Identification of Young's Modulus from Indentation Testing and Inverse Analysis

International audienceIn this study, a numerical method for the identification of the Young's modulus of linear elastic coated materials from continuous indentation test is first presented. The identification is based on an inverse analysis where the minimization of a cost functional is performed by a gradient descent algorithm. The main result is the computation of cost function gradient by using a direct differentiation technique, resulting in a time saving method compared to the widely used finite difference method. The validity and illustration of this approach is shown through several numerical examples. The second part of this article is dedicated to the identification of elasto-plastic thin films Young's modulus. A new method is proposed, where the inverse analysis relies only on finite element computations for elastic materials

Inverse Analysis of Multiple Indentation Unloading Curves for Thin Film Young's Modulus Evaluation

International audienceThe Oliver and Pharr method is the prevailing process for thin films Young's modulus evaluation. Introduced initially for homogeneous materials, this method does not account for the substrate and can consequently lead to significant error, especially at large indentation depths. We suggest here possible methods to improve the accuracy by making use of inverse analysis and finite element computations of the one layer elastic indentation problem

Recombinant human interleukin 6 (B-cell stimulatory factor 2) is a potent inducer of differentiation of mouse myeloid leukemia cells (M1)

AbstractRecombinant human interleukin 6 (IL-6), a lymphokine involved in the final differentiation of activated B-cells into antibody-forming cells, greatly suppressed proliferation and induced differentiation of murine myeloid leukemia cells (M1) into mature macrophage-like cells. When M1 cells were treated with IL-6, their growth was completely arrested as early as on day 2, and they were induced to differentiate morphologically into macrophage-like cells. Differentiation-associated properties such as phagocytic activity, adherence to the dish surface, Fc and C3 receptors, were also induced within 24 h by IL-6, and they reached their respective maximal levels on day 2 or 3. The potency of IL-6 in suppressing proliferation and inducing differentiation was much greater than that of 1α,25-dihydroxyvitamin D3 one of the most potent inducers of M1 cells. The present report indicates that IL-6 is involved in the differentiation of not only B-cells but also myeloid leukemia cells

Scaling effect on the detachment of pressure-sensitive adhesives through fibrillation characterized by a probe-tack test

This study extensively investigates the fibrillation process of a pressure-sensitive adhesive (PSA) using a probe-tack test. It was conducted using a glass sphere at the millimeter scale for various thicknesses of PSA layers laminated on a glass substrate, on various contact areas. A sharp decrease in the adhesion force caused by cavity growth was confirmed in the case of large contact areas, whereas cavities were not generated in the case of small contact areas on the thick PSA layer. Furthermore, an atomic force microscopy (AFM) cantilever was used to conduct a probe-tack test on considerably smaller contact areas at the micrometer scale, to focus on the fibrillation process by avoiding the cavity-growth. The transition of the adhesion force during the release process by the AFM cantilever was confirmed to resemble the transition in the fibrillation process obtained using the glass sphere by the repeated tests using the probe without cleaning the surface. The fully adhesive failure was also confirmed by the tests at sufficiently high release velocity. A comparison of these tests at different scales revealed that the detachment force from the probe at the millimeter scale is proportional to the contact area, and determined using the release-strain rate through elongation of the entire thickness of the PSA layer. By contrast, the detachment force from the AFM cantilever is proportional to the contact radius and determined using the release velocity regardless of the PSA thickness

FRACTURE BEHAVIOR OF ACRYLONITRILE-BUTADIENE-STYRENE RESIN

In this research, mixed mode loading testing of actylonitrile-butadiene-styrene (ABS) resin was carried out by using a compact tension shear specimen which was attached to a special loading device. The angle between the loading axis and the crack surface was varied from 90o (Mode I) to 0° (Mode I1). Two types of ABS resin were examined. The ï¬rst one (ABS-I) has a butadiene rubber content of 18 wt % in the form of small particles of diameter about 200 nm. The second one (ABS-2) has the same overall butadiene rubber content but a bimodal particle distribution with diameters of 200 nm and 500 nm. Crack initiation and propagation was observed by using a video microscope. The results show that the fracture angle for both materials under mixed mode loading coincides with the values predicted by the maximum hoop stress criterion. To obtain the stress intensity flzctors, numerical analyses of compact-tension-shear specimen were conducted using a two dimensional ï¬nite element analysis. Fracture behavior of ABS resins under mixed mode loading was almost the same as that under mode I loading for lower value of mode 11 component. However, for higher mode II component, shear type fracture occurred at initial crack tip

Transient Dynamic Response of Delaminated Composite Rotating Shallow Shells Subjected to Impact

In this paper a transient dynamic finite element analysis is presented to study the response of delaminated composite pretwisted rotating shallow shells subjected to low velocity normal impact. Lagrange's equation of motion is used to derive the dynamic equilibrium equation and moderate rotational speeds are considered wherein the Coriolis effect is negligible. An eight noded isoparametric plate bending element is employed in the finite element formulation incorporating rotary inertia and effects of transverse shear deformation based on Mindlin's theory. To satisfy the compatibility of deformation and equilibrium of resultant forces and moments at the delamination crack front a multipoint constraint algorithm is incorporated which leads to unsymmetric stiffness matrices. The modified Hertzian contact law which accounts for permanent indentation is utilized to compute the contact force, and the time dependent equations are solved by Newmark's time integration algorithm. Parametric studies are performed in respect of location of delamination, angle of twist and rotational speed for centrally impacted graphite-epoxy composite cylindrical shells

Evaluation of interfacial strength between fiber and matrix based on cohesive zone modeling

This paper presents a measurement technique of interfacial strength considering non-rigid bonding on a fiber/matrix interface modeled as a cohesive surface. By focusing on the stress concentration near a fiber crack obtained from a single-fiber fragmentation test, the stress contours in matrix observed by photoelasticity can be related to the interfacial strength by defining a characteristic length. An equation expressing the relationship between the characteristic length on the stress contour and the interfacial strength was derived, and validated using finite element analysis. The primary advantage of proposed measurement technique is that only a single fiber crack, which usually occurs within elastic deformation of matrix, is required for the evaluation of interfacial strength, whereas saturated fiber fragmentation is necessary in the conventional method. Herein, a sample application was demonstrated using a single carbon fiber and epoxy specimen, and an average interfacial strength of 23.8 MPa was successfully obtained