Identification of residual stress phenomena based on the hole drilling method in explosively welded steel-titanium composite Aleksander Karolczuk*, Mateusz Kowalski*, Krzysztof Kluger*, Fabian Żok** * Opole University of Technology XII International Symposium on Explosive Production of New Materials: Science, Technology, Business, and Innovations, May 25-30, 2014, Cracow The Project was financed from a Grant by National Science Centre (Decision No. DEC-2011/03/B/ST8/05855) ** Z.T.W Explomet S.J., Opole, Poland

2 The plan of presentation Introduction Experimental research Residual stress calculations Results analysis Summary

3 Introduction 1) Sources of residual stresses Manufacturing process The heat treatment Flattening process 2) Consequences of residual stresses Failure of joining process Material strength under monotonic and fatigue loadings (negative or positive) Stress corrosion cracking (suppressed under compressive stresses) 3) The aim of the paper Determination of the influence of the heat treatment on residual stress state in titanium layer of Steel-Titanium bimetal

4 Experimental research Basic information concerning the analyzed bimetal: Flayer plate: Titanium Grade 1 (6 mm) Basic plate: S355J2+N steel(40 mm) Steel S355J2 Chemical element:CSiMnPSCu Maximum content, % weight:0,220,551,600,025 0,45 Titanium Grade 1 Chemical element:CFeHNOTi Maximum content, % weight:0,100,200,0150,030,1899,5 Table 1. Chemical composition steel S355J2+N (EN :2004) and titanium Grade 1 Material Mechanical properties R eH, MPaR m, MPaE, GPa, - A 5, % , 1/K S355J2+N * * 206 0,27-0, * 13,0  Grade (R p02 ) * * 100 0,37 ** * 8,6  * - manufacturer certificate, ** - own research (titanium after explosive welding Table 2. Mechanical properties of the steel S355J2+N and titanium Grade 1

5 Experimental research Draft of welded plate with ignition point and specimen locations. -3 plates (210 x 180 x 46 mm) without the heat treatment -3 (210 x 180 x 46 mm) plates after the heat treatment The heat treatment: soaking in 600 o C for 90 minutes

6 Experimental research Residual stress measurements were performed using the hole drilling method that consists of strain measurements (relaxation) around the drilled hole

7 Experimental research Diameter: 1.5 mm (drill) Speed : 6000 rpm Two points of measurement for each plate

8 Experimental research Strain history registered in titanium during the drilling process Measured stabilized strain values in titanium layer, registered in three directions: A, B, C

9 Experimental research Influence of the drilling process on the measured strains Titanium plate after the heat treatment:

10 Residual stress calculations Residual stress calculations were performed according to: -The strain gauge manufacturer’s prescriptions (TML) -The ASTM (E837-08) prescriptions (ASTM) TMLASTM Single hole depth equal to 1.2 of hole diameter Takes into account the strain measured for several hole depths (more accurate) Assumptions: -Uniform stress distribution – averaged residual stress state -Plane stress state -Isotropic materials

11 Residual stress calculations Plate Point 1Point 2 11 22 (1)(1)  (P) 11 22 (1)(1) I II IV Example results: TML - the specimens without the heat treatment. Where:  (  1 ) - angle measured clockwise from direction A to  1 ;  (P) - angle measured clockwise to A direction from detonation direction.

12 Result analysis The mean values of the principal stress σ 1, σ 2 and standard deviations calculated according to the TML and ASTM prescriptions for the specimens without and after the heat treatment.

13 Result analysis Maximum principal stress direction and direction of detonation ? Directions of the maximum principal stresses related to detonation directions. Calculations according to the TML and ASTM methods.

14 Result analysis 1) The tensile stresses in the titanium layer – introduced during explosive welding process 2) Compressive stresses in the titanium layer - appearing after the heat treatment are the result of different thermal expansion coefficients of welded materials

15 Summary 1) The heat treatment changes the residual stress state in titanium. The stress state in specimen without the heat treatment is tensile and after the heat treatment is compression. 2) Direction of the maximum principal stress does not coincide with direction of detonation wave. 3) Calculation shows inhomogeneous residual stress state. The stresses change depending on the hole depth.