Intelligent composite material-"life intelligence" aerospace profile

Source: Tomorrow’s information? In the past, the field of composite materials was basically a unified situation of structural composite materials.
It has been gradually changed by functional composite materials, and functional composite materials are also developing in the direction of multifunctional composite materials, making materials more than one A structure, but also has functions or a variety of comprehensive functions
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? Smart composite materials are materials that can sense changes in the environment, draw conclusions through self-judgment, and execute corresponding instructions autonomously
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It has the three elements of life intelligence: perception function (monitoring of stress, strain, pressure, temperature, injury), judgment and decision-making function (self-processing information, discerning the cause, drawing conclusions) and executive function (self-healing and self-injury Change the stress and strain distribution, structural damping, natural frequency and other structural characteristics), which integrates sensing, control and driving functions, can sense and respond to changes in the external environment in a timely manner, make judgments, issue instructions, and execute and complete actions to make the material possess Self-detection, self-diagnosis, self-monitoring, self-healing and self-adaptive capabilities are important developments in composite material technology, and their development will comprehensively improve the design and application of composite materials
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? Smart composite materials usually integrate sensor materials and actuation materials tightly into prepreg plies, wet sheet plies, fiber placement, fiber winding, and resin transfer molding (RTM) during the molding process.
In terms of materials, at the same time, through the integrated controller, the composite material can self-diagnose, adapt and self-heal while bearing the mechanical load, and realize the intelligentization of the composite material
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? Structural monitoring technology can measure the strain, temperature, and cracks inside the composite material component in real time, and detect its fatigue and damage, so as to realize the monitoring of the structure and the prediction of the life
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For example: monitoring the structural damage that may occur during the manufacturing, processing, transportation, and storage of the composite material structure, and timely detection of possible matrix and fiber fracture, delamination, debonding of the inner lining layer and the composite material layer, and impact injury
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? At present, some advanced countries use optical fiber smart materials and structures to perform state monitoring and damage estimation of composite materials, that is, to embed optical fiber sensors or their arrays in key parts of the material or structure for real-time monitoring, damage assessment and life prediction throughout the life cycle
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? The American Acellent Technology Company conducted research on the structural integrity monitoring of solid rocket motors and liquid fuel tanks
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The tested fiber-wound composite container has a diameter of 380mm and a length of 500mm
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8 straps are embedded in the shell at equal intervals in the circumferential direction.
Each strap has 5 piezoelectric sensors with a diameter of 6.
4mm and a thickness of 0.
25mm at approximately equal intervals.
The 40 sensors roughly form a square grid with equal intervals.
Among them, 4 straps are buried in the circumferential winding layer of the aluminum lining, 4 are buried under the surface winding layer, and the shell is solidified after the winding is completed
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Use a ball hammer to impact a damage of about 12mm in diameter, compare the sensor signals before and after the detected damage, and normalize the distance of each sensor.
Combine the signal diagrams to show the approximate location and damage of the impact.
The degree of damage
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? Germany's ECHE and others have developed a space distributed sensor network system based on 12 FBG sensors for the health monitoring of the x-38 aircraft body structure
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The FBG sensor is pasted on the surface of the back components of the X-38 aircraft to monitor the mechanical load and thermal load of the spacecraft during launch and return
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By measuring the spatial temperature distribution and strain of high-load structural components, the remaining life of the main structural components of the aircraft can be estimated, and the health monitoring of the aircraft can be realized
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Japan’s TOSHIMICH and others have used piezoelectric ceramic (PZT) actuators/FBG sensors to monitor damage to the advanced composite structure of a new generation of spacecraft
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In order to monitor the damage that occurs inside the composite material of the spacecraft, the FBG sensor receiver is embedded in the carbon fiber-reinforced resin laminate structure, and the actuator is used to emit elastic waves
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When there is damage in the propagation direction of the elastic wave, the strength of the elastic wave will attenuate and the wave speed will change, which can detect the existence of damage
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? Under the influence of external stress and other environmental factors, the material will inevitably produce cracks and other damages, which will cause performance degradation; the accumulation of damage will also cause material failure
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The use of traditional repair techniques such as mechanical connection, plastic welding and adhesive bonding can repair the visible cracks of the material, but the traditional repair technology can no longer be used for the microscopic damage inside the material, so it is necessary to find a suitable repair method to improve the overall performance of the composite material And safety and reliability
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? At present, it is mainly divided into two types, one is implanted self-healing composite materials; the other is in-situ self-healing composite materials
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The former is a composite material that can give the material self-healing functional components under certain conditions by embedding in the matrix material.
Once the material has defects, it can imitate the principle of biological damage healing.
The embedded material components are under pressure, heat, etc.
Under certain conditions, the repairing agent is released.
This repairing agent can flow to the damaged surface, and it can polymerize when contacting with the catalyst in the matrix material to achieve the purpose of bonding cracks
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The latter refers to a special composite material that can repair itself under certain conditions without adding any restorative media to the matrix material
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Zako M et al.
studied the microcapsule epoxy resin system, using small thermoplastic particles (50um) impregnated with adhesive to fill the glass fiber/epoxy composite material.
When the composite material is damaged, it is embedded in the composite material.
The thermoplastic particles are heated at 120°C for 10 minutes to melt.
The load-displacement curve and tensile fatigue test in the three-point bending test show that the strength after repair is almost restored to the level before the damage, fully demonstrating the effect and potential of self-repair
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? Shape memory composite material has a shape memory function.
When the shape of the material changes due to changes in external conditions, the shape of the material can be restored by itself as long as the external conditions are restored to the initial state.
It has a large recoverable strain, high reliability, The advantages of low density, high specific stiffness, high specific strength and low cost
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? The unique properties of shape memory composite materials are particularly suitable for aerospace structures.
It integrates structural components and extension mechanisms.
The unfolding process can be achieved by heating, without the need for motors, bearings, position sensors, and complex electronic control devices and software
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It is based on the orientation and distribution of molecular chains in polymer materials, that is, internal intermolecular interactions, rather than martensitic transformation
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The elastic memory composite material can be made by conventional composite material technology.
After curing and forming, its mechanical properties are close to ordinary high-performance composite materials.
The difference is that when the temperature rises above the glass transition temperature, it exhibits low modulus and high failure strain.
, It can be rolled and folded according to various design requirements, and the shape will not change after it drops below the glass transition temperature
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When heated again to higher than the glass transition temperature, because the polymer matrix has a memory function, the material will return to the shape of the initial curing without applying any external force
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As the temperature changes, the process can be repeated without affecting the properties of the material
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? The demand for structural vibration reduction in the aerospace field is more urgent.
Because of the increase in the geometric size of large space structures and the large number of light structures with small damping, the vibration frequency and the control frequency are getting closer and closer, even partially overlapping, and accompanying vibration is inevitable.
This has become an important issue in the practical application of space structures
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Both passive control and active control can be used to suppress structural vibration
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Piezoelectric materials are one of the most used sensing and driving elements.
By embedding piezoelectric sensors, structural vibration information is obtained.
In this process, electrical energy is consumed through load resistance and partial vibration suppression is achieved
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