1. XII International Symposium on Explosive Production of New Materials: Science, Technology, Business, and Innovations, May 25-30, 2014, Cracow
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**
The Project was financed from a Grant by National Science Centre (Decision No. DEC-2011/03/B/ST8/05855)
* Opole University of Technology
** 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)
Table 1. Chemical composition steel S355J2+N (EN :2004) and titanium Grade 1
Steel S355J2
Chemical element: C Si Mn P S Cu
Maximum content, % weight:
0,22
0,55
1,60
0,025
0,45
Titanium Grade 1 Fe H N O Ti
0,10
0,20
0,015
0,03
0,18
99,5
Table 2. Mechanical properties of the steel S355J2+N and titanium Grade 1
Material
Mechanical properties
ReH, MPa
Rm, MPa
E, GPa
, -
A5, %
, 1/K
S355J2+N * *
206
0,27-0,30
24-34*
13,010-6
Grade 1
(Rp02)* *
100
0,37**
43-56*
8,610-6
*- manufacturer certificate , **- own research (titanium after explosive welding

5. Experimental research
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 600oC for 90 minutes
Draft of welded plate with ignition point and specimen locations.

6. Experimental research
Residual stress measurements were performed using the hole drilling method that consists of strain measurements (relaxation) around the drilled hole
Manofacturer: TML TokyoSokkiKenkyujo Co., Ltd.
Type: FRS-2
Dimensions : gauge length: 1.5 mm
width: 1.3 mm
outer diameter:  9.5 mm
Centerline diameter:  5.14 mm
Nominal resistance: 120 ± 0.5 
Gauge factor: 2.0

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)
TML
ASTM
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
Example results:
TML - the specimens without the heat treatment.
Plate
Point 1
Point 2 1 2
(1)
(P) I
235
227
-50
-12
269
213
-34
-20 II
243
210
-35
174
373
339
-125 99 IV
313
248 -2
-100
310
220
-43
-130
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 σ1 , σ2 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.