Evaluation of high-velocity impact welding's interfacial morphology between Cu and CP-Ti using SPH numerical analysis method

SPH 해석기법을 이용한 Cu와 CP-Ti 고속 충돌 접합 단면의 형상학적 평가

Abstract

The existence of different thermodynamic properties results in various undesirable effects, such as thermal deformation and residual stress, in heat-welding processes. The solid-state junction, by using explosive or electromagnetic forces, i.e., high-velocity impact welding without employing heat is advantageous in joining materials with different thermodynamic properties. In the solid-state junction, the joining is performed within a short time, a high velocity and large deformations are accompanied by interfacial surfaces. The numerical analysis models play an important role in the understanding of the mechanism of high-velocity impact welding. However, in the analysis of high velocity and large deformations, the conventional Lagrangian method has low reliability due to the occurrence of entanglements. In this study, high-velocity impact welding between Cu and CP-Ti with different thermodynamic properties was performed using a un-gridded numerical method, SPH (Smoothed Particle Hydrodynamics), and interfacial morphology occurred. As a result of the analysis, the interfacial morphology was confirmed and the compared degree of shape (straight, vortex), period, length, and so on appeared differently depending on the relationship between the parameters (impact angle and speed).

열을 이용한 접합은 소재 간 열역학적 차이에 의한 열 변형 및 잔류응력 등 원하지 않은 결과를 야기한다. 폭발력 또는 전자기력을 이용한 고상 접합은 열이 사용되지 않아 열역학적 차이가 있는 소재접합에 이점이 있다. 이때, 해당 접합은 짧은 시간 내(${\mu}s$) 이루어지며, 접합면에서 고속 및 대 변형이 동반된다. 수치해석 모델은 고속 충돌 접합 메커니즘을 이해하는 데 중요한 역할을 수행한다. 하지만 고속 및 대 변형이 나타나는 해석에서 전통적인 라그랑지안 기법은 격자 얽힘이 발생해 결과의 신뢰성이 낮다. 본 연구는 무격자 수치해석 방식의 SPH(Smoothed Particle Hydrodynamics)를 이용하여 열역학적 차이가 있는 Cu와 CP-Ti의 고속 충돌 접합을 수행하였고 경계면 결합 형상이 발생함을 확인하였다. 해석의 결과로 경계면 결합 형상이 매개변수(충돌 속도, 충돌 각도)의 관계에 따라 형상의 정도(직선, 소용돌이), 주기, 길이 등이 다르게 나타나는 것을 확인 및 비교하였다.

Fig. 1 High-velocity impact welding experimental setup with stand-off block

Fig. 2 Types of interfacial morphology in impact welding, between nickel and steel(grade 1008), (a) a straight interfacial morphology, (b) wave interfacial morphology, (c) wave with vortices interfacial morphology

Fig. 3 Numerical analysis 2D-model with flyer and base plates.

Fig. 4 Interfacial morphology between flyer and base plate. (a) ~ (c) is results from impact velocity υ=200m/s and impact angle β=10º, 15º, 20º, (d) ~ (f) is results from impact velocity υ=400m/s and impact angle β=10º, 15º, 20º, (g) ~ (i) is results from impact velocity υ=600m/s and impact angle β=10º, 15º, 20º

Fig. 5 Measurements of interfacial morphology ,include wave-height(H), period(λ), and ,length(L).

Fig. 7 At time 5μs, (a) is result from impact velocity 400m/s, avg. welding velocity V is 1.6km/s, and impact angle 15º. (b) is result from impact velocity 400m/s, agv. welding velocity V is 1.2km/s, and impact angle 20º.

Fig. 8 At time 3μs, (a) is result from impact velocity 600m/s, avg. welding velocity V is 2.5km/s, and impact angle 15º. (b) is result from impact velocity 600m/s, avg. welding velocity V is 1.9km/s, and impact angle 20º.

Fig. 9 Resultant velocity of jet phenomenon ((a) is 10º, (b) is 15º, (c) is 20º).

Fig. 6 Interfacial morphology increasing its size according to y direction results from impact velocity 600m/s and impact angle 20º

Table. 1 Material properties used in numerical simulation by SPH analysis[2, 11]

Table. 2 Results of wave-period(λ) from analysis except 200m/s cases.

Table. 3 Results of wave-height(H) from analysis except 200m/s cases.

Table. 4 Results of wave-length(L) from analysis except 200m/s cases.