Transient Stress Research Articles

Transient fault creep on the Xidatan (Tibet) fault driven by viscoelastic relaxation following the 2001 Kokoxili earthquake

AbstractRecent geodetic observations of shallow fault creep have illuminated increasingly complex, time-dependent slip behaviors, including quasi-steady creep and temporary accelerations, termed slow-slip events. We documented two decades of deformation on the Xidatan fault on the Tibetan Plateau measured by radar interferometry during 2003–2010 and 2015–2020 CE, to probe the temporal evolution of shallow creep and illuminate the underlying mechanisms. The geodetic observations reveal an ~80-km-long fault section with temporally decaying creep along the Xidatan fault, one of the current seismic gaps along the Kunlun fault. The transient creep is likely driven by postseismic deformation processes, dominated by viscoelastic relaxation after the 2001 Kokoxili earthquake, rather than triggered by the coseismic rupture. The transient creep behavior, indicating rate-strengthening frictional properties of the fault, contradicts the inference of locking along the Xidatan fault, based on geodetic imaging before the Kokoxili earthquake and on historical ruptures. We propose that, during the interseismic period, the frictionally unlocked shallow portions of the fault are located in the stress shadow cast by the deeper locked asperities, but they creep at resolvable rates when exposed to transient stress and stressing rate increases. We argue that stress interactions in the triple junction of the Kusai Hu, Xidatan, and Kunlun Pass faults promote complex slip behaviors throughout the earthquake cycle.

Stress intensity factor for a circumferential crack in a coke drum under two-dimensional transient temperature distribution

Coke drums are subjected to extreme temperature cycling in service, leading to circumferential cracking in the drum wall. For a deeper understanding in the cracking mechanism, stress intensity factor (SIF) for a circumferential crack in a coke drum was investigated in this paper. Based on two-dimensional heat conduction theory and classical thin shell theory, analytical solutions for the transient temperature distribution, displacement, and thermal stress in the drum wall during hot feed filling and water quench steps were determined. The weight function method (WFM) was applied to investigate the mode I SIFs based on the analytical thermal stress solutions. Numerical simulations using finite element method (FEM) were also performed to validate the analytical solutions for both the thermos-elastic field and the SIFs. The effects of shell geometry, operating parameters and material properties on the SIF during the water quench step were discussed. It is shown that the SIF increases significantly as crack depth increases. A greater shell thickness or lower diameter to thickness ratio results in lower SIFs. Lower rising rate and higher temperature of quench water can reduce the SIF. The SIF increases as the thermal conductivity and thermal expansion coefficient of the drum wall materials increase. Finally, the SIFs for Cr–Mo steel and carbon steel coke drums are also discussed.

Temporal changes of seismicity in Salton Sea Geothermal Field due to distant earthquakes and geothermal productions

SUMMARY The Salton Sea Geothermal Field (SSGF) is one of the most seismically active and geothermally productive fields in California. Here we present a detailed analysis of short-term seismicity change in SSGF from 2008 to 2013 during and right following large distant earthquakes, as well as long-term seismicity change due to geothermal productions. We first apply a GPU-based waveform matched-filter technique (WMFT) to the continuous data recorded by the Calenergy Borehole (EN) Network and detect more than 70 000 new micro-earthquakes than listed in the standard Southern California Seismic Network catalogue. We then analyse the seismicity rate changes in the SSGF associated with transient stress fluctuations triggered by regional and large teleseismic earthquakes from 1999 to 2019. We find triggered seismicity in the SSGF following seven regional M > 5.5 earthquakes. In comparison, most teleseismic earthquakes with M > 8.0 did not trigger significant seismicity rate change in the SSGF, likely indicating a frequency dependence in remote dynamic triggering. We further characterize the correlation between the long-term seismicity rate and geothermal production rates, and the temporal and spatial distribution of Guttenberg–Richter b-values inside and outside the SSGF with the newly detected catalogue. The long-term seismicity shows that events with M > 1.5 are likely correlated with net production rates, while smaller events do not show any correlation. The b-values inside the SSGF are higher than those outside the SSGF, and the locations of dynamically triggered events are close to locations with high b-values.

Botulinum toxin A injection to the external urethral sphincter for voiding dysfunction in females: A tertiary center experience.

The aim of this study is to examine the functional outcomes of ona-botulinum toxin A (BTX-A) injection into the external urethral sphincter (EUS) for female patients with nonneurogenic nonrelaxing sphincter as the underlying cause of voiding dysfunction (VD). A retrospective analysis was performed for all the patients with the urodynamic findings of higher than expected maximum urethral closure pressure (MUCP) who received their first injection during the study period. All patients were evaluated with preoperative videourodynamic study and urethral pressure profilometry and received 100 U of EUS BTX-A. Patients aged less than 18 years and those with neurogenic bladder were excluded. All patients were followed up with the free flow, postvoid residuals (PVR), and patient global impression of improvement (PGI-I) scale at 6 weeks and then at 3 monthly intervals. We identified 35 female patients with a mean age of 37.5 ± 15 years (range 18-72 years) with a mean follow-up of 20 months. More than 50% of patients had a history of prior surgical intervention and 28 (80%) patients were catheter dependent, a suprapubic catheterization, or clean intermittent self-catheterization. Mean MUCP was 97.1 ± 22 cm of water. After treatment with BTX-A, 21 (60%) patients were able to void per urethral (p = 0.02). The mean maximum flow rate (Qmax) improved from 8.8 to 11 mls/s and the mean PVRdecreased from 200 to 149 mls (p < 0.05). On multivariate analysis, we identified high preoperative PVR, high preoperative actualMUCP, and previous surgical intervention (urethral dilatation, sacral neuromodulation, and pelvic surgery) as predictors of successful voiding restoration. The mean duration of response was 4.7 months, 46% of patients requested repeat injection, and 29% were established on maintenance injections. On the 5-point PGI-I score, 13 (37%), 12 (34%), and 10 (29%) patients reported good, some, and no improvement, respectively. Quality of life was also improved in 60% of patients. Two patients had transient stress urinary incontinence (for<6 weeks) and there were no significant long-lasting adverse events. EUS BTX-A is a valid treatment option for VD considering therapeutic options are limited. The patient must be made aware of the need for repeat treatments.

Coupled thermoelastic fracture analysis of a cracked fiber reinforced composite hollow cylinder by fractional Cattaneo-Vernotte models

Coupled thermoelastic fracture problem of a fiber reinforced composite hollow cylinder containing an embedded circumferential crack is investigated in the present paper based on generalized fractional Cattaneo-Vernotte heat conduction models. The temperature and stress fields are obtained by solving the coupled partial differential equations, and then corresponding thermal axial stress with minus sign is applied to the crack surface to form a mode I crack problem. Integral transform techniques are employed to reduce the mixed boundary value problem to a series of singular integral equations. The effects of different fractional Cattaneo-Vernotte models, fractional order, convective heat transfer coefficient, volume fraction, and thermodynamic coupling coefficient on the transient temperature and thermal stress intensity factors are analyzed. The results show that each physical parameter has a significant effect on the responses, which is important to make predictions regarding the stability of crack growth, thermal fatigue life etc.

Coupled thermo-hydro-mechanical analysis of perforated cement sheath integrity during hydraulic fracturing

The wall of perforation hole was directly pressed by the high-pressure fracturing fluid, making cement integrity more challenged in fracturing process. However, the current calculation of perforated cement sheath stress neglects the influence of transient temperature variation during fracturing process. In this work, a fully coupled thermo-hydro-mechanical (THM) model incorporating the transient heat transfer process of fracturing fluid was set up to describe the transient stress variation of cement sheath during fracturing. The maximum tension stress criterion and Mohr-Coulomb criterion were chosen as the criterions for the cement failure. The proposed model was successfully verified through its excellent agreement with experimental observations. In addition, based on the proposed model, the influence of fracturing parameters and cement mechanical parameters on cement integrity was analyzed. The results illustrate that a spindle-shaped tensile-shear failure area is formed near the cement hole. The casing pressure and the cement mechanical parameters are the main controlling factors for the failure of the perforated cement sheath. The extremely low casing pressure are beneficial for maintaining cement sheath integrity. Besides that, only optimizing the Poisson's ratio or elastic modulus of cement cannot maintain the perforated cement integrity unless improving both simultaneously.

Mitofusin 2 Integrates Mitochondrial Network Remodelling, Mitophagy and Renewal of Respiratory Chain Proteins in Neurons after Oxygen and Glucose Deprivation

In attempts to develop effective therapeutic strategies to limit post-ischemic injury, mitochondria emerge as a key element determining neuronal fate. Mitochondrial damage can be alleviated by various mechanisms including mitochondrial network remodelling, mitochondrial elimination and mitochondrial protein biogenesis. However, the mechanisms regulating relationships between these phenomena are poorly understood. We hypothesized that mitofusin 2 (Mfn2), a mitochondrial GTPase involved in mitochondrial fusion, mitochondria trafficking and mitochondria and endoplasmic reticulum (ER) tethering, may act as one of linking and regulatory factors in neurons following ischemic insult. To verify this assumption, we performed temporal oxygen and glucose deprivation (OGD/R) on rat cortical primary culture to determine whether Mfn2 protein reduction affected the onset of mitophagy, subsequent mitochondrial biogenesis and thus neuronal survival. We found that Mfn2 knockdown increased neuronal susceptibility to OGD/R, prevented mitochondrial network remodelling and resulted in prolonged mitophagosomes formation in response to the insult. Next, Mfn2 knockdown was observed to be accompanied by reduced Parkin protein levels and increased Parkin accumulation on mitochondria. As for wild-type neurons, OGD/R insult was followed by an elevated mtDNA content and an increase in respiratory chain proteins. Neither of these phenomena were observed for Mfn2 knockdown neurons. Collectively, our findings showed that Mfn2 in neurons affected their response to mild and transient OGD stress, balancing the extent of defective mitochondria elimination and positively influencing mitochondrial respiratory protein levels. Our study suggests that Mfn2 is one of essential elements for neuronal response to ischemic insult, necessary for neuronal survival.

Assessing and mitigating the distortion and stress during electron beam welding of a large shell-flange structure

Electron beam (EB) welding can efficiently join large-scale components using one single autogenous pass, but it still faces challenges associated with weld-induced distortion and stress. This study investigates EB welding in a low-alloy steel thick-section shell-flange structure for a small modular reactor. A 3D thermal-metallurgical-mechanical model is developed to assess the weld-induced distortion and stress, as well as the strategy to mitigate them. When no restraint is imposed on the circumferential weld plane, an opening and sliding gap develops during the EB welding, which can cause weld defects and even process failure. Restraint through tack welds can effectively mitigate the gapping distortion, but it generates high transient tensile stress in the tack weld. Circumferentially continuous tack weld is preferential over circumferentially discrete tack welds to minimise the tensile stress. The final residual stress is insensitive to the tack-weld restraint, and the stress distribution in the steady-state welding region is broadly similar to that found in plate butt welds. However, concentration of residual stresses with high triaxiality occurs in the weld stop region, with high tensile stresses generated just behind the beam stop location, which cannot be diminished by overlap welding or change of weld stop position. The mechanisms responsible for the distortion and the transient and residual stresses are analysed. This study could provide rational basis for designing weld restraint to control distortion and guiding stress mitigation strategy for crack-susceptible region in EB weldments.

Removal of proteinase K resistant αSyn species does not correlate with cell survival in a virus vector-based Parkinson's disease mouse model

Parkinson's disease (PD) is characterized by degeneration of nigrostriatal dopaminergic neurons and accumulation of α-synuclein (αSyn) as Lewy bodies. Currently, there is no disease-modifying therapy available for PD. We have shown that a small molecular inhibitor for prolyl oligopeptidase (PREP), KYP-2047, relieves αSyn-induced toxicity in various PD models by inducing autophagy and preventing αSyn aggregation. In this study, we wanted to study the effects of PREP inhibition on different αSyn species by using cell culture and in vivo models.We used Neuro2A cells with transient αSyn overexpression and oxidative stress or proteasomal inhibition-induced αSyn aggregation to assess the effect of KYP-2047 on soluble αSyn oligomers and on cell viability. Here, the levels of soluble αSyn were measured by using ELISA, and the impact of KYP-2047 was compared to anle138b, nilotinib and deferiprone. To evaluate the effect of KYP-2047 on αSyn fibrillization in vivo, we used unilateral nigral AAV1/2-A53T-αSyn mouse model, where the KYP-2047 treatment was initiated two- or four-weeks post injection.KYP-2047 and anle138b protected cells from αSyn toxicity but interestingly, KYP-2047 did not reduce soluble αSyn oligomers. In AAV-A53T-αSyn mouse model, KYP-2047 reduced significantly proteinase K-resistant αSyn oligomers and oxidative damage related to αSyn aggregation. However, the KYP-2047 treatment that was initiated at the time of symptom onset, failed to protect the nigrostriatal dopaminergic neurons. Our results emphasize the importance of whole αSyn aggregation process in the pathology of PD and raise an important question about the forms of αSyn that are reasonable targets for PD drug therapy.

Dynamic quantitative visualization of transient shear stresses in solids

To aid in shear strength analysis, a technique combined with a time-resolved imaging scheme to achieve direct dynamic quantitative visualization of the distribution and evolution of transient shear stresses in solids through one measurement is studied. By modulating the polarization state of the elliptically polarized light transmitted or reflected from the sample, this method requires only one measurement to achieve visualization. Mathematical models of the correlation between the variation of modulated light field and the shear stresses in the plane perpendicular to the optical axis are established based on the theory of mechanics and photoelasticity. The maximum shear stresses of any section are further derived. As an example, the distribution and evolution of shear stresses induced by an ultrasonic field have been quantitatively visualized by the technique. The visualization results are in fairly good agreement with the finite element simulation results. The simplicity and efficiency of this technique are embodied in the fact that one single measurement can directly obtain the distribution of shear stresses in solids, and the measurements of dynamic shear stresses can be conveniently realized through continuous monitoring.

Investigation of the thermomechanical behavior of nonhomogeneous, layered materials with mixed-mode cracks subjected to rapid thermal shock loading

For mixed-mode, thermal shock crack problems with thermal lagging behaviors, it is difficult to obtain the transient thermal stress intensity factors (TSIFs). This paper aims to develop a method combining the Newmark method and the transient interaction energy integral method (IEIM) to extract the transient, mixed-mode TSIFs of nonhomogeneous, layered materials with mixed-mode cracks. The transient temperature field obtained by non-Fourier heat conduction theory is discretized in the spatial and temporal domains through the finite element method (FEM) and Newmark method, respectively. The effect of the continuity of thermomechanical parameters at the dual interface on the transient, mixed-mode TSIFs of nonhomogeneous, layered materials is discussed, then the fracture resistance of nonhomogeneous, layered materials is evaluated. Moreover, the maximum hoop stress criterion is utilized to obtain the crack growth angle and the equivalent, transient TSIFs of nonhomogeneous, layered materials. The influences of the interface on crack growth angle and equivalent transient TSIFs of nonhomogeneous layered materials are also studied. The present work is beneficial for the thermal design of nonhomogeneous, layered materials with mixed-mode cracks subjected to rapid thermal shock loading.

Numerical study on thermal stress fluctuation caused by coaxial-jet flow in lower head of central measurement column

In the region affected by thermal striping, the temperature fluctuation will cause alternating thermal stress in the components of nuclear reactor systems. It may lead to fatigue damage accumulation and final failure of the structure. In order to obtain the thermal stress, a simplified model of lower head of the central measurement column is built up based on the coaxial-jet flow model, and a unidirectional fluid-structure interaction simulation is conducted in the present study. The characteristics of transient thermal stress on the surface and cross-sections of the metal plate at different depths along the normal direction are numerically studied. In addition, the effects of the inlet velocity and temperature difference on the thermal stress are analyzed. The feasibility and reliability of the proposed calculation model and method are further verified by experimental data in literatures. The distribution feature of the thermal stress is similar to that of temperature. There is more than one principal frequency of thermal stress and the maximum frequency is 8 Hz. Along the depth direction, the distribution of thermal stress becomes uniform, and the thermal stress fluctuation decreases fast at first and then slows down. From the surface to the depth of 1.5 mm, peak-to-peak value decreases by 81.34% and fluctuation frequency drops to less than 5 Hz. The average thermal stress decreases in the form of slow-fast-slow with the increase of flow velocity and increases linearly with the increase of temperature difference. A high flow velocity will significantly increase the principal frequency of thermal stress fluctuation, which rises from 8 Hz to 25 Hz. A large temperature difference will significantly increase the intensity of thermal stress fluctuation.

Transient waves in a piezomagnetic half-space subjected to dynamic anti-plane loading

Propagation of transient waves in a piezomagnetic half-space, which is subjected to dynamic anti-plane-concentrated line force, is analyzed theoretically in this study. By employing Laplace transformation and Cagniard de-Hoop method, explicit closed forms of solution for the transverse displacement, shear stress, magnetic potential, and induction are obtained, and contribution from the mechanical and magnetic waves is thus expressed in the transient full-field solution. Propagation of the transient waves in the piezomagnetic half-space is then discussed in detail using numerical calculation. The results show that the magneto-mechanical coupling coefficient and location of the receiver have a significant influence on the transient response of this half-space. The magnitude of the transient shear stress is effectively reduced by the weakening magneto-mechanical coupling coefficient and the arrival time of the transient magnetic induction peak increases with decreasing magneto-mechanical coupling coefficient. In addition, it is found that the smaller the magneto-mechanical coupling coefficient, the higher the static value of the transient magnetic induction.

CysLT2R Antagonist HAMI 3379 Ameliorates Post-Stroke Depression through NLRP3 Inflammasome/Pyroptosis Pathway in Gerbils.

Post-stroke depression (PSD) is a kind of prevalent emotional disorder following stroke that usually results in slow functional recovery and even increased mortality. We had reported that the cysteinyl leukotriene receptor 2 (CysLT2R) antagonist HAMI3379 (HM3379) contributes to the improvement of neurological injury. The present study was designed to investigate the role of HM3379 in PSD-induced chronic neuroinflammation and related mechanisms in gerbils. The gerbils were subjected to transient global cerebral ischemia (tGCI) and spatial restraint stress to induce the PSD model. They were randomized to receive the vehicle or HM3379 (0.1 mg/kg, i.p.) for a consecutive 14 days. In the PSD-treated gerbils, HM3379 had noteworthy efficacy in improving the modified neurological severity score (mNSS) and depression-like behaviors, including the sucrose preference test and the forced swim test. HM3379 administration significantly mitigated neuron loss, lessened TUNEL-positive neurons, and reduced the activation of microglia in the cerebral cortex. Importantly, HM3379 downregulated protein expressions of the NOD-like receptor pyrin domain containing 3 (NLRP3) inflammasome and pyroptosis including NLRP3, cleaved caspase-1, interleukin-1β (IL-1β), IL-18, cleaved gasdermin-N domain (GSDMD-N), and apoptosis-associated speck-like protein containing a caspase activation and recruitment domain (ASC). Mechanistically, HM3379 could repress pyroptosis via inhibiting NLRP3 inflammasome activation under oxygen-glucose deprivation (OGD) stimulation. Knockdown of CysLT2R by short hairpin RNA (shRNA) or overexpression of CysLT2R by lentivirus (LV)-CysLT2R could abolish or restore the anti-depression effect of HM3379. Our results demonstrated that the selective CysLT2R antagonist HM3379 has beneficial effects on PSD, partially by suppressing the NLRP3 inflammasome/pyroptosis pathway.

Screening of salt stress in the overexpressed type of Arabidopsis thaliana (L.) Heynh. for the identification of significant hub genes using a systems biology approach

Worldwide, it is known that abiotic and biotic stresses can affect the production of crops by a declining trend. To control the situation, SnRK2 (a subfamily 2 of SNF1-related protein kinase) overexpression levels can induce salt tolerance. This study used a dataset for 2 types of Arabidopsis thaliana including the wild and PtSnRK2.7 overexpressed in mock and salt conditions to compare and identify the salt stress-responsive genes. A computational systems biology approach was employed to identify the differentially expressed genes and determine their mechanisms in terms of molecular functionalities, cellular components, KEGG enrichment pathways and plant ontology analyses. The results indicate that the 15 genes identified for PtSnRK2.7 overexpressed type in mock against salt conditions were upregulated (AT1G19180 and AT2G23150 were downregulated) and related to various environmental stresses. Furthermore, 8 out of 15 identified genes were downregulated for the wild type exposed to salt stress and the rest were upregulated. And, the only upregulated gene found differentially expressed between wild and overexpressed types in salt stress conditions was AT4G15110. In contrast, the other two AT1G15010 and AT4G19430 were downregulated and involved in transient stress and inactivation of chloroplast, respectively. Taken together, it has been shown that A. thaliana PtSnRK2.7 overexpressed type can resist salt stress. Finally, more experimental studies and computational systems biology methodologies are needed to reveal and confirm the responsive gene for salt stress in A. thaliana.

TREATMENT OUTCOMES OF BLADDER NECK CONTRACTURE AFTER TRANSURETHRAL PROSTATE SURGERY

(Introduction) A known complication of the surgical treatment of benign prostatic hyperplasia (BPH) is bladder neck contracture (BNC). BNC is often treated using transurethral incision of the bladder neck (TUI-BN); however, there are few reports on the outcomes of TUI-BN. Therefore, we examined the outcomes of patients who underwent TUI-BN after transurethral prostate surgery. (Material and methods) We retrospectively examined 25 patients who underwent TUI-BN between February 2015 and January 2021 for the following: (1) patients' characteristics; (2) the time from transurethral prostate surgery to TUI-BN; (3) the trigger of BNC diagnosis; (4) surgical procedure of BNC repair/perioperative course; (5) micturition function immediately after TUI-BN; and (6) Postoperative outcomes. (Results) The median age of the patients was 77 years, and the surgical procedures for BPH were transurethral resection of the prostate (TURP) in four cases, transurethral resection in saline plasma vaporization of the prostate (TURisP) in nine cases, and transurethral enucleation with bipolar (TUEB) in 12 cases. The median time to onset of BNC symptoms was 364 days, and 18 patients (72%) were diagnosed within 2 years. The trigger of BNC diagnosis was urinary symptoms in 21 cases, of which 16 patients had exacerbation of urination. The median duration of the surgical procedure of BNC repair was 14 min, and the incisions most frequently used (in 44% of cases) were at the 4 o'clock and 8 o'clock positions. Transient stress urinary incontinence was observed as a complication in three cases. In the 4 o'clock and 8 o'clock incisions, the maximum urine flow rate improved significantly (11.1 mL/s perioperatively vs. 20.9 mL/s postoperatively; P=0.004). These symptoms improved in 16 of the 21 symptomatic cases, and the maximum urine flow rate improved significantly (P< 0.01). The median observation period after surgery was 170 days; eight postoperative patients were lost to follow up. There were two cases of recurrence. (Conclusions) BNC is likely to develop within 2 years after transurethral prostate surgery. In this study, the success rate of the initial TUI-BN was 92%, as reoperation was required in two cases; however, the overall prognosis was good.

Climate-driven stress changes and normal fault behavior in the Lake Malawi (Nyasa) Rift, East Africa

Climate-triggered fluctuations of surface masses, including ice and water, can cause transient stress in the Earth's crust, further affecting the slip behavior of faults over different temporal and length scales. In particular, lakes developed within active continental rifts may modulate the stress states and slip rates of rift border faults and intrarift faults. Here, we utilize a numerical model in a case study of the Malawi (Nyasa) Rift to understand the response of faults to mass fluctuations on the Earth's surface. The water level of Lake Malawi rose 600 m over the last 150 kyr, and significantly influenced the stress state of faults in rift valley. We find that such water load fluctuations can exert 4.6 MPa normal stress on fault planes and produce a negative Coulomb stress (down to −2.0 MPa) on fault planes as well as a pronounced reduction of slip (∼2 m) on fault planes within the rift. Moreover, along-strike differences in fault geometries and their position relative to the center of the water column load resulted in variable along-strike stress and slip changes. These results suggest that lakes that develop within continental rifts play an important role in the evolution of extensional faulting. Our case study provides a basis for evaluating the relationship between climate-driven surface mass variations and the subsurface stress state of fault planes and associated seismic potentials.

Viscoelastoplastic classification of cementitious suspensions: transient and non-linear flow analysis in rotational and oscillatory shear flows

Rheological modeling of special concretes such as ultra-high performance concretes (UHPCs), self-compacting concretes (SCCs), or environmentally friendly concretes with low clinker contents but containing many fine particles increases model complexity because high amounts of colloidal and fine particles and complex chemistry result in strongly non-Newtonian rheological behavior. Straight-forward viscoplastic rheological models such as the well-known Bingham- or Herschel-Bulkley approach do not fit the flow behavior on a large scale at and lead to boundary value problems in numerical flow simulations. Increased viscoelastic properties due to chemical admixtures are not described by pure viscoplasticity analysis methods. To fill this gap, our research presents viscoplastic and viscoelastic linear and non-linear rheological characterization methods for common and strongly non-Newtonian cement pastes and combines the methods for a comprehensive viscoelastoplastic modeling of cementitious building materials. We illustrate and discuss the benefits and boundaries of each measurement technique in dependence of cementitious paste complexity. Three solid volume fractions from phi = 0.45 to 0.55 and three different flowability ranges, adjusted through varying superplasticizer amounts, were investigated in respect of steady-state and transient yield stress, viscosity, and non-linear viscoelastic material properties. Our results reveal that with increasing solid volume fraction and polymer amount, viscoelastoplastic modeling describes rheological flow on a large flow scale more appropriately than common viscoplastic methods. The results show a new approach for a full quantitative and qualitative rheological classification of cementitious building materials and thus improve the understanding of densely packed colloidal cementitious suspensions. The findings serve as prospective guideline to model complex cementitious building materials both at low and high shear rates, and to find an appropriate rheological description at the boundaries of flow.Graphical abstract

High Stress Deformation and Short‐Term Thermal Pulse Preserved in Pyroxene Microstructures From Exhumed Lower Crustal Seismogenic Faults (Lofoten, Norway)

AbstractEarthquake rupture in strong, anhydrous lower continental crust requires high brittle failure stresses unless high pore fluid pressures are present. Several mechanisms proposed to generate high stresses at depth imply transient loading driven by a spectrum of stress changes, ranging from highly localized stress amplifications to crustal‐scale stress transfers. High transient stresses up to GPa magnitude are proposed by field and modeling studies, but the evidence for transient prerupture loading is often difficult to extract from the geological record due to overprinting by coseismic damage and slip. However, the local preservation of deformation microstructures indicative of crystal‐plastic and brittle deformation associated with the seismic cycle in the lower crust offers the opportunity to constrain the progression of deformation before, during and after rupture, including stress and temperature evolution. Here, detailed study of pyroxene microstructures characterizes the short‐term evolution of high‐stress deformation and temperature changes experienced before and during lower crustal earthquake rupture. Pyroxenes are sampled from pseudotachylyte‐bearing faults and damage zones of lower crustal earthquakes recorded in the exhumed granulite facies terrane of Lofoten, northern Norway. The progressive sequence of microstructures indicates localized high‐stress (at the GPa level) prerupture loading accommodated by low‐temperature plasticity, followed by coseismic pulverization‐style fragmentation and subsequent grain growth triggered by the short‐term heat pulse associated with frictional sliding. Thus, up to GPa‐level transient high stress (both differential and shear) leading to earthquake nucleation in the dry lower crust can occur in nature, and be preserved in the fault rock microstructure.

Systematic Analysis and Characterization of Extreme Failure for IGCT in MMC-HVdc System—Part I: Device Structure, Explosion Characteristics, and Optimization

Explosion proof of power devices is important for the safe operation of high voltage direct current power transmission system based on modular multilevel converter (MMC-HVdc). Comparison of the main commercial power devices’ structures shows that the integrated gate commutated thyristor (IGCT) has the simplest housing structure, which is suitable for withstanding the extreme fault in the MMC-HVdc system. Explosion proof tests of IGCT are carried out with different distribution of destruction positions under the extreme failure in the MMC-HVdc system. The maximum surge current of IGCT is between 600 and 700 kA when 18 mF capacitor with 4500 V is discharged. IGCT with evenly distributed destruction positions shows excellent explosion proof, while IGCT with edge focusing destruction positions shows poor explosion proof. Further thermal analysis with simulation shows that IGCT's ceramic shell may suffer a huge transient thermal stress when the destruction positions focus on the edge areas. A designed gas pressure tolerance test shows that the gas pressure is in the safe area which IGCT can withstand under the extreme failure. This means that the thermal stress can be regarded as the main cause of IGCT's explosion phenomenon. Based on the explosion mechanism, an optimized IGCT with controlled punch-through design in the central area is proposed to avoid the edge area destruction under the extreme failure. And explosion proof experiment of optimized IGCT validates its excellent explosion proof under the extreme failure in the MMC-HVdc system.