Da-Ming Chen

Delamination Identification of Laminated Composite Plates Using a Continuously Scanning Laser Doppler Vibrometer System

Delamination frequently occurs in a laminated composite structure and can cause prominent local anomalies in curvature vibration shapes associated with vibration shapes of the composite structure. Spatially dense vibration shapes of a structure can be rapidly obtained by use of a continuously scanning laser Doppler vibrometer (CSLDV) system, which sweeps its laser spot over a vibrating surface of the structure. This paper extends two damage identification methods for beams to identify delamination in laminated composite plates using a CSLDV system. One method is based on the technique that a curvature vibration shape from a polynomial that fits a vibration shape of a damaged beam can well approximate an associated curvature vibration shape of an undamaged beam and local anomalies caused by structural damage can be identified by comparing the two curvature vibration shapes, and the other is based on the technique that a continuous wavelet transform can directly identify local anomalies in a curvature vibration shape caused by structural damage. In an experimental investigation, delamination identification results from the two methods were compared with that from a C-scan image of a composite plate with delamination.

Damage Identification of Plates by using a Continuously Scanning Laser Doppler Vibrometer System

A damage identification method for plates by using a continuously scanning laser Doppler vibrometer (CSLDV) system is presented. A new uniform-speed scan algorithm is proposed to create a two-dimensional scan trajectory and automatically scan a whole plate surface. Based on the new scan algorithm, the demodulation method is extended from one dimension for beams to two dimensions for plates to obtain a full-field operating deflection shape (ODS) of the plate from velocity response. The full-field ODS of an associated undamaged plate is obtained by using polynomials to fit the corresponding full-field ODS from the demodulation method. A curvature damage index (CDI) using differences between curvatures of ODSs associated with ODSs that are obtained by the demodulation method and the polynomial fit is proposed to identify damage. An experiment of an aluminum plate with damage in the form of 10.5% thickness reduction in a damage area of 0.86% of the whole plate scan surface area is conducted to investigate the proposed method. The damage can be successfully identified near an area with high values of a CDI

Investigation of Notch-Type Damage Identification by Using a Continuously Scanning Laser Doppler Vibrometer System

This paper experimentally investigates a notch-type damage identification methodology for beams by using a continuously scanning laser Doppler vibrometer (CSLDV) system. The velocity response of a beam along a scan line under sinusoidal excitation is measured by the CSLDV system and a corresponding operating deflection shape (ODS) of the beam is obtained by the demodulation method. The ODS of the associated undamaged beam is obtained by using a polynomial with a proper order to fit the corresponding ODS from the demodulation method. The curvature of an ODS (CODS) can be calculated with a high quality due to a dense measurement grid of the ODS. A curvature damage index (CDI) is proposed to identify a notch with a length of 1 mm along a beam and a depth of 0.9 mm under different sinusoidal excitation frequencies. The CDI uses the difference between CODSs associated with ODSs that are obtained by the demodulation method and the polynomial fit. The notch is successfully identified near regions with high values of CDIs at different excitation frequencies.

Structural Damage Identification Using Free Response Measured by a Continuously Scanning Laser Doppler Vibrometer System

Spatially dense operating deflection shapes and mode shapes can be rapidly obtained by use of a continuously scanning laser Doppler vibrometer (CSLDV) system, which sweeps its laser spot over a vibrating structure surface. This paper introduces a new type of vibration shapes called a free response shape (FRS) that can be obtained by use of a CSLDV system, and a new damage identification methodology using FRSs is developed for beam structures. An analytical expression of FRSs of a damped beam structure is derived, and FRSs from the analytical expression compare well with those from a finite element model. In the damage identification methodology, a free-response damage index (FRDI) is proposed, and damage regions can be identified near neighborhoods with consistently high values of FRDIs associated with different modes. The proposed methodology was numerically applied to identify damage in a beam structure.

Damage Identification Using a Continuously Scanning Laser Doppler Vibrometer System

A continuously scanning laser Doppler vibrometer (CSLDV) system is capable of rapidly obtaining spatially dense operating deflection shapes (ODSs) by continuously sweeping a laser spot from the system over a structure surface. This paper presents a new damage identification methodology for beams that uses their ODSs under sinusoidal excitation obtained by a CSLDV system, where baseline information of associated undamaged beams is not needed. A curvature damage index (CDI) is proposed to identify damage near a region with high values of the CDI at an excitation frequency. The CDI uses the difference between curvatures of ODSs associated with ODSs that are obtained by two different CSLDV measurement methods, i.e., demodulation and polynomial methods; the former provides rapid and spatially dense ODSs of beams, and the latter provides ODSs that can be considered as those of associated undamaged beams. Phase variables are introduced to the two methods for damage identification purposes. The proposed damage identification methodology was experimentally validated on a beam with damage in the form of machined thickness reduction. The damage and its region were successfully identified in neighborhoods of prominent peaks of CDIs at different excitation frequencies.Copyright