Применение акустической микроскопии для изучения упругих свойств и микроструктуры композитных материалов, армированных углеродными волокнами

• Автор: Лю Сунпин
• Шифр специальности: 01.04.06
• Научная степень: Кандидатская
• Год защиты: 2004
• Место защиты: Москва
• Количество страниц: 176 с. : ил.

CONTENT
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INTRODUCTION
1. CARBON FIBER-REINFORCED COMPOSITE MATERIALS AND ULTRASONIC METHODS OF THEIR INVESTIGATION
1.1. Structural organization of carbon fiber-reinforced composite materials
1.2. Methods for characterizing and evaluating CFRC materials
1.3. Ultrasonic techniques to measure elastic properties of CFRC materials
1.4. Defects and inhomogeneities in CFRC materials and methods of their studies
1.5. Methods of ultrasonic characterization and NDT&E for CFRC materials
2. PRINCIPLES AND FACILITIES TO STUDY MICROSTRUCTURE AND LOCAL PROPERTIES OF CFRC MATERIALS WITH HIGH-FREQUENCY FOCUSED ULTRASONIC BEAMS
2.1. Convergent ultrasonic beams and their interaction with plane-parallel objects
2.2. Principles of ultrasonic imaging with focused ultrasonic beam (acoustic microscopy)
2.3. Quantitative methods of acoustic microscopy — their applications in sound velocity measurements
2.4. Experimental set-up and specimens
3. INVESTIGATION OF LOCAL ELASTIC PROPERTIES OF CFRC LAMINATES AND THEIR STRUCTURAL ELEMENTS BY MEASURING SOUND VELOCITIES
3.1. Interaction of elastic waves with CFRC ordered structural media — sonic velocity measurements in low-frequency and high-frequency range
3.2. Measurement of local elastic properties of free single elements
3.3. Measurement of local elastic properties by microacoustic technique for
diverse kinds of CFRC materials
3.4. Measuring local elastic anisotropy of individual structural elements within CFRC laminate
4. STUDIES OF BULK MICROSTRUCTURE AND DEFECT NDE OF CFRC
MATERIALS BY USING MICROACOUSTIC IMAGING TECHNIQUE
4.1. Specific features of ultrasound reflection and mechanisms of acoustic contrast in CFRC laminates
4.2. 3D Acoustic imaging method for CFRC laminates
4.3. Bulk microstructure characterization and structural flaw NDE of unidirectional CFRC laminates by using multiple types of acoustic imaging
4.4. Studies of bulk microstructure and small-sized defect NDE in multi-directional CFRC laminate
5. BULK MICROSTRUCTURE CHARACTERIZATION OF WOVEN CFRC
MATERIALS BY USING MICROACOUSTIC IMAGING TECHNIQUE
5.1. Microstructural features of woven CFRC laminates and acoustic principles in their imaging
5.2. Studies of bulk microstructure of plain woven CFRC laminates by using multi-scanning acoustic imaging method
5.3. Studies of bulk microstructure of unidirectional tape CFRC laminate by using multi-scanning acoustic imaging method
CONCLUSIONS
PUBLICATIONS
REFERENCES

Introduction
[Actuality]: Carbon fiber-reinforced composite (CFRC) laminates belong to the class of reinforced composite materials whose elastic and strength properties are specified by properties of comprising components - resin matrix and reinforcement as well as spatial structure formed by reinforcing components in the matrix body. CFRC laminates consist of microscopic plies (100 -s-150 pm). Plies are formed as ordered structure of carbon threads (carbon fiber bundles) in the form of sheets of carbon fiber prepreg produced by parallel packing of threads or carbon fabrics produced by weaving carbon threads. The sheets or wefts are impregnated with resin. Mechanical properties of CFRC materials are distinct from properties of the components - matrix and carbon fiber, and are prescribed by material structure. Diverse versions of reinforcing fiber ordering result in variations of mechanical properties in a wide range. By significant anisotropy of carbon fibers and big difference in elastic characteristics of isotropic resin and anisotropic fibers CFRC laminates possess high elastic anisotropy. Anisotropy depends on carbon fiber orientation, kinds of packing carbon bundles within each ply, fashion of ply stacking in laminate structure - due to type and mutual orientation of comprising plies.
Promotion of fiber-reinforced composites has opened a way to theoretical design of construction materials with prescribed properties. Studies in mechanics of composite materials -establishing principles of generation of elastic and strength properties by means of controlled ordering of reinforcing fibers; finding interrelation between properties of structural units, their arrangement and mechanical properties of an entire composite, studying disruption and flaw generation should be based on efficient methods of mechanical measuring and bulk structure investigation. Plentiful fields of practical application demand for efficient methods of non-destructive evaluation of CFRC laminate microstructure and properties, methods of high resolution flaw detection to reveal small-sized defects in the body of a material or article.
There is a wide set of research methods to study structure and properties at the face of CFRC laminate specimens - light microscopy, electron and probe microscopy, X-ray imaging technique, etc. But these methods are non-effective for studying bulk microstructure within the specimen body, which is fundamental for reinforced materials. Spatial arrangement of structural elements -carbon fiber, fiber bundles, threads and thread tapes; can be distinct within different layers in a ply stack. Occurrence of interlamina adhesive layers, resin pockets and headen flaws - interlamina defoliation, voids, microcracks; are typical for CFRC laminates. Ultrasonic techniques are a powerful instrument for structural feature investigation in CFRC materials and for quantitative characterization oft heir e lastic p roperties. U ltrasound p enetrates f airly deep i nside t he C FRC laminate body. Reflected or transmitted radiation can be employed for measuring velocities of
ultrasound probe beam and usually with high aperture for studying and imaging of surface microstructure, surface elastic properties, surface defects, etc., through time-resolved and continuous-wave regime acoustic microscope techniques. Contrast in acoustic images corresponds to output of transducer. The output signal is stemmed from the elastic responses of materials to acoustic waves - scattering of Rayleigh wave on their surfaces and the nearest sub-surfaces. Thus classical acoustic microscopy with high aperture and ultra-high frequency is suitable to imaging of object surface.
To measure local elastic properties and characterize bulk microstructure of CFRC materials and their structural elements as well as small-sized defects by means of time-resolved pulse micro-acoustic technique, the acoustic probing pulse must be very short, and a low-aperture and reasonable high ultrasonic frequency should be taken into account according to the analysis of previous section. For 50 MHz frequency as an example, when selecting 9M =11”, then we have ft ~ 100jjm, fw ~ 3mm. A high spatial resolution and reasonable penetration depth can be reached by this system. In this case, longitudinal and transverse waves (L, T, LT modes) can be excited and received by the focusing system, as the schematic illustration shown in figure 2-8. Echo signals from ultrasonic reflections on object faces, internal structure elements and defects in the object body make it possible to: 1) measure local bulk elastic properties of CFRC materials and their structural elements; 2) image bulk microstructure and small-sized defects in CFRC materials.
Figure 2-8. Schematic illustration of refraction and reflection of convergent beam in fluid/solid interface in the case of low-aperture. L - longitudinal wave, T - transverse wave, LT - longitudinal-transverse conversion wave.
Contrast in acoustic imaging is formed by output signals of acoustic focusing system. Ultrasonic reflections at CFRC laminate body provide sources of acoustic contrast. Giving