The influence of cyclic creep accumulation rate on the damage evolution of MDYB‐3 polymethyl methacrylate (PMMA) was experimentally investigated. Fatigue tests were carried out at four stress levels by stress control mode. The steady cyclic creep accumulation stage was observed occupying a substantial proportion of all specimens fatigue processes. Cyclic creep strain growth speed and relaxed modulus degradation rate were deduced as two important indicators for describing the damage evolution characteristics. Linear evolution relations of cyclic creep strain and modulus degradation with cycle times were retrieved from different terms of hysteresis loops. A preliminary model was proposed to be able to estimate the damage extent at different cyclic stress levels. The life predictions by the proposed model were compared with the experiment results and the classical power S–N model, which were demonstrated as a good estimation for the fatigue life. It is feasible to make durability evaluations by the characteristics of steady cyclic creep for multiaxis directed PMMA material.
The successive approximation register-analog to digital converter (SAR-ADC) is widely used in the CdZnTe-based gamma-ray imager because of its outstanding characteristics of low power consumption, relatively high resolution, and small die size. This study proposes a digital bit-by-bit calibration method using an input ramp signal to further improve the conversion precision and power consumption of an SAR-ADC. The proposed method is based on the sub-radix-2 redundant architecture and the perturbation technique. The proposed calibration algorithm is simpler, more stable, and faster than traditional approaches. The prototype chip of the 12-bit, 1 MS/s radiation-hardened SAR-ADC has been designed and fabricated using the TSMC 0.35 µm 2P4M CMOS process. This SAR-ADC consumes 3 mW power and occupies a core area of 856 × 802µm 2 . The digital bit-by-bit calibration algorithm is implemented via MATLAB for testing flexibility. The effective number of bits for this digitally calibrated SAR-ADC reaches 11.77 bits. The converter exhibits high conversion precision, low power consumption, and radiation-hardened design. Therefore, this SAR-ADC is suitable for multi-channel gamma-ray imager applications.
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