CRACK TESTING FOR BRAZED ALUMINIUM ALLOYS SPECIMENS

Transcription

1 CRACK TESTING FOR BRAZED ALUMINIUM ALLOYS SPECIMENS Dr.ing.Andrei DIMITRESCU Universitatea Politehnica Bucuresti, Facultatea IMST, Departamentul T.M.R. Dr.ing.Dan NITOI Universitatea Politehnica Bucuresti, Facultatea IMST, Departamentul T.M.S. Abstract: Since aluminum brazing technology is relatively new compared to other permanent joining technologies, this technological process needs a scientific approach. The scope of this paper is the identification of an optimum technological solution for brazing aluminum alloys using crack tested specimens. Keywords: Aluminium alloy; crack testing; brazing. INTRODUCTION To put in execution this destructive test procedure, I used the Universal Fatigue testing Machine INSTRON 8801 in accordance with the effective standards; the loading speed was 1mm/min, the acting force of the grips represents 10% of the force applied on the specimens. For the registration of the local deformations, it was used an extensometer with 50mm measuring base and was applied on the specimens until the specific deformation reached 3%. Fig.1 Universal Fatigue Testing Machine INSTRON 8801: 1.testing device; 2.control system of pressure and temperature; 3.electric motor; 4.software; 5.transforming data system; 6.P.C. for working. 106

2 Fig.2 Wedge Grips serial number 3520.[1] Instron 8801 servo-hydraulic testing system meets the challenging demands of a varied range of both dynamic static and static testing requirements. The 8801 provides complete testing solutions to satisfy the needs of advanced materials and component testing, and is ideally suited for high- and low-cycle fatigue testing, thermo-mechanical fatigue testing, and fracture mechanics. The compact design of the 8801 frame makes it ideal for installation within any laboratory environment, generally without the need for strengthened floors or raised ceiling heights. The Instron 8801 has advantages comparing to other testing machines: Double-acting servo-hydraulic actuator with force capacity up to ± 100kN; High-stiffness, precision-aligned load frame with twin columns and actuator in lower base; Designed for both dynamic and static testing on a variety of materials and components; Patented Dynacell advanced load cell technology for faster testing and reduction of inertial errors; Compact servo-hydraulic fatigue test system frame requires less than 0,5m 2 ; Designed to be used with the 3520 Series of Hydraulic Power Units; Compatible with a large range of grips, fixtures, chambers, video extensometers, protective shields and other accessories. The Instron 8801 is supplied with a digital 8800 controller that provides full system control including features such as automatic loop tuning, amplitude control, specimen protect, 19-bit resolution across the full range of transducers, and adaptive control technology. It also allows access to WaveMatrix Dynamic Testing Software, Bluehill Software for static tests, and other application specific software, such as the Low Cycle Fatigue or Fracture Mechanics suite.[1] 107

3 EXPERIMENTAL DATA The crack testing of the experimental specimens in case of aluminum brazed alloys were executed on two units of specimens named onwards folded specimens and experimental specimens. The first unit consists on 6 specimens that were brazed using an optimum technology: pickling with Aloclene 100 solution, applying the filler material on both sides of the base material, using spectral acetylene and a neutral flame. It is mentioned that during the entire period of assembling the specimens it was used one single operator to avoid the human errors. The folded specimens were retrieved from the same material as the experimental specimens. The specimens were brazed head to head by folding the ends 5mm long under the terms of SR EN [2] referring to the specimens used for the crack testing (peeling test). It is to be mentioned that the brazing area is constant on all the specimens. Fig.3 Unit of tests on folded specimens. Fig.4 The results of the crack testing on folded specimens. Tab.1 The values maximum tensile stress - load on folded specimens. 108

4 The second unit of specimens used for the crack testing is part of the experimental specimens. Representative technologies were considered those that had very good results on nondestructive examination. Fig.5 Unit of representative experimental specimens. a. 109

5 b. c. Fig.6 Graphic maximum load tensile on experimental specimens. CONCLUSIONS In the case of the folded specimens and the experimental specimens, the crack appears in the base material, not in the brazed joint. In the case of both specimen units, the results dispersal validates the experiments. The technology that consists on pickling with Aloclene 100 solution, applying the filler metal on both sides of the base material, using spectral acetylene and neutral flame can be considered the optimum way because in consequence of the crack testing (peeling testing) could be obtained a maximum resistance in the brazing joint. 110

6 REFERENCES Web-site: - accesată în SR EN 12797:2002, Încercări distructive ale îmbinărilor lipite tare, ASRO, aprilie A.DIMITRESCU, The Distribution of Filler Material on Base Metals During Brazing of Aluminum Alloys, 6rd Symposium Durability and Reliability of Mechanical Systems, Tg. Jiu, A.DIMITRESCU, The Influence of Brazing Temperature on the Metallographic Microstructure of the Bonded Weld, 6rd Symposium Durability and Reliability of Mechanical Systems, Tg. Jiu, A.DIMITRESCU, F.BACIU, The Variation of the Fatigue Curve of Different Surface Preparation Technologies of Aluminum Alloys, 6rd Symposium Durability and Reliability of Mechanical Systems, Tg. Jiu,