Analysis on deformation characteristics and energy dissipation of marble under different unloading rates

Ispitivanja oštećenja provodila su se na mramoru kod različitih brzina ograničenja tlaka pri rasterećenju da bi se dobila krivulja promjene energije cijeloga procesa deformacije i oštećenja. S povećanjem brzine rasterećenja, razlike vršnog naprezanja kod oštećenja mramora su se smanjile, razlike ograničenja tlaka su se povećale, omjeri prirasta ograničenja tlaka kod svakog naprezanja su bili manji, a deformacija volumena je bila osjetljivija na promjene ograničenja tlaka kod rasterećenja. Oštećenje kod rasterećenja nastalo je širenjem volumena, i što je veća bila brzina rasterećenja, lakše je dolazilo do oštećenja stijene. S porastom brzine rasterećenja, prirast ukupne apsorbirane energije, prirast elastične energije i prirast disipacije energije smanjili su se u stadiju rasterećenja mramora. Prirast rasipanja energije u postupku rasterećenja bio je pet puta veći od onoga u postupku opterećenja dok je prirast elastične energije pokrivao svega 10 % ukupne akumulirane energije. Postupak rasterećenja pokazao je porast rasipanja energije, a stanje geo-naprezanja stijenske mase odredilo je nivo energije otpuštene u oštećenju.Failure tests were conducted on marble under different unloading confining pressure rates to obtain the energy change curve of whole-process deformation and failure. With increasing unloading rate, the peak stress differences in marble failure were reduced, confining pressure differences in failure increased, the increment ratios of each stress confining pressure were smaller, and the volume deformation was more sensitive to changes in unloading confining pressure. Unloading failure was caused by volume expansion, and the greater the unloading rate was, the easier the rock failure was. With the increasing unloading rate, total absorbed energy increment, elastic energy increment and dissipated energy increment were reduced in the unloading stage of marble. The dissipated energy increment in the unloading process was more than five times that in the loading process, while the elastic energy increment only accounted for 10 % of total stored energy. The unloading process showed increasing dissipated energy, and the geo-stress state of the engineering rock mass determined the level of energy released in failure

Mixed Fault Tolerance Protocols with Trusted Execution Environment

Blockchain systems are designed, built and operated in the presence of failures. There are two dominant failure models, namely crash fault and Byzantine fault. Byzantine fault tolerance (BFT) protocols offer stronger security guarantees, and thus are widely used in blockchain systems. However, their security guarantees come at a dear cost to their performance and scalability. Several works have improved BFT protocols, and Trusted Execution Environment (TEE) has been shown to be an effective solution. However, existing such works typically assume that each participating node is equipped with TEE. For blockchain systems wherein participants typically have different hardware configurations, i.e., some nodes feature TEE while others do not, existing TEE-based BFT protocols are not applicable. This work studies the setting wherein not all participating nodes feature TEE, under which we propose a new fault model called mixed fault. We explore a new approach to designing efficient distributed fault-tolerant protocols under the mixed fault model. In general, mixed fault tolerance (MFT) protocols assume a network of $n$ nodes, among which up to $f = \frac{n-2}{3}$ can be subject to mixed faults. We identify two key principles for designing efficient MFT protocols, namely, (i) prioritizing non-equivocating nodes in leading the protocol, and (ii) advocating the use of public-key cryptographic primitives that allow authenticated messages to be aggregated. We showcase these design principles by prescribing an MFT protocol, namely MRaft. We implemented a prototype of MRaft using Intel SGX, integrated it into the CCF blockchain framework, conducted experiments, and showed that MFT protocols can obtain the same security guarantees as their BFT counterparts while still providing better performance (both transaction throughput and latency) and scalability.Comment: 12 pages, 3 figure