Papers by Keyword: Digital Image Correlation (DIC)

Abstract: Notched fiber-mental laminates are susceptible to damage. Nowadays, damage detection mainly depends on visual inspection and C scan. But the two methods are limited to the technical skill of the inspectors, causing missed detection or even fault detection. This paper devotes to exploring the DIC monitoring technique to assess of the damage process taking place in notched (open hole) specimens under uniaxial tensile loading. Two-dimensional (2D) Digital Image Correlation (DIC) techniques are employed to obtain full-field surface strain measurements of GLARE3-3/2 and GLARE6-3/2 laminate with an open circular hole under tensile loading. Failure modes,damage initiation and progression of notched fiber-metal laminates are characterized and discussed.

Abstract: In scope of the investigation of residual stresses the hole drilling method is an accepted method. The method is though not applicable for materials with high anisotropic behavior. Therefore a new algorithm is derived which allows the calculation of residual stresses in laminates made of unidirectional layers. Also the strain gauges deliver only strains on the areas where the strain gauges are applied. With the use of a high resolution imaging system and digital image correlation this area and the informational output can be widely improved. First, the derivation of the residual stress analysis algorithm is presented. For this an adequate finite element model, which is modeling the cooldown process as well as the drilling process, is set up and the surface strains are extracted. Based on this information an algorithm is derived and presented. Within the derivation a change of the layup, a possible change of the cooldown process and a variation of the drilling steps can be investigated. In consequence the input parameters of the algorithm can vary dependent on these factors. Second, the new optical testing setup with refinements to be able to measure the small deformations within micro-strains on the specimen’s surface is prepared and the concept presented. To solve the problem of casting shadows of the drill a special camera setup is being used.

Abstract: Numerical models based on cohesive zones are usually used to model and simulate the mechanical behavior of laminated carbon fiber reinforced polymers (CFRP) in automotive and aerospace applications and require different interlaminar properties. The current work focuses on determining the interlaminar fracture toughness (G_IC) under Mode I loading of a double cantilever beam (DCB) specimen of unidirectional CFRP, serving as prototypical material. The novelty of this investigation is the improvement of the testing methodology by introducing digital image correlation (DIC) as an extensometer and this tool allows for crack growth measurement, phenomenological visualization and quantification of various material responses to Mode I loading. Multiple methodologies from different international standards and other common techniques are compared for the determination of the evolution of G_IC as crack resistance curves (R-curves). The primarily metrological sources of uncertainty, in contrast to material specific related uncertainties, are discussed through a simple sensitivity analysis. Additionally, the current work offers a detailed insight into the constraints and assumptions to allow exploration of different methods for the determination of material properties using the DIC measured data. The main aim is an improvement of the measurement technique and an increase in the reliability of measured data during static testing, in advance of future rate dependent testing for crashworthiness simulations.

Abstract: In order to optimize the design of vibrating screening machines and realize significant weight reductions, the use of hybrid structures is gaining importance. In this context, the joining of FRP and steel and their interactions due to different material properties were investigated. Therefore, quasi-static tests with combined mechanical and thermal loads were carried out. To realize the simultaneous application of physical measurement techniques, e.g. optical and acoustic measurements, and thermal loads, short-wave infrared emitter technique was used instead of thermal chambers. Thus, the mechanical characteristics and acoustic emissions could be determined and assessed. The results show different structural mechanisms of hybrid joining at room and elevated temperatures. The characteristics of failure modes, shear stresses, strains and acoustic emissions could be correlated to determine the damage developments and mechanisms.

Abstract: This paper demonstrates a unique application of DIC wherein the structural performance and structural integrity have been evaluated together almost in real-time. The results obtained from the ground level tests, simulating the bonding between the TPS to the base structure of a space crew module, are reported to find the adequacy of two different adhesives prior to actual bonding. The test objective was to characterize the adhesives based on the structural performance (deflection and strain behavior) of the TPS and conduct health monitoring in real-time (i.e. abort the test whenever the TPS fails). The dual objective could be met using DIC in a full-field and non-contact manner, which was essential due to the limitations of the contacting type measurements.

Abstract: In order to develop a constitutive material model and to verify its consistency when implemented in a computational code, it is necessary to understand the material and to carry out a comprehensive experimental analysis. This can be a challenging task in the case of composite materials and structures, such as masonry, when using conventional measurements. Strain gauges and allow recording strains at a limited number of discrete points and do not provide sufficient amount of data, thus increasing the cost of the analysis. From that reason a full-field non-contact measurements, such as Digital Image Correlation (DIC), became very popular and valuable for analysis of structures subjected to mechanical loading and precise detection of the onset of strain localization. The presented study deals with tracking the strain localization using DIC in the case of masonry piers loaded by the combination of bending and compression. In such case the strain localizes into more compliant mortar joints while the complete collapse occurs when the masonry blocks fail to transfer tensile stress due to transversal expansion. The obtained data will be used for the validation of a finite element model to predict the behavior of masonry structures.

Abstract: The contribution deals with the investigation of the influence of facet size and smoothing on the results obtained by low-speed digital image correlation (DIC) system by strain analysis performed on specimen with a small hole loaded by tension loading. In conclusion the obtained results are verified by a numerical solution using finite element method.

Abstract: Paper deals with the identification of coupled mode shapes by experimental modal analysis. Main attention is focused on the using of Complex Mode Indicator Function that is based on singular value decomposition of frequency response function matrix and allows to separate coupled and also closed modes. In the paper there is described experimental modal analysis at which digital image correlation method is used to measure responses of a circular plate. The measurement was evaluated in program Modan 3D that is being developed by the authors.

Abstract: Biaxial tension test of the cruciform specimen of styrene-butadiene rubber is described in this paper. The rubber layer is a part of the conveyor belt used for the transportation of coal. The specimen are loaded by the home made biaxial testing device. The big deformation of specimen are determined by the Digital Image Correlation. The parameters of Mooney-Rivlin hyperelastic material were determined. Numerical simulation of the biaxial test was performed in Comsol Muliphysics.

Abstract: Joining aluminium alloys with the use of welding techniques often impairs their strength properties and in some cases it is very difficult or even impossible. An alternative method for joining this type of material is friction welding including FSW welding. The airplane aluminium alloy 2024-T3 is an example of material that can be welded using this method. Heat emitted during the process, which contributes to the material plasticisation in the zones of welding, causes significant changes in the material structure, thus affecting the joint properties. Fatigue life calculations of this type of joint can be performed according to different approaches. One of them is a local approach which requires knowledge of local strains or stresses within the notch zone. This paper is a presentation of exemplary results of experimental and numerical tests of strain in the zone of notch that occur in a joint under time variable loading.