Marcin Kneć

Computational Models of Laminated Glass Plate under Transverse Static Loading

Laminated glass with Polyvinyl Butyral (PVB) interlayer became a popular safety glass for aircraft windows, architectural and automotive glazing applications. The very soft interlayer, bonding the glass plates, however, has negligible normal stress in transverse loading and it resists mainly by shear stress. The classical laminate theory obeying the principle of the straight normals remaining straight is not valid for laminated glass. Conventional Finite Elements (FE) are used to model the laminated glass in cylindrical bending to investigate the problem. Based on the assumption that the glass layers of a laminated glass plate obey Kirchoff’s classical plate theory and the PVB-interlayer transfer load by shear stress only, the differential equations of a Triplex Laminated Glass (TLG) plate are derived and a special TLG plate FE is elaborated. For each of its nodes, the element has one transverse translational, three rotational, and two additional degrees of freedom representing the slippage between the glass layers. All computational models are compared with experimental tests of a laminated glass strip in cylindrical bending.

Spot Welding–Adhesive Joints: Modelling and Testing

Modelling and testing of hybrid joints obtained by combination of two simple techniques, i.e., by application of spot welding and adhesive, is reported. The joints were subjected to uniaxial tension. The experiments were performed for: 1) a pure joining of the parts by spot welding and 2) spot welding–adhesive joining of the structural elements. A new experimental method was elaborated with application of two digital image correlation (DIC) systems. The method allowed for online monitoring of the deformation process of the joined elements with complex shapes. Modelling of the hybrid joints response to mechanical loading was performed by ABAQUS code. Damage process in the adhesive layer was taken into account. The obtained results lead to the conclusion that the strengthening of joints by the application of adhesive significantly improves static strength and energy absorption. The visible degradation process of the adhesive layer which started prior to the maximum value of force carrying the hybrid joint was obtained.

Determination of Flexural Properties of Rigid PUR Foams Using Digital Image Correlation

Cellular materials represent a new class of materials; main parameters that characterize the cellular structure are relative density, shape of the cell (open or closed), wall thickness and cell diameter. The purpose of this paper is to investigate the microstructure of foams materials and also to determine the flexural properties of this rigid PUR foams using Digital Image Correlation (DIC). The rigid PUR foams cells morphology and pore distribution for three densities (100, 145 and 300 kg/m3) were studied before testing through scanning electron microscopy. Determination of flexural properties was carried out on rectangular beam samples using ARAMIS 2D system. This method provides a substantial increase in accuracy for measuring strain and is based on the calculation of surface deformation using a set of digital images from undeformed stage to different deformed stages. The specimens were subjected to static three points bending tests with loading rate of 2 mm/min, at room temperature and loading was applied in rise direction of the foam. Experimental results show that main mechanical properties such as flexural modulus and flexural strength values increases with increasing of density.

Experimental determination of mechanical properties of aluminium foams using Digital Image Correlation

This paper presents an experimental characterization of three different types of closed-cell aluminium alloy foams (AlMg1Si0.6, AlSi12Mg0.6 and AlMg0.6Si0.3) under static compressive loading. This study was carried out on half-cylindrical specimens with skin. The influence of foam density on compressive behaviour was investigated for densities ranging from 430 kg/m3 to 935 kg/m3. The compression tests were performed at room temperature (23°C) with a constant crosshead speed of 0.5 mm/min. Strain distribution, yield stress and compressive modulus values were recorded using Digital Image Correlation. Experimental results show that the mechanical properties (Youngs Modulus, yield stress and plateau stress) increase with density.

Size Effect on Fracture Toughness of Rigid Polyurethane Foams

This paper presents the size effect on fracture toughness of polyurethane foams (PUR 40), with nominal density 40 kg/m3, closed-cell rigid foams widely used for sandwich cores. Determination of the fracture toughness was carried out by three-point bending tests (TPB), on notched specimens, at room temperature (20±2°C). To determine the size effect in Mode I fracture toughness, specimens geometrically similar in two dimensions with length-to-width ratio 5:2 were selected. The specimens were subjected to a quasi-static loading with a speed of 2 mm/min, which was applied exactly on the notch direction. A strong size effect in the closed-cell PUR foam is experimentally demonstrated, by considering a smooth transition between strength of materials approach (with no size effect) and asymptotic case of linear elastic fracture mechanics.

Fatigue Response of the Hybrid Joints Obtained by Hot Spot Welding and Bonding Techniques

Hybrid joining of structural parts (e.g. [3-1) is relatively new approach to create more safe and reliable connection of the critical part of engineering structures. In this paper we consider hybrid joint consisting of 2 aluminum stripes and an angle bar (e.g. [7]) joined by 2 simple techniques: hot spot welding (HSW) and adhesive bonding (AB). The samples were subjected to fatigue tests in order to find fatigue response at different level of load amplitude. New method of plastic deformation measurement during fatigue was proposed with application of Digital Image Correlation (DIC) method. Numerical analysis of the hybrid joint fatigue response was proposed in the paper taking into account both: gradual degradation of the bonding layer and plastic damage in the aluminium strips due to cyclic loading.

New method of determination of spot welding-adhesive joint fatigue life using full field strain evolution

Fatigue tests were conducted since more than two hundred years ago. Despite this long period, as fatigue phenomena are very complex, assessment of fatigue response of standard materials or composites still requires a long time. Quite precise way to estimate fatigue parameters is to test at least 30 standardized specimens for the analysed material and further statistical post processing is required. In case of structural elements analysis like hybrid joints (Figure 1), the situation is much more complex as more factors influence the fatigue load capacity due to much more complicated structure of the joint in comparison to standard materials specimen, i.e. occurrence of: welded hot spots or rivets, adhesive layers, local notches creating the stress concentrations, etc. In order to shorten testing time some rapid methods are known: Locatis method [1] - step by step load increments up to failure, Prots method [2] - constant increase of the load amplitude up to failure; Lehrs method [2] - seeking for the point during regular fatigue loading when an increase of temperature or strains become non-linear. The present article proposes new method of the fatigue response assessment - combination of the Locatis and Lehrs method.

Experimental Study of Bimaterial Shear Strength and Strain Concentrations by Iosipescu Based Test Using Digital Image Correlation System

Adhesive bonding of two different materials appears in many modern engineering applications, e.g.: airplanes, boats, cars etc. In many practical problems the adhesive bonding is subjected to shear loading. Therefore this is important to investigate the whole deformation process of the considered type of joints under monotonic loading, to get information about the shear strength and strain concentrations. Such concentrations lead to microdefects initiation and their further coalescence to create a main crack. The unstable crack propagation leads to final failure of the adhesive joint. The Digital Image Correlation (DIC) System - ARAMIS allows for constant monitoring of the deformation state up to the final failure. The tests were performed for bi-material specimens made of adhesively bonded PMMA and aluminum strips (Fig.1) and for pure PMMA and pure aluminum specimens. Additionally, two strain gauges on each homogeneous specimen and four on the bimaterial ones are used for strains estimations. The four point bending Iosipescu tests were performed using MTS machine with constant speed. In the first method (DIC) the ARAMIS system recorded a displacement distribution in samples with frequency 1Hz. In the second method the strains were recorded by the strain gauges - using analog output channels of the HOTTINGER data Acquisition System - MGCPlus, the current value of the load using analog output channel of the MTS machine was recorded too. The load-displacement curves were obtained for the whole deformation process and the shear strength of the joints was estimated. The energy absorption of the joints was calculated.