Study of Ultrasound C-Scan Sensitivity in Analyzing Heat Damages on a CFRP Panel

Transcription

1 Study of Ultrasound C-Scan Sensitivity in Analyzing Heat Damages on a CFRP Panel 6 Th International NDT Conference November 2014 Madrid, Spain A S W I N H A R I D A S 1, B. S T E P H E N W O N G 2 1 M E C H A N I C A L A N D A E R O S P A C E E N G I N E E R I N G, G E R M A N I N S T I T U T E O F S C I E N C E A N D T E C H N O L O G Y, S I N G A P O R E ; P H O N E : ; E - M A I L : A S W I N. H A R I D A T U M. D E 2 S C H O O L O F M E C H A N I C A L A N D A E R O S P A C E E N G I N E E R I N G, N A N Y A N G T E C H N O L O G I C A L U N I V E R S I T Y, S I N G A P O R E , T E L : , F A X : , E - M A I L : M B W O N N T U. E D U. S G 6th International Symposium on NDT in Aerospace, 12-14th November 2014, Madrid, Spain -

2 Introduction Aircraft Fire Causes: Lightning Engine Fires Electrical Systems Weapon Systems etc Source: pdf

3 Use of Composites In Aircrafts IFTC (International Fire Training Center) UK: Training Notes Source: In 2003, the IFTC, at Teeside in the UK, Training Notes Source: pdf Conclusion From Research: Thus a potential requirement to understand behavior of composites at Varying temperature to see damage initiation and certify the extent of damage.

4 Our Contribution Understanding the physical behaviors of composites in case of low temperature heating. a) Temperature ranges C. b) Time range for heating min. Experimental analysis of the heated specimen using Ultrasound C-Scan to understand its sensitivity in damage detection a) Understanding the potential areas to C-Scan. b) Understanding the extent of damage from the C-Scans and the corresponding A-Scans. Future Work (Being Carried out at NTU Singapore) a) Correlation of the C-Scan results with the results obtained from thermography of the affected areas. b) Evaluating the attenuation of sound in the damaged areas to create a reference for future damage analysis.

5 Pre-Test Preparations The specimen was divided into smaller squares mostly 4X4mm 2 and few 6X4mm 2 After each square where heat damage was to be imposed 4mm was left free so that no two damages interacts. As long exposures to the fumes from the CFRP Sheet to cause health issues masks were used for protection from the fumes. Gloves were used to protect from the hot specimen after tests. Experiments were done outside considering all safety requirements.

6 Imposing Heat damage (Up) Experimental setup for imposing heat damages (Right) Experimental Algorithm.

7 Observations during Experimentation Factors affecting the experiments: Tropical climate conditions in Singapore. Distance of the Heat Gun from the specimen surface (Here considered :2mm) Types of nozzle: Normal nozzle diameter: 40mm Reducer Nozzle diameter: 5mm Fumes were observed on the opposite side of heating showing that the heating has completely passed through

8 C-Scan Damage Detection (Up) Experimental setup for C-Scan Robot (Right) Experimental Algorithm for C-Scan.

9 Results From the C-Scan Point 1- A-Scan. Soundwaves pass through the entire thickness and backscatters. Point 2- A-Scan. Soundwaves do not penitrate the entire thickness and bounces back mostly at 1mm depth (0.5x total depth) Point 3- A-Scan. Soundwaves do not penitrate the entire thickness and bounces back at approx. 0.2mm- 0.4mm depth. Two different defects noticed. 1. Defects at 1mm (Half the specimen thickness) 2. Defects at 0.4mm (Near surface defects) Defects at 0.4mm Defect at 1mm Total thickness: 2mm Defects at 0.4mm

10 Sizing of the damages CFRP SHEET C-SCAN (INVERTED) CFRP SHEET C-SCAN IMAGE Top Left: Sizing comparison for defect C, 15min, Side 1 of scan. Top Right: Sizing comparison for defect C, 15min, Side 2 of scan. Measuring Section Length Measured C-Scan Length Measured on the CFRP Specimen 39mm Diameter of Nozzle C-15min 37mm (Front) 40mm C-15min (Back) 37mm 37mm 0% C-Scan Error From Visual 5.1% Thus damage size correlation is done effectively using the C-Scan Side 1: Top Surface where heat load was applied Side 2: Bottom Surface

11 Results From the C-Scan Top and bottom near surface damage caused due to weak epoxy layer : Woven Layer. The middle layer acts as a neutral plane and due to the fumes moving to the top and the bottom possible delamination observed in the middle layer.

12 Reducer Nozzle The reducer nozzle used together with the heat gun had a 30 degree bend causing heat losses. External burns were noted the size of the nozzle itself (5mm) No internal damages noted in the areas where the reducer nozzle was used possibly because of heat losses in the bends. Cross Checks were done through thermography to note that no internal damages were registered. C-Scan Sensitivity complimented.

13 Conclusions The C-Scan was able to identify the various damages caused by heating namely the near surface damages and the internal damages. Damage sizing could be done effectively and near comparisons could be made with visual damages. No internal damage conditions observed for the reducer nozzle was verified using the thermography procedure. Steps of verification with Thermography is currently being carried out in NTU Singapore. Main Conclusion: Procedures for Ultrasounds could be developed for damage analysis of heat damaged composite specimens with good accuracy.