Tomio Sanda

Detection of impact damage of stiffened composite panels using embedded small-diameter optical fibers

It is well known that barely visible damage is often induced in composite structures subjected to out-of-plane impact, and the mechanical properties of the composites degrade markedly. The stiffened composite panels which are the representative structural elements of airplanes are characterized by impact damage different from that of coupon-level specimens. Therefore, the objective of this study is to apply small-diameter optical fiber sensors to stiffened composite panels for the detection of impact damage. In this study, both multi-mode optical fibers and fiber Bragg grating (FBG) sensors are used for detecting impact load and impact damage in stiffened composite panels. The fibers have polyimide coating with 40 µm cladding diameter which has no serious effect on the mechanical properties of composites. Impact tests are performed using stiffened composite panels with embedded optical fibers. The characteristics of impact damage are investigated. The impact load, the strain and the optical responses of the optical fibers are measured as a function of time. And we discuss the relationships among the optical responses, the impact load and the impact damage.

Effect of Isothermal Aging on Ultimate Strength of High-Temperature Composite Materials for SST Structures

The objective of this experimental study was to evaluate the effect of iso-thermal aging on the ultimate strength of three kinds of carbon/high-temperature composite materials, i.e., G40-800/5260 and MR50K/MR2000N bismaleimide composites and T800H/PI-SP amorphous thermoplastic polyimide composite. These materials are current candidate structural materials for a supersonic transport of the next-generation. The hole-notched and unnotched panels, before being machined to specimens, were isothermally aged at 120°C and 180°C for up to 15,000 hours. Static tests at room and elevated temperatures before and after thermal aging provided the open-hole tensile, open-hole compressive, and short beam shear strengths. Moreover, the effects of five oxidation resistant treatments on open-hole compressive strength at 180°C were investigated after isothermal aging of 5,000 hours at 180°C. The test results clarified the effects of isothermal aging on ultimate strengths and oxidation resistant treatments on open-hole compressive strength. Moreover, the possibility of developing an accelerated aging test method is discussed using a modified Larson-Miller type equation.

Sound and vibration control tests of composite panel using piezoelectric sensors and actuators

We are carried out the tests for the sound and vibration control of the CFRP square panel. 500Hz bandwidth noise through two speakers is applied to the CFRP panel. Our objects are to improve the structural damping of the panel and attenuate the sound power radiated from the panel using piezoelectric sensors and actuators. The dimensions of the CFRP plate are 600.0 mm x 600.0mm in area and 1.8mmt in thickness. Eighteen piezoelectric elements (40.0 x 20.0 x 0.3mmt) are bonded on the surface of the panel by epoxy adhesive. The panel is driven using some piezoelectric elements as actuators. The vibration of the panel is monitored using piezoelectric elements as sensors. We can get the strain of the panel from the voltage induced by piezoelectric elements. The signals are sent to digital signal processor (DSP) through filters and the control signal are sent to the power amplifiers. The amplified signals drive the piezoelectric actuators. The vibration and the radiated sound power of the panel are suppressed. We try to apply two methods for the control which are the gain control and the reduced LQG control. In the case of the gain control, the strain is reduced as much as 10-20 dB at some resonant peaks and the radiated sound pressure level as much as 1-15 dB. The radiated sound power is reduced by 1.59dB in the 0-500Hz frequency range. In the case of the LQG control, the strain is reduced as much as 7-10dB at some resonant peaks and the radiated sound pressure level as much as 1-7dB. The radiated sound power is reduced by 0.7dB in the 0-500Hz frequency range.

Real-time detection of impact load on composite laminates with embedded small-diameter optical fiber

It is well known that the compression after impact (CAI) strength of carbon fiber reinforced plastic (CFRP) laminates decreases by impact damage, especially delamination. The impact damage has a close relation to impact energy, which can be derived from the time history of impact load. Thus, it is important to detect the impact load applied to the composites. In this study, single-mode or multi-mode small-diameter optical fibers embedded in CFRP laminates were used as a sensor for detecting the impact load. Diameters of the cladding and the polyimide coating are 40 μm and 52 μm, respectively. Such optical fibers embedded inside laminas cause no serious effect on the mechanical properties of composites. The optical fiber sensors were able to detect the impact by bending loss in the vicinity of impact point. The optical fibers were embedded parallel to reinforcing fibers in CFRP composites. Charpy impact tests were performed for the CFRP specimens. The strain on the surface of the specimens, the optical loss and the impact load were measured as a function of time. Then, the relationship between the optical loss and the impact load was discussed experimentally and theoretically.

Noise and vibration reduction technology in aircraft internal cabin

The study to reduce noise and vibration in aircraft cabin through PZT was implemented, using a semi-monocoque structure, 1.5m in diameter and 3.0m long with 2.3mm skin, which stimulates an aircraft body. We utilized PZT of 480 pieces bonded on inner surface of the structure as sensor and actuator. We applied random noise of low frequency range between 0~500Hz to the test model. We tried to reduce the vibration level of structure and internal air due to the external load by controlling the PZTs. Two control methods, gain control and feed-forward control, were tried. We measured internal sound pressure on 150 spots and compared overall values of sound pressure with gain control to them without control and evaluated its reduction capability. The tests showed 4.0dB O.A. reduction at maximum in gain control and 3.5dB O.A. reduction at maximum in feed forward control.

Noise and vibration reduction technology in aircraft cabins

This study investigates how to reduce noise and vibration in aircraft cabins with Pb(TiZr)O3 (PZT), using a semi-monocoque structure 1.5 m in diameter and 3.0 m long with a 2.3 mm skin, which simulates an aircraft body. We utilized 480 pieces of PZT bonded on the inner surface of the structure as sensors and actuators. We applied random noise in the low frequency range from 0 to 500 Hz to the test model. By controlling the PZTs, we tried to reduce the vibration level of the structure and the internal air due to the external load. Two control methods, gain control and feed-forward control, were tried. We measured internal sound pressure at 150 points and compared the overall values of sound pressure with gain control to those without control and evaluated the reduction capabilities. The tests demonstrated a maximum 4.0 dB O.A. reduction with gain control and a maximum 3.5 dB O.A. reduction with feed-forward control.

Impact damage detection system using small-diameter optical fiber sensors wavily embedded in CFRP laminate structures

It is well known that barely visible damage is often induced in composite structures subjected to out-of plane impact, and the mechanical properties of the composites decrease markedly. In this study, some element technologies for the detection of the damage are explained. Those are (1) the technologies for the arrangement of embedded small-diameter optical fibers which have no serious effect on the mechanical properties of composites, (2) the technologies for the egress of the optical fibers using “the embedded connector for smart structures” which can be trimmed without care about the optical fibers, (3) the technologies for the damage detection system that has the functions for data acquisition and analysis, the evaluation of the initiation and the position of damage, and the visualization of damage information. The impact test using the composite airframe demonstrator is conducted. The sensors embedded in the upper panel of the stiffened cylindrical composite structure with 1.5 m in diameter and 3 m in length, are FBG sensors for strain measurement and the optical fibers for optical loss measurement. The detection of damage in the composite structures using a developed damage detection system is demonstrated.

Impact damage detection of curved stiffened composite panels by using wavy embedded small-diameter optical fibers

It is well known that barely visible damage is often induced in composite structures subjected to our-of-plane impact, and the mechanical properties of the composites decrease markedly. So far, for the significance of the damage monitoring, the impact test of the CFRP laminate plates with embedded small-diameter optical fibers were conducted, and it was found possible to detect impact load and impact damage in real-time by measuring the optical loss and strain response. But the stiffened composite panels, which are the representative structural elements of airplane. Are characterized by different impact damage from that of the composite plates. In this study, single-mode and multi-mode optical fibers are used as a sensor for detecting impact load and impact damage in curved/stiffened composite panels. Those fibers have polyimide coating and about 40 micron in diameter which will have no serious effect on the mechanical properties of composites. Impact test are performed using the panels with wavy embedded optical fibers. The characteristics of impact damage are investigated. The impact load, the strain measured by FBG sensors and the optical intensity of the optical fibers embedded in the composites are monitored as a function of time. And we discuss the relationship between optical response, impact load and impact damage.

Impact damage detection of stiffened composite panels by using embedded small-diameter optical fibers

It is well known that barely visible damage is often induced in composite structures subjected to out-of plane impact, and the mechanical properties of the composites decrease markedly. The stiffened composite panels, which are the representative structural elements of airplane, are characterized by different impact damage from that of the coupon level specimens. Therefore, the goal of this study is that small-diameter optical fiber sensors are applied in stiffened composite panels, and it is discussed about the possibility of the detection of impact damage in the structures by the sensors. In this study, both multi-mode optical fibers and fiber bragg grating (FBG) sensors are used for detecting impact load and impact damage in stiffened composite panels. The fibers have polyimide coating and about 40 micrometers in cladding diameter which will have no serious effect on mechanical properties of composites. Impact tests are performed using the stiffened composite panels with embedded optical fibers. The characteristics of impact damage are investigated. The impact load, the strain and the optical responses of the optical fibers are measured as a function of time. And we discuss the relationship among the optical responses, the impact load and the impact damage.

Flutter and vibration control of an aluminum plate wing by piezoceramic actuators

We carried out tests and analysis of flutter and vibration control of rectangular aluminum plate wing. The dimensions of the plate wing (420.0 X 140.0 X 1.0 mmt) were determined based on the wind tunnel size and blowing air velocity. The plate wing was driven by eight piezoceramic actuators bonded on the surfaces at the wing root part. Acceleration sensor was located at the wing tip and the signal was sent to digital signal processor through filters and control signal was sent to power amplifier. Amplified signal drove the piezoceramic actuator and suppressed vibration of the plate wing. System consist of structure, piezoceramic actuator and unsteady aerodynamic force was modeled into the standard form of modern control theory. Piezoceramic actuators force was modeled using analogy of thermal analysis. Unsteady aerodynamic force in case of flutter control was calculated by DLM (frequency domain), then transformed to Rogers approximation for the purpose of time domain analysis. Full order control law consist of optimum regulator and Kalmans filter was reduced to low order law for practical use. First, we carried out the test for vibration control. In this case, structural damping ratio of the system increased remarkably in both case of gain control and reduced LQG control. Using gain control, that of the system increased up to 0.3. Second, we carried out the wind tunnel test of flutter control. Flutter speed at test increased about 2.9 m/s (10.8%, in calculation 12.2%) using reduced LQG controller.