Inherent Stress Research Articles

A grey incidence-based algorithm for optimization of accelerated degradation test

PurposeThe purpose of this paper is to optimize the degradation test for products subject to multiple types of inherent stresses and external random shocks. The mechanism that shows how the variables to be optimized influence the considered multiple objectives is also aimed to be explored by using the grey incidence analysis (GIA) model.Design/methodology/approachThe Gamma process is employed to model the influences of different types of stresses and external random shocks. The GIA model is introduced to transfer multiple considered objectives as a comprehensive degree of grey incidence. The particle swarm optimization is integrated to search the globally optimal value of the characteristic variables to be optimized.FindingsThe acceleration of tested stresses and external random shocks both make the engineering systems become more vulnerable to the inherent degradation. And, the Kriging model can provide guidance of searching the optimal values of test characteristic variables and mitigate the computation burden. The grey incidence model can make the optimization focused and improve the optimality of objective values.Originality/valueThe proposed method can effectively overcome the drawbacks brought by the limitation of test data and can specify the dependence strength between the inherent degradation and external random shock. The computation cost and accuracy of optimization can be simultaneously ensured by the proposed model.

An analytic approach for nonlinear collisional fragmentation model arising in bubble column

The phenomenon of coagulation and breakage of particles plays a pivotal role in diverse fields. It aids in tracking the development of aerosols and granules in the pharmaceutical sector, coagulation or breakage of droplets in chemical engineering, understanding blood clotting mechanisms in biology, and facilitating cheese production through the action of enzymes within the dairy industry. A significant portion of research in this direction concentrates on coagulation or linear breakage processes. In the case of linear case, bubble particles break down due to inherent stresses or specific conditions of the breakage event. However, in many practical situations, particle division is primarily due to forces exerted during collisions between particles, necessitating an approach that accounts for nonlinear collisional breakage. Despite its critical role in a wide array of engineering and physical operations, the study of this nonlinear fragmentation phenomenon has not been extensively pursued. This article introduces an innovative semi-analytical method that leverages the beyond linear use of equation superposition function to address the nonlinear integro-partial differential model of collisional breakage population balance. This approach is versatile, allowing for the resolution of both linear/nonlinear equations while sidestepping the complexities associated with discretization of domain. To assess the precision of this method, we conduct a thorough convergence analysis. This process utilizes the principle of contractive mapping in the Banach space, a globally recognized strategy for verifying convergence. We explore a variety of kernel parameters associated with collisional kernels, alongside breakage and initial distribution functions, to derive novel iterative solutions. Comparing our findings with those obtained through the finite volume method regarding number density functions and their integral moments, we demonstrate the reliability and accuracy of our approach. The consistency and correctness of our method are further validated by depicting the errors between the exact and approximated solutions in graphical and tabular formats.

A microstructural thermo‐elastoplastic analysis of the mushy zone during laser beam welding

AbstractAs a modern method of contact free fusion, laser beam welding has gained importance in recent years. This is due to both the possibiliy of a high advance speed of the laser and low thermal distortion of the components compared to other welding processes, see Dal and Fabbro. These beneficial process properties follow from a focused laser, which thus results in a precise energy input. In addition, laser beam welding processes can be automated which makes the process attractive for a wide range of applications, cf. Dilthey. Nevertheless, various influences, like the temperature gradient, the chemical composition or process parameters, may have an effect on the occurrence of so‐called solidification cracks. Solidification cracks arise during solidification and occur in the area of the mushy zone, which is located behind the melt pool. The material behavior in the mushy zone is governed by a dendritic morphology. Due to this, liquid phase inclusions may occur in some parts of the mushy zone, see Hills et al.. When these trapped areas solidify, no further liquid phase can follow and a negative pressure is created. The resulting stresses can then lead to solidification cracks. In further studies, the geometry of the dendritic morphology will be generated on the basis of previous phase field simulations. These describe the dendrite growth controlled by the chemical concentration. The resulting geometry will then be simulated using the possibilities of a thermo‐elastoplastic material model, which will enable temperature‐driven imitation of growth. This contribution addresses the evolving state of the dendritic microstructure in a simplified manner. Therefore, for the first study, a simplified morphology is used, that is, no secondary arms and an elliptical geometry of the dendrites is assumed. Thermal as well as elastoplastic effects are already taken into account, in order to represent the inherent stress and strain states in the microstructure. These may be related to critical states leading to failure in the future.

Inhibition of nucleo-cytoplasmic proteasome translocation by the aromatic amino acids or silencing Sestrin3-their sensing mediator-is tumor suppressive.

The proteasome, the catalytic arm of the ubiquitin system, is regulated via its dynamic compartmentation between the nucleus and the cytoplasm, among other mechanisms. Under amino acid shortage, the proteolytic complex is translocated to the cytoplasm, where it stimulates proteolysis to supplement recycled amino acids for essential protein synthesis. This response ismediated via the mTOR pathway and the lack of the three aromatic amino acids Tyr, Trp, and Phe (YWF). mTOR activation by supplementation of the triad inhibits proteasome translocation, leading to cell death. We now show that tumoral inherent stress conditions result in translocation of the proteasome from the nucleus to the cytosol. We further showthat the modulation of the signaling cascade governed by YWF is applicable also to non-starved cells by using higher concentration of the triad to achieve a surplus relative to all other amino acids. Based on these two phenomena, we found that the modulation of stress signals via the administration of YWF leads to nuclear proteasome sequestration and inhibition of growth of xenograft, spontaneous, and metastatic mouse tumor models. In correlation with the observed effect of YWF on tumors, we found - using transcriptomic and proteomic analyses - that the triad affects various cellular processes related to cell proliferation, migration, and death. In addition, Sestrin3-a mediator of YWF sensing upstream of mTOR-is essential for proteasome translocation, and therefore plays a pro-tumorigenic role, positioning it as a potential oncogene. This newly identified approach for hijacking the cellular "satiety center" carries therefore potential therapeutic implications for cancer.

Unravelling NbSe2 single crystal: First principle insights, optical properties, synthesis and X-ray diffraction profile investigation

Niobium diselenide (NbSe2) crystals were synthesized using the chemical vapour transport (CVT) technique. The Generalized Gradient Approximation (GGA) method was used in the density functional theory (DFT) calculation. The Perdew-Burke-Ernzerhof (PBE) pseudopotential function was utilised to emphasise the structural, electrical, elastic constant, and optical characteristics of the hexagonal P63/mmc symmetric structured crystalline phase of NbSe2. Additionally, the density of states (DOS) revealed that, at the Fermi level, the Nb (3d) states predominated, with the Se (5p) and Se (5 s) states playing a minor role. The band structure confirmed the crystal's metallic nature, which showed an overlap between the conduction and valence bands. Scherrer method, Williamson-Hall (WH) analysis, Size-Strain Plot (SSP), and Halder-Wagner (HW) plot utilising uniform deformation model (UDM), uniform stress deformation model (USDM), and uniform deformation energy density model (UDEDM) models were used to investigate the X-ray diffraction (XRD) profile. The crystallite size, inherent stress, strain, and energy density parameters were estimated. Optical microscopy and transmission electron microscopy (TEM) had both been used to study surface morphology.

Development of accurate contour residual stress measurement technique for sustainable structural integrity assessment in additive manufacturing

Abstract Accurate analysis of residual stress present within an engineering component plays a fundamental role to its sustainable structural integrity assessment. This is particularly important for a safety critical component within the power generation sectors, aerospace, and oil and gas industries. The accurate stress analysis not only allows operators to determine the life remaining in a component but also avoid over-conservative estimates and thereby contribute to life extension of engineering plants and components. By utilizing and unifying multiple residual stress analysis tools of different nature a robust and more accurate method of stress analysis is achieved. The main aim of the current study focusses on the development and optimization of a robust residual stress tool based on the contour technique to accurately analyse inherent stress in an engineering component.

The Moral Impacts of Organizational Stress on Correctional Officers

Organizational stress (i.e., structural aspects of the organization such as excessive workload, shiftwork, gossip) has long been found by public safety personnel to be more impactful on their health and wellness than operational stress (i.e., inherent stresses of the job such as altercations, intervention in suicide behaviors). In the current study, which engages semi-structured interviews conducted with 28 correctional officers employed at one provincial prison in Atlantic Canada, we unpack through a lens of moral distress four prevalent sources of organizational stress among correctional officers that emerged in the data without categories precogitated, with a focus on participant experiences and expressed similarities across accounts: (1) management, (2) staff retention, (3) training needs, (4) lack of mental health support. Findings indicate organizational stress has a significant impact on correctional officers and these sources of organizational stress are exacerbated by officers’ moral and ethical vulnerabilities emergent from their conditions of employment. We recommend several practical changes to ease the strains and moral harms felt by correctional officers and better support their mental health and well-being, such as increasing staffing levels, providing more education and training opportunities for frontline officers and senior leaders, and providing more adequate mental health support for correctional officers.

Choosing between commercially pure titanium and Ti-6Al-4V gyroid structures for orthopedic applications: An analysis through Timoshenko beam theory, the Gibson-Ashby model and experimental methods

For decades, research has focused on using gyroid lattice structures to prevent stress-induced osteopenia and improve osseointegration by promoting cell adhesion and transition, particularly in cases where implant removal is not desired after complete healing. Despite these advantages, in-depth research is still needed for innovative biomedical implants to reach optimum functionality. Although commercially pure titanium (Cp-Ti) and Ti6Al4V are both popular materials for standalone bone implants, they are not likely paired within the same application due to mechanical property differences. This study proposes a case-specific workflow to support orthopedic implant design considerations, by analytically and experimentally investigating the mechanical response of additively manufactured lattice gyroid structures in both Cp-Ti and Ti6Al4V with different porosity rates. The experimental results of both materials indicate a significant decrease in the elastic modulus against two employed analytical methods, Gibson-Ashby model and Timoshenko beam theory. This is linked to inherent manufacturing-induced stress concentrations on the physical gyroids. The experimental outcome presents itself significantly closer to the predictions of Timoshenko beam theory compared to Gibson Ashby method. Both gyroid titanium structures are loyal to Timoshenko theory, displaying a combination of multi deformation behaviors instead of one-way deformation. The deformation response of Ti6Al4V showed a 45⁰ shear band while Cp-Ti exhibited smoother deformation during compression. Higher porosity rates led to an increase in ductility due to extended horizontal plateau regions in both Cp-Ti and Ti6Al4V lattice structures. The results provide valuable comparative insight and considerations on the material choice for gyroid lattice structures within bone implants.

A structural curve with reduced stress concentration and its elastic–plastic failure analysis

Stress concentration represents a significant concern in engineering failure analysis, influencing various failure mechanisms. Mitigating stress concentration requires the implementation of an efficient transition curve. However, traditional transition curve designs, including single-curvature, multi-curvature, elliptical, and streamlined types, prove to be suboptimal solutions. This study proposes an innovative transition curve scheme inspired by biological structures to mitigate inherent stress concentration at transition regions. Tensile tests are performed on specimens featuring various transition curve schemes to assess their mechanical performance and validate the superiority of the proposed scheme. Finite element simulation is employed to analyze stress distribution under tension and bending for the various schemes. Digital Image Correlation experiments were performed to validate the numerical simulations. Results demonstrate that the proposed scheme enhances load-bearing capacity, narrows the range of high-stress and yield regions, and optimizes force flow. By incorporating critical position and limit values of the transition curve, the proposed scheme effectively disperses stress, reducing the stress concentration factor to below 1.03. This design methodology can be applied to develop transition curves for shaft shoulders and variable section parts, thereby enhancing safety, structural stability, and durability. Ultimately, this scheme extends the lifespan of the structure.

Improving vitrification efficiency of human in vitro matured oocytes by the addition of LEA proteins.

Can the addition of late embryogenesis-abundant (LEA) proteins as a cryoprotective agent during the vitrification cryopreservation of in vitro matured oocytes enhance their developmental potential after fertilization? LEA proteins improve the developmental potential of human in vitro matured oocytes following cryopreservation, mostly by downregulating FOS genes, reducing oxidative stress, and inhibiting the formation of ice crystals. Various factors in the vitrification process, including cryoprotectant toxicity, osmotic stress, and ice crystal formation during rewarming, can cause fatal damage to oocytes, thereby affecting the oocytes developmental potential and subsequent clinical outcomes. Recent studies have shown that LEA proteins possess high hydrophilicity and inherent stress tolerance, and can reduce low-temperature damage, although the molecular mechanism it exerts protective effects is still unclear. Two LEA proteins extracted and purified by us were added to solutions for vitrification-warming of oocytes at concentrations of 10, 100, and 200 µg/mL, to determine the optimal protective concentration for each protein. Individual oocyte samples were collected for transcriptomic analysis, with each group consisting of three sample replicates. Immature oocytes were collected from patients who were undergoing combined in vitro fertilization (IVF) treatment and who had met the designated inclusion and exclusion criteria. These oocytes underwent in vitro maturation (IVM) culture for experimental research. A fluorescence microscope was used to detect the levels of mitochondrial membrane potential (MMP), reactive oxygen species (ROS), and calcium in the mitochondria of vitrified-warmed human oocytes treated with different concentrations of LEA proteins, and the protective effect of the protein on mitochondrial function was assessed. The levels of intracellular ice recrystallization inhibition (IRI) in human oocytes after vitrification-warming were characterized by the cryomicroscope, to determine the LEA proteins inhibitory effect on recrystallization. By analyzing transcriptome sequencing data to investigate the potential mechanism through which LEA proteins exert their cryoprotective effects. The secondary structures of AfrLEA2 and AfrLEA3m proteins were shown to consist of a large number of α-helices and the proteins were shown to be highly hydrophilic, in agreement with previous reports. Confocal microscopy results showed that the immunofluorescence of AfrLEA2-FITC and AfrLEA3m-FITC-labeled proteins appeared to be extracellular and did not penetrate the cell membrane compared with the fluorescein isothiocyanate (FITC) control group, indicating that both AfrLEA2 and AfrLEA3m proteins were extracellular. The group treated with 100 µg/mL AfrLEA2 or AfrLEA3mprotein had more uniform cytoplasmic particles and fewer vacuoles compared to the 10 and 200 µg/mL groups and were closest to the fresh group. In the 100 µg/mL groups, MMPs were significantly higher while ROS and calcium levels were significantly lower than those in the control group and were closer to the levels observed in fresh oocytes. Meanwhile, 100 µg/mL of AfrLEA2 or AfrLEA3m protein caused smaller ice crystal formation in the IRI assay compared to the control group treated with dimethylsulphoxide (DMSO) and ethylene glycol (EG); thus, the recrystallization inhibition was superior to that with the conventional cryoprotectants DMSO and EG. Further results revealed that the proteins improved the developmental potential of human oocytes following cryopreservation, likely by downregulating FOS genes and reducing oxidative stress. The in vitro-matured metaphase II (IVM-MII) oocytes used in the study, due to ethical constraints, may not accurately reflect the condition of MII oocytes in general. The AfrLEA2 and AfrLEA3m proteins are recombinant proteins and their synthetic stability needs to be further explored. LEA proteins, as a non-toxic and effective cryoprotectant, can reduce the cryoinjury of oocytes during cryopreservation. It provides a new promising method for cryopreservation of various cell types. This work was supported by the National Key Research and Development Program of China (2022YFC2703000) and the National Natural Science Foundation of China (52206064). The authors declare no competing interest. N/A.

The DNA Damage Response (DDR) landscape of endometrial cancer defines discrete disease subtypes and reveals therapeutic opportunities.

Genome maintenance is an enabling characteristic that allows neoplastic cells to tolerate the inherent stresses of tumorigenesis and evade therapy-induced genotoxicity. Neoplastic cells also deploy many mis-expressed germ cell proteins termed Cancer Testes Antigens (CTAs) to promote genome maintenance and survival. Here, we present the first comprehensive characterization of the DNA Damage Response (DDR) and CTA transcriptional landscapes of endometrial cancer in relation to conventional histological and molecular subtypes. We show endometrial serous carcinoma (ESC), an aggressive endometrial cancer subtype, is defined by gene expression signatures comprising members of the Replication Fork Protection Complex (RFPC) and Fanconi Anemia (FA) pathway and CTAs with mitotic functions. DDR and CTA-based profiling also defines a subset of highly aggressive endometrioid endometrial carcinomas (EEC) with poor clinical outcomes that share similar profiles to ESC yet have distinct characteristics based on conventional histological and genomic features. Using an unbiased CRISPR-based genetic screen and a candidate gene approach, we confirm that DDR and CTA genes that constitute the ESC and related EEC gene signatures are required for proliferation and therapy-resistance of cultured endometrial cancer cells. Our study validates the use of DDR and CTA-based tumor classifiers and reveals new vulnerabilities of aggressive endometrial cancer where none currently exist.

Computational Evaluation of Weaving Process on Mechanical Stiffness of Plain Weave Fabric

Inherent structural stress in a plain weave is induced during the formation process of fabrics, and its evaluation is useful for estimating the mechanical stiffness of weaves. In this study, the effect of inherent stress distributed in a weave fabric was investigated to estimate its mechanical stiffness. Here, a numerical simulation method that imitates the fabrication process of fabrics is proposed to evaluate stiffness. A diagram illustrating the weaving process is defined in this evaluation method. For computational analysis, a unit cell model used in homogenization was developed based on the structural periodicity of the plain weave structure using the finite element method. The weaving state was accomplished by simulating the weaving behavior in this model. The weaving state included the geometric shape and stress/strain data. Subsequently, a model was built to estimate the mechanical stiffness based on the weaving state data. Finally, a uniaxial tensile simulation was conducted using the numerical model. Using this evaluation method, the effect of inherent stress on the mechanical stiffness of weaves was quantified, which indicated that the tensile stiffness improved in a small strain range. The effect gradually decreased as the tension progressed.

Investigating the Feasibility of Using a Wearable Device to Measure Physiologic Health Data in Emergency Nurses and Residents: Observational Cohort Study.

Emergency departments play a pivotal role in the US health care system, with high use rates and inherent stress placed on patients, patient care, and clinicians. The impact of the emergency department environment on the health and well-being of emergency residents and nurses can be seen in worsening rates of burnout and cardiovascular health. Research on clinician health has historically been completed outside of clinical areas and not personalized to the individual. The expansion of digital technology, specifically wearable devices, may enhance the ability to understand how health care environments impact clinicians. The primary objective of this pilot study was to assess the feasibility and acceptability of using wearable devices to measure and record physiologic data from emergency nurses and resident physicians. Understanding strategies that are accepted and used by clinicians is critical prior to launching larger investigations aimed at improving outcomes. This was a longitudinal pilot study conducted at an academic, urban, level 1 trauma center. A total of 20 participants, including emergency medicine resident physicians and nurses, were equipped with a wearable device (WHOOP band) and access to a mobile health platform for 6 weeks. Baseline surveys assessed burnout, mental health, and expectations of the device and experience. Participants provided open-ended feedback on the device and platform, contributing to the assessment of acceptance, adoption, and use of the wearable device. Secondary measures explored early signs and variations in heart rate variability, sleep, recovery, burnout, and mental health assessments. Of the 20 participants, 10 consistently used the wearable device. Feedback highlighted varying experiences with the device, with a preference for more common wearables like the Apple Watch or Fitbit. Resident physicians demonstrated higher engagement with the device and platform as compared with nurses. Baseline mental health assessments indicated mild anxiety and depressive symptoms among participants. The Professional Fulfillment Index revealed low professional fulfillment, moderate workplace exhaustion, and interpersonal disengagement. This pilot study underscores the potential of wearable devices in monitoring emergency clinicians' physiologic data but reveals challenges related to device preferences and engagement. The key takeaway is the necessity to optimize device and platform design for clinician use. Larger, randomized trials are recommended to further explore and refine strategies for leveraging wearable technology to support the well-being of the emergency workforce.

Adapting to stress: The effects of hibernation and hibernacula temperature on the hepatic transcriptome of Rhinolophus pusillus.

Hibernation, a survival strategy in mammals for extreme climates, induces physiological phenomena such as ischemia-reperfusion and metabolic shifts that hold great potential for advancements in modern medicine. Despite this, the molecular mechanisms underpinning hibernation remain largely unclear. This study used RNA-seq and Iso-seq techniques to investigate the changes in liver transcriptome expression of Rhinolophus pusillus during hibernation and active periods, as well as under different microhabitat temperatures. We identified 11 457 differentially expressed genes during hibernation and active periods, of which 395 showed significant differential expression. Genes associated with fatty acid catabolism were significantly upregulated during hibernation, whereas genes related to carbohydrate metabolism and glycogen synthesis were downregulated. Conversely, immune-related genes displayed differential expression patterns: genes tied to innate immunity were significantly upregulated, while those linked to adaptive immunity and inflammatory response were downregulated. The analysis of transcriptomic data obtained from different microhabitat temperatures revealed that R. pusillus exhibited an upregulation of genes associated with lipid metabolism in lower microhabitat temperature. This upregulation facilitated an enhanced utilization rate of triglyceride, ultimately resulting in increased energy provision for the organism. Additionally, R. pusillus upregulated gluconeogenesis-related genes regardless of the microhabitat temperature, demonstrating the importance of maintaining blood glucose levels during hibernation. Our transcriptomic data reveal that these changes in liver gene expression optimize energy allocation during hibernation, suggesting that liver tissue adaptively responds to the inherent stress of its function during hibernation. This study sheds light on the role of differential gene expression in promoting more efficient energy allocation during hibernation. It contributes to our understanding of how liver tissue adapts to the stressors associated with this state.

Addressing the inherent stress non-uniformity in dynamic hollow cylinder testing

The Dynamic Hollow Cylinder Apparatus (DHCA) is renowned for its ability to subject soil samples to various cyclic stress paths, allowing for the investigation of the dynamic behavior of soils under complex cyclic loading conditions. This note explores the errors arising from the stress non-uniformity along the height of DHCA samples and examines their impact on the measured soil dynamic properties. After discussing the two globally used DHCA types, this study presents the stiffness and damping of sand derived from a set of Dynamic Hollow Cylinder experiments covering a wide range of dynamic stress paths and shear strain amplitudes. It is highlighted that the deviation of the results from established degradation models is primarily attributed to the errors associated with the stress non-uniformity, leading to up to a tenfold underestimation within the medium strain range. A simple correction to the shear stress amplitude calculation is proposed to minimize the impact of stress non-uniformity and improve the accuracy of the test results.

Designing hydrogen-free diamond like multilayer carbon coatings for superior mechanical and tribological performance

Diamond like carbon (DLC) coatings are extensively employed for their outstanding mechanical and tribological properties. To overcome the inherent high residual stress, therefore brittleness, DLC coatings with multilayer architecture were developed in the form of stacking alternate hard and soft layers to avoid premature failure under severe loading conditions. The current study was designed to investigate the impact of bilayer thickness (hard & soft) on wear of multilayer DLC particularly at high contact stress (2.0 GPa, 2.7 GPa, 3.0 GPa, 3.4 GPa). Seven DLC multilayer (1:1 bilayer ratio) samples with 1, 2, 5, 10, 20, 40, 80 bilayers were deposited on 440C steel and the overall coating thickness was mainatined at ∼1 µm. Moreover, the bilayer thickness effect was determined on mechanical, scratch adhesion and structural properties. Transmission electron microscope (TEM) was used to visualize discrete hard and soft layers in 80 bilayers (∼6 nm thin layer). G peak suppression and ID/IG increment were observed with reduction in bilayer thickness. Hardness, modulus, elastic strain to failure (H/E), plastic deformation resistance (H3/E2) and residual stresses showed an inverse relation with bilayer thickness. Furthermore, micro scratch adhesion decreases with layer thickness reduction. Only 100 nm and above bilayer thickness samples (1, 2, 5, 10 bilayers) could survive under high contact stress while the other three (20, 40, 80 bilayers) showed brittle failure using pin-on-disc tribometer. Additionally, 10 bilayers (100 nm thickness) produced the minimum wear (∼7.9 ×10−8 mm3/Nm) at 80 N.

A comparative analysis of depressive-like behavior: Exploring sex-related differences and insights.

Profiling the variability related to the estrous cycle is essential for assessing depressive-like behavior and screening drugs. This study compares circulating plasma corticosterone levels [CORT] and behavioral alterations in mice exposed to sucrose preference, forced swimming, and tail suspension tests (SPT, FST, and TST, respectively). While SPT exposure did not significantly alter [CORT], FST and TST showed notable changes. Mice in the TST exhibited increased movement and decreased immobility time compared to FST, suggesting a lower likelihood of depressive-like behavior in male mice. Notably, during the proestrus phase, female mice displayed the highest tendency for depressive-like behavior and elevated [CORT], but similar response to antidepressants (imipramine and fluoxetine). The inherent stress of the FST and TST tasks appears to influence [CORT] as well as depressant and antidepressant effects. These comparisons provide valuable insights for further behavioral phenotyping, model sensitivity assessment, and deepen our neurobiological understanding of depression in the context of drug screening.

Rolling Shear Strength of Cross Laminated Timber (CLT)—Testing, Evaluation, and Design

Cross laminated timber (CLT), with its typical orthogonal layering and exposure to out-of-plane bending, develops inherent rolling shear stresses. These stresses need to be checked during the ultimate limit state design process. With the ongoing revision of Eurocode 5, a discussion regarding the characteristic value of the rolling shear strength of CLT has arisen. One obstacle in the discussion is seen in the lack of harmonized regulations concerning how to determine rolling shear properties. This circumstance manifests in the greatly diverging test results of different institutions testing the rolling shear strength. The paper at hand aims to propose a candidate for such harmonized regulations. To achieve this, the most common test setups, such as the inclined shear test, three- and four-point bending tests, etc., were numerically and experimentally investigated. Within the numerical investigations, a comparison of the most common calculation methods (Timoshenko beam theory, modified γ-method, Shear Analogy Method, and Finite Element Analysis) for evaluating rolling shear stresses was included. In the experimental program, parameters such as the specimen width, number, and thickness of the cross layer(s), shear length, optional reinforcement against the stresses perpendicular to the grain, and the overall test setup were varied. It was found that the used test setups themselves and the area of the cross layer(s) (shear length, number, and thickness of the cross layer(s)) have a major impact on the rolling shear strength. In contrast, no effect was found from the calculation methods. Based on these findings and on a database of approx. 300 four-point bending rolling shear tests on CLT specimens from five well-established CLT manufacturers, a model for the regulation of the rolling shear strength of CLT is proposed, in combination with a corresponding four-point bending test setup. Afterwards, with two additionally conducted four-point bending test series, the proposed model is successfully validated. The conclusions and recommendations in respect to the test setup (four-point bending), evaluation procedure (Timoshenko beam theory), reference characteristic rolling shear strength, and the model, which allows adapting the reference rolling shear strength to individual conditions, are seen as a worthy basis for a more objective discussion on this topic.

Inherent stress concentration in patterned glass

Inherent stress concentration in patterned glass

A thicker Antarctic ice stream during the mid-Pliocene warm period

Ice streams regulate most ice mass loss in Antarctica. Determining ice stream response to warmer conditions during the Pliocene could provide insights into their future behaviour, but this is hindered by a poor representation of subglacial topography in ice-sheet models. We address this limitation using a high-resolution model for Dronning Maud Land (East Antarctica). We show that contrary to dynamic thinning of the region’s ice streams following ice-shelf collapse, the largest ice stream, Jutulstraumen, thickens by 700 m despite lying on a retrograde bed slope. We attribute this counterintuitive thickening to a shallower Pliocene subglacial topography and inherent high lateral stresses at its flux gate. These conditions constrict ice drainage and, combined with increased snowfall, allow ice accumulation upstream. Similar stress balances and increased precipitation projections occur across 27% of present-day East Antarctica, and understanding how lateral stresses regulate ice-stream discharge is necessary for accurately assessing Antarctica’s future sea-level rise contribution.