Emerging Methods in Mechanical Behavior

How microscopic stress and strain analysis can improve the understanding of the interplay between material properties and variable amplitude fatigue

As a representative method of optical non-interference measurement, digital image correlation (DIC) technology is a non-contact optical mechanics method that can measure the displacement and deformation of the whole field. However, when the measurement range of the field is too large, the existing DIC method cannot measure the full-field strain accurately, which limits the application of the DIC measurement in the case of a large size and wide-field view. To address this issue, a DIC measurement method for large-scale structures based on adaptive warping image stitching is proposed in this paper. First, multiple adjacent high-resolution images are collected at different locations of large-scale structures. Secondly, the collected images are stitched by applying the adaptive warping image stitching algorithm to obtain a panoramic image. Finally, the DIC algorithm is applied to solve the whole deformation field. In the experiments, we first verify the feasibility of the proposed method for image matching and fusion through the numerical simulation of a rigid body translation experiment. Then the accuracy and robustness of the proposed method in practical application are verified by rigid body translation and a three-point bending experiment. The experimental results demonstrate that the measurement range of DIC is improved significantly with the adaptive warping image stitching algorithm.

Time-varying damage evolution of concrete under cyclic disturbance loading- an experimental observation utilizing AE and DIC

Editorial

Digital image correlation (DIC) is a powerful technique for determining material deformation and damage and currently is viewed as a potential method to study failure and crack propagation in advanced composite materials. Case studies in concrete, epoxy adhesives, and carbon/epoxy laminates demonstrate the effectiveness of the DIC technique in visualizing crack propagation. This review highlights the applications, challenges, and implementation of the DIC technique in the failure and crack propagation of fibre-reinforced polymer (FRP) composites. The important factors such as field of view, speckle pattern, and algorithm choice are discussed while emphasizing the need for careful selection and calibration. The review concludes by highlighting the significance of crack propagation studies for composite behaviour and the role of DIC in calibrating and validating models of composite failure analysis. Future research directions include investigating mixed-mode delamination, improving calibration procedures, assessing DIC accuracy for large deformations, and comparing different DIC algorithms, which are discussed.

Neutron scattering is one of the most powerful characterization techniques available for materials research, and its proven capabilities and anticipated potentials justify the 1.4-billion dollar construction of the Spallation Neutron Source (SNS) at the Oak Ridge National Laboratory (ORNL) as well as a number of multi-million dollar facility upgrades at the Los Alamos Neutron Science Center (LANSCE), Intense Pulsed Neutron Source (IPNS), and High Flux Isotope Reactor (HFIR) in the US, and at ISIS, the Rutherford Appleton Laboratory in UK. However, while the multi-billion dollar constructions are on-going all around the world, currently there is no concerted effort within the US in advancing the science and education in the application of neutron scattering in materials research, specifically in the study of mechanical behavior of advanced materials. To be better positioned in the scientific research at the international level, it is important to develop a network with international counterparts. Therefore, a group of the most active researchers in the neutron-scattering materials-research field will form an international network through the International Materials Institutes (IMI)-Advanced Neutron Scattering netWork for Education and Research (ANSWER) with a focus on mechanical behavior of materials. The IMI provides a synergistic effort in advancing the fundamental understanding of mechanical behavior of materials at the atomic level using state-of-the-art neutron sources in the world.

The principles and examples of state-of-the-art experimental methods for measuring the fracture mechanics parameters are presented in this paper. The methodology of experimental analysis of the fracture mechanics parameters includes investigation of fracture behaviour of metallic materials using modified specimens with initial crack under tensile load, with the primary goal of determining the characteristics of fracture processes for the case of thin plates, using basic fracture mechanics postulates. The methodology also includes the application of experimental fracture mechanics procedures as defined by standards, using three-dimensional stereo-metric mechanical behaviour measurement methods. Fracture behaviour of metallic materials, mainly 316L stainless steel and titanium alloy Ti-6Al-4V specimens, is analyzed by using a digital image correlation (DIC) system for measuring strain and displacement in the material. GOM three-dimensional optical system and Aramis software are used to perform experimental analysis of selected specimens. As this system is used to measure strain and crack tip opening displacement (CTOD) parameter on the modified compact tension specimen C(T) and notch specimens, a basic review of measuring procedures and result processing is given, alongside other possible applications for this system. The presented results show strain and displacement fields during crack tip opening, crack growth, and the moment of fracture of specimens, which are not possible using traditional measurement methods. The analysis of results shows that it is possible to measure displacements during crack tip opening with a great precision, and thus obtain the CTOD parameter. The results show that the selected measuring method obtains good results in the analysis of mechanical behaviour and fracture mechanics parameters of metallic materials.

Investigation of the impact of fiber incorporation on the properties of high belite cement

. Production efficiency as well as the reduction of energy consumption and waste are the main drivers for the improvement of large-scale production in chemical industry. In addition, the demand for new processes – these days especially related to the chemical energy conversion as basis for the Energiewende – are additional triggers for innovation. Catalysis, well recognized by the public e.g. in form of the 3-way automobile catalyst, plays an important role for about 90% of all processes in chemical industry. The development of new and improved catalysts is a challenge for chemists – as is the search for new structural materials for mechanical engineers. Due to the often-necessary noble and thus expensive metals (e.g. palladium) in many catalysts, structural and chemical function have been developed separately in the two communities. Recent progress in catalytically active materials allows replacing expensive noble metals in selected catalytic processes by significant cheaper elements [1]. This offers the new perspective to combine structural and chemical functionality by innovative materials. Within this area, intermetallic compounds with their peculiar combination of crystal and electronic structure [2], represent an interesting class of materials to address this vision as will be shown in the contribution.

Anisotropic mechanical properties and deformation behavior of low-carbon high-strength steel component fabricated by wire and arc additive manufacturing

The authors present a new approach, fibDAC, which allows to measure and analyze deformation fields on stressed micro and nano components, which can be utilized for mechanical material characterization. The method bases on digital image correlation (DIC) algorithms applied locally to load state images captured from focused ion beam (FIB) equipment. As a result, deformation fields are determined, which occur due to loading of microsystem structures inside the focused ion beam system. A similar tool, called microDAC/nanoDAC, has been reported earlier and applies DIC techniques to SEM or AFM images. The advantages of the new fibDAC approach occur in the incorporation of specimen preparation like ion milling, ion beam surface polishing and DIC patterning as well as specimen loading by ion milling and DIC deformation measurement in a single equipment. Combining measured fields with finite element simulations or analytical solutions of the corresponding mechanical problem, relevant mechanical material properties can be evaluated. Corresponding object loading is accomplished either externally by testing modules designed for application inside the FIB equipment or by ion milling on the test specimen. As an example ion milling on specimens with residual stresses is demonstrated. Released in this way residual stresses cause object deformations nearby the milling area. Measured deformation fields by fibDAC allow to evaluate very local residual stresses. Some principal experiments illustrate the feasibility of the chosen approach. Features and challenges connected with this new method are discussed in some detail.

In-situ straining experiments and residual stress evaluations by micromachining require accurate measurement of the surface displacement. These can be conveniently achieved by Digital Image Correlation (DIC). Three surface decoration techniques are presented to enhance surface deformation and residual stress measurement capabilities on micron-scale samples within a Scanning Electron Microscope – Focused Ion Beam (SEM-FIB) instrument. They involve the use of yttria-stabilized-zirconia nano particles applied chemically, nano platinum dots applied using FIB, and Focused Electron Beam (FEB) assisted deposition. The three decoration techniques create distinctive, random surface features that can be used with Digital Image Correlation to provide full field maps of surface displacements at high magnifications. A series of experiments using a FEGSEM /FIB demonstrated the effectiveness of the three surface decoration techniques for FEGSEM imaging at magnifications from 2,000× to 60,000×. The resolution of the image correlation is substantially enhanced by the surface decoration, with displacement standard deviations reduced to the 0.005 – 0.03 pixel range, depending on the patch size used. The implications for displacement measurement at the micro- and nanoscale are discussed and some examples shown.KeywordsScanning electron microscopyFocused Ion BeamHigh magnifications2D digital image correlationSurface decoration methodsResidual stressSubmicron scale

Mechanical behaviour of weakly filled granite and a unified evaluation method for macro-fine-micro multi-scale fracture characteristics

Ultrafine-grained CrMnNi steels: Lueders phenomenon and texture inheritance

An experimental procedure is conducted to investigate the mechanism of the non-monotonic characteristic between curing temperature and mechanical behaviors of the Kevlar/epoxy composite in macro and micro levels. Different specimens are fabricated at four different curing temperatures and tested with ±45° off-axis tensile loading on a universal test machine coupled with digital image correlation (DIC). Moreover, the environmental scanning electron microscope (SEM) was used to obtain the micrographs and reveal their mechanism. The tested results show that the tensile mechanical behaviors are sensitive to the curing temperature and the relationship is non-monotonic. Also, as the temperature increases, the thicknesses of the specimens are significantly enlarged. By analyzing the SEM micrographs of the matrix grooves in the damage zone and DIC strain contours, it is concluded that the non-monotonic relationship is dominated by the properties of the Kevlar/epoxy interfaces and deformation of the distorted fibers.