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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