Using Ultrasonic Defectoscopy

One of the key methods of flaw detection is ultrasonic diagnostics. Experimental mechanics provides the ability to make precise measurements of the velocity of ultrasonic wave propagation, which helps to detect defects such as cracks, inclusions, and other anomalies in materials.

Using Stiffness for Materials Diagnostics

Experimental measurements of the stiffness of materials are key to flaw detection. Changes in stiffness can indicate deformations, defects, or other changes within the material. This allows the detection of not only mechanical defects, but also changes in the structure of the material.

Using Thermography to Detect Defects

Experimental thermography techniques based on measurements of thermal changes provide the ability to detect defects such as cracks or areas of reduced thermal conductivity. This not only helps in detecting defects but also helps in assessing their degree of criticality.

Acoustic Emission Measurement Methods

Acoustic emission methods record the sound waves emitted by materials when they deform. This is useful for detecting the initial stages of fracture or the development of defects such as cracks or corrosion.

Optical-based defectoscopy

Experimental optical defectoscopy techniques such as strain tomography and digital holography provide the ability to observe and measure strains in materials with high spatial resolution.

Use of Tensile and Compression Testing

Tensile and compression experiments provide data on the mechanical properties of materials. Anomalies in these properties can indicate the presence of defects. The use of accurate experimental data allows the strength and durability of materials to be assessed.

Experimental mechanics is becoming a key tool in the field of defectoscopy and materials diagnostics. Modern methods and technologies provide unique opportunities to detect and analyze defects, which in turn contributes to safer, more reliable, and more efficient materials and designs. Incorporating these techniques into engineering practices plays a key role in ensuring the quality and durability of materials in various industries.

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Definition of Boundary Conditions

Vibration measurements help engineers and designers to determine the boundary conditions for their projects. By analyzing the vibration spectrum, it is possible to determine which frequencies are most likely to occur and tailor the design to those conditions, ensuring durability and resistance to vibration.

Material Life Cycle Assessment

Vibration measurements play an important role in predicting and evaluating the life cycle of materials. Constant vibrations can cause material fatigue, which in turn can lead to cracks and deformations. Vibration analysis can determine how fast the fatigue process is occurring and when maintenance should be performed.

Energy Optimization

Energy efficiency is a key aspect in the design of machines and structures. Vibration measurement helps to optimize systems by considering their natural frequencies and resonances. This helps in reducing energy losses and creating more efficient and stable structures.

Designing with User Comfort in mind

In case of machines and devices designed for human use, vibration measurement becomes an important aspect of user comfort. Analyzing the effects of vibration on humans helps in designing more comfortable and safer products by considering physiological and psychological aspects.

Prevention of Destructive Resonances

Vibration measurements help to identify potentially dangerous frequencies and avoid resonances that can lead to destructive effects. This is important for creating structures and machines that can operate without significant damage over their entire life cycle.

Vibration measurements provide the data needed to create accurate mathematical models of system behavior. This helps engineers better understand the dynamic performance of structures and machines, which in turn facilitates the design and optimization process.

Vibration measurements have a huge impact on the design of structures and machines, ensuring their resistance to vibration and improving their efficiency and safety in use. With the use of modern technology and accurate measurement methods, engineers are creating more sustainable and efficient solutions that meet modern engineering requirements.

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The measurement method based on computer vision techniques described in this paper is derived from the need to measure the motions of scale models of offshore structures, which are typically developed and validated by the Laboratory for Dynamic Analysis of Structures and Signal and Image Processing (LADEPIS) from the Federal University of Rio de Janeiro (COPPE/UFRJ). This laboratory has developed a draft measurement methodology based on the acquisition and frame processing of television images corresponding to mechanical systems in vibration.

The basic idea is to characterize some spots on the surface of the mechanical system that differ from the rest of the image by differences in light intensity. These spots are called “virtual sensors” here. This expression is used in contrast to traditional sensors, such as accelerometers, which are commonly used to measure motions in experimental mechanics. Virtual sensors can be identified either by drawing small spots on the surface of a structural element or by gluing small pieces of paper or other type of adhesive material, making sure that the light intensity is significantly different from the light intensity of the rest of the image.

Virtual sensors have a number of advantages: their weight is amortized; they are easy to manipulate; they do not change the physical characteristics of the structure; they have no wiring; they cost practically nothing.

After the characteristics of the virtual sensors are determined, the image frames corresponding to the vibrating mechanical system are digitized and processed by a computer. The image elements (“pixels”) that correspond to the virtual sensor are then separated from the rest of the image by intervention, first by processing that enhances the contrast and then by bitwise analysis. the image stored in the computer’s memory. The position of the geometric center of the virtual sensor is then calculated for any frame of the image, and the actual movements of the structure are determined using a scaling factor that establishes a relationship between the pixel positions and the actual motion coordinates.

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Measurements are usually performed by PC-based automated testing systems.

Standard test equipment

Several conditioning devices (HBM and Sint) are available for displacement sensors (LVDT) and load cells.

Different types of load cells are available for forces in the range of a few Newtons to 100 kN. Load cells for specific measurements can be designed and manufactured. Temperature can be measured with thermocouples either in the cryogenic region (type K from -200°C) or at high temperature (type T up to 1200°C). Recording devices include: computerized data acquisition systems, XY paper recording devices, analog and digital oscilloscopes.

Long-term experience in strain measurement with electric strain gauges has been accumulated. Load cells made of both metal and non-metallic (mainly composite and ceramic) materials have been used to measure strain under various conditions, including fatigue loading or aggressive environments.

The laboratory is also equipped with digital image processing systems designed for automated measurements of strain distribution using optical methods of experimental mechanics.

Residual stress

In recent years, several experimental and theoretical measures have been developed in the field of residual stress (RS) measurement and modeling.

A technique based on the initial strain distribution (ISD) has been proposed to model the full RS field in a component. RS measurements to estimate the ISD were performed using a progressive slice and multiple strain gauge measurements. The method was applied to estimate RS in laser-welded wafers and clad components.

The hole drilling (HD) technique for local RS measurement has been applied in several activities. A portable, computer-controlled hole drilling device (from Sint) is also available for field measurements.

The HD technique has been the subject of extensive research activities aimed at extending the applicability of existing standards (mainly ASTM E837). In particular, the effect of plasticity on measurements was considered and a procedure was proposed to increase the current limit of applicability from 0.5 to 0.9 of the yield strength of the material. This procedure is currently being considered for inclusion as an Annex to the new version of ASTM E837. In this area, a new four-gauge socket has been proposed for high RS measurements.

A new analytical approach to solve the problem of variable RS thickness has also been proposed.

Ultrasonic applications

An ultrasonic (ultrasonic) device (from Panametrics) is available to detect cracks and damage in material and components. Different types of ultrasonic probes can be used for different materials (including metal and composites).

C-scan.

US devices coupled to a digital oscilloscope (from LeCroy) were the hardware basis for the C-scan device, designed and manufactured to create an automatic complete US response map for the airframe.

The C-scan device also includes a pair of stepper motors and a PC that controls the movement of the probe and receives the signal. This system can also be used to perform tomographic analysis, producing a three-dimensional map of the body.

The US device has been used to assess various types of damage in laminate composites under fatigue loading.

Optical grid method

Grid methods offer a means of measuring displacements and deformations directly on the surface of structural components. The technique consists of transferring a grid to the surface of the part and determining the position of the grid node points before and after deformation. The availability of digital image measurement systems has given a powerful impetus to the optimization of this technique. The laboratory is currently developing innovative automated meshing methods based on image processing that provide high accuracy and speed.

The automated meshing method has been applied to material testing, design optimization, and computer model comparison.

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Classical mechanics is a type of mechanics (a section of physics that studies the laws of changing the positions of bodies and the reasons that cause it), based on Newton’s 3 laws and Galileo’s principle of relativity. An important place in classical mechanics is occupied by the existence of inertial systems. Classical mechanics is divided into kinematics (which studies the geometrical property of motion without considering its causes), statics (which considers the equilibrium of bodies) and dynamics (which considers the motion of bodies.

Time in classical physics is a continuous quantity, an a priori characteristic of the world, not defined by anything. As a basis of measurement, a certain sequence of events is simply taken, about which it is considered undoubtedly true that it occurs at equal intervals of time, i.e. periodic. It is on this principle that clocks are based.

A body is a material object that has mass, volume and is separated from other bodies by an interface. A body is a form of existence of matter.

Force is a vector quantity, which is a measure of action on a body by other bodies or fields. A force is fully specified if its numerical value, direction and point of application are specified. Interaction can be realized both between directly contacting bodies (e.g., in impact and friction) and between distant bodies. The interaction between distant bodies is realized by means of gravitational and electromagnetic fields associated with them.

The developed complex consists of devices, they are also modules, the number of which depends on the purpose of the experiment. The “Main” module is the measuring center of the whole complex. In addition to the collection of logic on two inputs from the “Detector” modules and recording time in the memory buffer, the module automates the processes of input and output information, including switching the external load. The main task of the “Detector” modules is to detect the movement of the experimental body by IR beam. The module “Load Key” is used for physical impact on the experimental body. All modules are connected by cords of “Audio-Video” type with RCA sockets.

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Methodology

The interest in the problems of mechanics related to the structure and functioning of living systems, on the one hand, was due to purely practical needs associated with the need for more adequate and detailed knowledge of the structure and functions of the human body both in normal and in diseases, in order to be able to carry out various medical interventions in the most appropriate ways. On the other hand, the current level of development of the basic natural sciences has made it possible to begin systematic fundamental research aimed at identifying and understanding the basic laws (physical, chemical, mechanical, cybernetic in nature) of the structure, functioning and development of such highly sophisticated and highly reliable “machines” as living organisms, whose enormous diversity constitutes the Earth’s biosphere. Not as much is known about the workings of human, animal, and plant organisms, even the most common ones, as is usually thought, and this ignorance covers even the simplest, at first glance, questions. Often, the structure of an organ and its mechanical function are known in detail, but there is no detailed understanding of the mechanism of operation. It also happens that the structure of an organ and some of the processes that take place in it are known, but its general purpose is unclear. Finally, often due to experimental difficulties, the structure of an organ is poorly understood and, as a result, even the principle of its operation is unknown. Examples of such situations will be mentioned below.

Relationship to other sciences

While the application of natural sciences to the problems of modern engineering and technology has reached a high level of efficiency, and in fact, it comes down to the skilled use of well-understood primary laws, in biomechanics, it is necessary to first create a foundation for the development of fundamental knowledge, methodology and theoretical concepts, which will allow to bring the applied aspects to a corresponding high level. The theoretical methods of biomechanics are based on the achievements of modern mechanics, which studies mechanical motion itself in connection with physical, chemical and electromagnetic phenomena and using the appropriate mathematical apparatus and computer technology. Experimental biomechanics combines the methods of mechanics with those developed in biology and medicine. One of the most responsible and time-consuming aspects of biomechanics is the systematization and analysis of large amounts of observational data accumulated in biology, the translation of vague verbal descriptions into mechanical terms and, whenever possible, into formal mathematical constructions. The latter are needed not so much for quantitative calculations as for qualitative judgments. Biomechanics is closely related to other areas of life science; for example, to theoretical biology, bionics and bioengineering, biocybernetics, biotechnology, ergonomics, physiology, etc.

Organization of research

Research in biomechanics is conducted in all developed countries. Specialized research institutes operate in the United States, Germany, Japan, Canada, Italy, and a number of other countries. A wide network of biomechanics laboratories exists in most leading universities in the United States and European countries, in large industrial associations and clinics. Especially numerous are the research groups that provide physiological and medical programs of biomechanics. Such research has been significantly developed in Bulgaria, Czechoslovakia, and Poland, where specialized research institutions have also been established. The International and European Societies of Biomechanics, a number of national societies and societies uniting biomechanics researchers of a narrower profile are actively functioning.

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Distributed Fiber Optic Sensor (DFOS) technology

DFOS is a new stage in the measurement of strains and stresses in materials. These fiber optic sensors are distributed over the surface of an object and provide high spatial resolution, making them valuable for real-time strain monitoring on complex structures such as composites and building structures.

Integrated sensors using nanomaterials

With advances in nanotechnology, integrated sensors based on nanomaterials are becoming more common. Graphene sensors, for example, have unique strain sensitivity, making them useful for measuring minute changes in the structure of materials.

Development of digital holography techniques

Digital holography provides the ability not only to measure strains but also to visualize three-dimensional shapes of objects in real time. This is important for analyzing the behavior of materials under load, as well as for developing more accurate numerical models.

Wireless technologies for data acquisition

The use of wireless sensors and data acquisition devices greatly simplifies the experimental measurement process. This is especially important when working with large structures or in environments where wiring is limited.

Microstructure research technologies

With the development of microscopy and image analysis techniques, researchers can now study the microstructures of materials at the micro level in greater detail. This allows data on internal strains and mechanical properties to be obtained at lower levels.

The application of machine learning techniques to analyze and process data opens new horizons in research. Algorithms can automatically identify patterns and relationships, improving the accuracy and speed of analyzing experimental data.

New tools and technologies in experimental mechanics are redrawing the picture of what we can achieve in engineering research. These innovations not only improve the accuracy of measurements, but also enhance the research capabilities in materials and structures. In the future, as technological advances increase, expect even more exciting developments that will continue to shape the future of experimental mechanics.

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Plastics are lightweight, economical, and preferred alternatives to metals in many applications. Plastics have low mechanical and wear properties compared to metals, so they are reinforced with fillers and fibers to improve their mechanical properties. Composite materials provide the ability to combine different properties and materials to design for applications that require multiple functionalities. As a result, there is a growing interest in the development of new polymeric materials, especially in improving their mechanical properties, such as tensile strength and tensile modulus. These properties can be further enhanced by reinforcement. The properties of such a composite can be influenced by the type of reinforcement, the shape of the reinforcement, and the distribution of the reinforcement in the polymer matrix. Nanocomposites are emerging as a new class of composite materials in which one of the reinforcing phases is in the range of 1-100 nm. Recent studies of nanocomposites have revealed significant improvements in mechanical, tribological, and thermal properties without increasing the density of the nanocomposite. The property improvements are due to the high strengthening efficiency of these nanoparticles due to the large aspect ratio and improved interaction between the nanoparticles and the matrix. A number of researchers have investigated the effect of zeolite on the mechanical properties of polymer nanocomposites. The addition of 5 wt% nano-zeolite to polyurethane improved the tensile strength and Young’s modulus. Lv et al. investigated the effect of modified zeolite on the nucleation properties and mechanical properties of polypropylene. The results showed an increase in tensile and flexural strength and nucleation effect due to the addition of 0.3 wt.% zeolite to the base polymer. In addition, the addition of zeolite to high-density polyethylene (HDPE) increased the impact strength to failure.

Polyamide 6 (PA6) is widely used as an engineering plastic due to its excellent mechanical properties, tribological characteristics and chemical resistance. 12 polyamide 6 nanocomposites have been successfully fabricated and exhibit excellent mechanical properties. One of the main drawbacks of polyamides is their water absorption. Absorbed water in polyamide has a great impact on the mechanical properties and dimensional characteristics of molded parts. It can reduce the tensile modulus and strength. Adding glass fibers to PA6 resulted in an increase in water absorption resistance. However, the addition of glass fibers increases the melt viscosity, which can cause difficulties when molding thin-walled parts. Additionally, the abrasive nature of glass fiber can wear away at the screw and barrel of the injection molding machine. Therefore, the balance between the stiffness and toughness properties of the polymer has attracted the attention of researchers. The strategy of using rigid spherical nanoparticles as stiffening agents has been the topic of extensive research because it could strengthen and stiffen polymers at the same time. The addition of nano-CaCO3 particles to PA6 improved mechanical properties and reduced water absorption.

The incorporation of nano-zeolite as a spherical nanoparticle into the PA6 matrix can improve the stiffness and strength properties at the same time. The main objective of this study is to characterize PA6 without compromising the mechanical performance and ease of processing by blending PA6 with nanosealite particles.

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⦁ Carbon/graphite;
⦁ SiC;
⦁ Oxide;
⦁ TRISO fuel particles/seals;
⦁ New materials for nuclear fuel cladding;
⦁ MAX phases.

Unique and advanced methods have been developed to study these materials at multiple scales. The goal is to correlate the nano/microstructure of material processing with macroscale damage and fracture under in-service conditions.

EMAM has established strong collaborative links with key national and international players in the nuclear fission, nuclear fusion and aerospace industries. The goal is to use scientific approaches to gain a mechanistic understanding of the failure modes in these materials. As a result, their industrial applications are supported.

There are active ongoing projects in the following areas with open opportunities for doctoral and postdoctoral students.

• Mechanistic understanding of damage and fracture of ceramic-matrix composites under extreme conditions: Working with many industries and processing groups, this area studies a range of aerospace and nuclear fission/synthesis CMUs in terms of their local mechanical and thermal properties, residual stresses, deformation and fracture, including crack initiation and propagation from ambient temperatures to above 1000°C by in situ imaging and diffraction techniques;
• Damage and Fracture of Nuclear-Graphite Composites at Multiple Length Scales: This topic studies a wide range of polycrystalline graphite materials, from highly oriented pyrolytic graphite to fine/medium/coarse graphite composite, unirradiated or irradiated with ions, neutrons or protons, to understand their multiple length-scale structure, physical properties before and after irradiation, at ambient temperatures and up to 1100°C;
• Thermal and Mechanical Characterization of TRISO Fuels: This program investigates a range of tristructural isotropic nuclear fuel (TRISO) particles, either free-standing or embedded in a SiC or graphite matrix, in terms of their local properties, residual stresses, and high-temperature mechanical properties that vary with processing parameters;
• Interfacial strength of heterogeneously integrated ceramic films. A number of micromechanical test methods have been developed to evaluate the interfacial toughness of thin ceramic films (e.g., GaN) integrated onto rigid substrates, including SiC, Si, and mono/polycrystalline diamond. to enable the development of new semiconductor materials for high-power radio frequency (RF) devices.

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As a rule, the program provides a stepwise application of loads for several design cases. The combination of loads, their magnitudes, the order of application by design cases, ultimate and subcritical strength conditions or the achievement of ultimate deformations (displacements) are set in a table, ribbon or three-dimensional graph.

Each design loading case is divided into two levels: operational and design. The operational level of loading is divided into 6 – 10 stages to perform preliminary measurements of displacements and VAT in the elastic region and simultaneous development and control of reproducibility of linear loading. At this level, the zones and cross-sections of possible failure or plastic hinge occurrence are determined on the basis of the VAT study.

Observation areas are marked during testing before fracture, remote instrumentation for measuring parameters at fracture is installed and graded. Depending on the task, optical, polarization-optical, moiré (raster) means of VAT registration are installed, high-speed photo and movie registration, videorecording of fracture dynamics or loss of stability by stages are used. Special safety measures are taken into account, especially when testing high-strength brittle materials and for objects accumulating significant elastic energy before fracture, for example, when testing shells of large volumes by compressible gas (air) supercharging.

Loading to design loads is carried out once, continuously increasing the load level from operational to design, and, without stopping the loading, bring the test to the maximum loads, noting a sharp (or smooth) decrease in load at failure of elements, loss of bearing capacity (stability). The rate of loading is stipulated in the program and in the specifications for the energy requirements of the stand. For static loading of metal structures, the critical speed is when the error of load reproduction due to the attached masses of the loading system becomes greater than 1% of the given current force value, and all transients from the beginning to the end of the deformation diagram depend only on the stiffness of the system, not on its mass.

In the case of carrying capacity tests with simultaneous thermal effect on the object, carried out by means of radiant heating or in chambers-thermostats, the modes of mechanical loading and heating (heating) rates are set by special schedules, taking into account the heat capacity of the specimen and the system, inertia of heat transfer regulation, dissipation and power of radiators. The program is implemented by an automatic system of output and maintenance of the temperature regime on the object in time or as a function of mechanical load. The methodology of carrying capacity testing of scale models of large-scale objects requires a rigorous theoretical justification and considerable research.

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