| Fiber-reinforced composite structures have the advantages of lightweight,high specific strength,high specific modulus and strong design-ability,which are widely used in aviation,aerospace and other engineering fields.As the fiber-reinforced composite structure is prone to manufacturing defects,and its service environment is complex,long-term in high temperature,high pressure,high amplitude vibration,corrosion,impact and other harsh conditions,it is very likely that fiber fracture,matrix crack,debonding,fatigue,layered damage occur.However,the damage detection of composite material structure is difficult due to the anisotropy of materials,the conductivity of carbon fibers,acoustic attenuation,and many injuries often occur underneath the surface,making it different from traditional metal materials in nondestructive testing.Therefore,the damage detection of composite material structures is more difficult than that of metal structures.In this paper,the fiber reinforced composite beam and plate structure are studied,and a two-dimensional laser scanning vibration measurement system for high temperature vibration measurement is built.The damage location method and damage evolution rule of this type of composite beam and plate structure at room temperature are studied in depth.The specific research content can be divided into the following parts:(1)A two-dimensional laser scanning vibration testing device for high temperature vibration measurement was designed and developed.Firstly,the hardware configuration of the device,the selection of the scanning mode,the selection of the scanning direction,the setting of scanning coordinate origin,the display of current position,the setting of motion tracking,the control method of scanning speed and the principle of acquisition of mode shape are introduced in detail.Then,HF10 carbon fiber/resin composite plate was taken as the research object.The vibration testing system of composite material plates under cantilever boundary condition was built,and a set of standard testing process was summarized.Finally,in order to study the influence of different tightening torques on the natural frequency under cantilever boundary conditions and the influence of thermal environment on the mode shape of composite plates,the frequency sweep and fixed frequency tests are carried out under normal temperature and thermal environment,respectively.(2)A damage locating method based on the power exponential approximation-lumped mass approach is proposed to accurately identify the damage location of fiber-reinforced composite beam and plate structures.Firstly,taking the composite beam and plate structure of this type as an example,the corresponding concentrated mass models are established.By combining theory with experiment,the residual force vector after damage is obtained,and the maximum value of residual force element is taken as the key location index of damage.Then,the criterion of damage approximation is proposed,the damage location theory principle is clarified,and a set of standard positioning process is summarized.Finally,the proposed method is utilized to study the damage locations of T300 carbon fiber/resin-based composite beams and plates with different fiber fracture damage.It is found that the proposed method can effectively identify the damage location of composite beam and plate structures.(3)A damage locating method and a damage evolution hypothesis for fiber-reinforced composite plates with damaged in thermal environments considering the influence of temperature were proposed.Firstly,a lumped mass model of fiber-reinforced composite plate structures in thermal environment was established.Besides,the damage locating method of composite plates proposed in Chapter 3 was combined to further propose the damage evolution degree and damage evolution area rule hypothesis of composite plates under thermal environment.Then,the fiber-reinforced composite plate under cantilever boundary condition was taken as research object to study the damage evolution degree and damage evolution area law under different heating time at temperature T,and the damage evolution degree and damage evolution area function were obtained.Finally,the validity of the damage evolution degree function and damage evolution area function were verified by comparing the theoretical results with the experimental results. |
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