In-situ measurements of deformation to fatigue failure on a flat-type divertor mockup under high heat flux loads by 3D digital image correlation

Abstract

Plasma-facing components (PFCs) usually need to withstand extreme incident heat flux conditions in nuclear fusion engineering. In situ measurements of deformation to fatigue failure of PFCs under high heat flux (HHF) tests are significant and essential to understand their thermal-mechanical behaviors under servicing conditions; these measurements can provide first-hand and important information for evaluating and optimizing design performance and manufacturing techniques. However, unlike traditional contact measurements with strain gauges, the contactless optical measurement technique is rarely applied to measure or monitor the deformation to fatigue damage process of PFCs employed in HHF tests. In this work, a comprehensive HHF experimental platform was established by combining an electron gun scanning HHF heating system with a three-dimensional digital image correlation (3D-DIC) measurement system based on a vacuum chamber and specially designed optical windows and light sources. The 3D-DIC technology was utilized to measure the field deformation of a divertor mockup under cyclic HHF loads. Validation and qualification tests were conducted on the comprehensive experimental platform to ensure the performance of the platform and the accuracy of the 3D-DIC method. The thermal-induced field deformation of a flat-type divertor mockup under the conditions of 1000 HHF cycles at 10 MW m−2 and 300 HHF cycles at 20 MW m−2 using the 3D-DIC technique was then measured. The mechanical behavior of the accumulated plastic strain and fatigue debonding failure of the W/Cu interface due to periodic thermal stress were captured in situ by the measured strain curves and contours for the first time during HHF tests. The results demonstrate the feasibility and accuracy of the 3D-DIC technique for in situ fatigue deformation and damage strain measurements of PFCs during HHF tests. The proposed methods and technologies are expected to be applied to measure and monitor the servicing performance of PFCs under servicing conditions.

Lifetime measurement of a particular deep crack failure on a flat-type divertor mockup under cyclic high heat flux loading conditions

“…To study the thermal deformation responses and deep cracking failure process of the flat-type divertor mockup under cyclic HHF loads, a testing case for 1800 cycles of 10 MW m −2 was conducted on a comprehensive HHF experimental platform [21]. This platform mainly consists of a 30 kW electron beam irradiation facility (THDW-30, China) and a DIC measurement system (Nanjing PMLAB Sensor Tech.…”

“…where the γ is determined as 0.5 based on calibration measurements same with those in reference [21], U and I are acceleration voltage and beam current of electron gun, respectively. The scanning frequency, beam current and acceleration voltage of the electron beam heating system were set as 3 kHz, 150 mA and 80 kV, respectively.…”

“…However, the thermomechanical behavior of the PFCs related to fracture damage, such as displacement and strain fields, cannot be recorded or measured directly by IR images, which is very important for cracking failure mechanism evaluation. Recently, Pan et al quantitatively measured the displacement and strain fields of a divertor mockup under long cyclic HHF loading conditions and observed the delamination of a W/Cu interface in situ by digital image correlation (DIC) technology [21]. This proves the feasibility of measuring the deformation and damage process of PFCs under cyclic HHF loads.…”