive experimental–numerical assessment reveals that the damage-induced degradation of both hardness and modulus is at least partially, but most likely completely, masked by other deformation-induced microstructural mechanisms (e.g. grain shape change, strain hardening, texture development, residual stresses and indentation pile-up). It is therefore concluded that hardness-based or modulus-based damage quantification methods are intrinsically flawed and should not be used for the determination of a damage parameter.     

On the prediction of delamination during deep-drawing of polymer coated metal sheet

This paper describes the development and application of a numerical model that can predict the delamination of the polymer coating from the steel substrate during deep-drawing. Experimentally characterized cohesive zones are used to describe the interface between the polymer and the steel and are capable of modelling delamination or a prior partial loss of adhesion during an axisymmetric deep-drawing simulation. A parameter is proposed that quantifies the interfacial integrity and is used to assess the influence of the tooling radii, the clearance between the punch and the die and the coating thickness on the interfacial integrity.     

A multi-scale computational strategy for structured thin sheets

Engineering trends show an increasing use of multi-layered and structured thin sheets in innovative applications where the layer thickness approaches the microstructural scale. This paper presents a strategy to homogenize the actual three-dimensional heterogeneous sheet towards a shell continuum. Consistent scale transition relations are derived, providing the ability to solve the (generalized) stress-strain fields on both the microstructural and the engineering scale are obtained in a direct and coupled manner.     

Predictive FEM simulation of thermal shock damage in the refractory lining of steelmaking installations

Thermal shock damage in the refractory lining of steelmaking installations is modelled using an experimentally validated constitutive damage framework which is coupled incrementally with a thermo-elastic FE package. Both non-local elasticity-based damage induced by temperature gradients and thermal damage induced by a uniform temperature increase contribute to the total damage. The non-locality is spatially discretized using a Galerkin approach within a finite element context. The thermal shock damage in a snorkel of a steel degassing installation as well as in the refractory lining of a steel ladle is modelled to demonstrate the applicability of the computational platform.     

The prevalence of PSE characteristics in pork and cooked ham — Effects of season and lairage time

A total of 180 pigs was slaughtered in the same slaughterhouse, but divided in six different trials distributed over Winter (December–March) and Summer (April–September). Meat quality measurements (pH, electrical conductivity, color and/or water-holding capacity) were carried out 30 min, 24 and/or 35 h after slaughter in three different muscles: M. gracilis, M. semimembranosus and M. longissimus dorsi. A tendency towards a higher proportion of PSE meat during Summer was found in the examined muscles. Moreover a higher protein, higher dry matter content, a lower water/protein ratio and a lower slicing yield were found for the cooked hams suggesting a higher PSE prevalence in the Summer. A lairage time between 2 and 4 h during Summer and less than 2 h during Winter was related to a lower proportion of PSE meat. The correlation coefficients between the individual meat quality variables were moderate, but showed the predictive power of the pH measured 24 h post-mortem in the M. gracilis for meat quality.