Collapse Stress Research Articles

Dynamic Mechanical Properties and Constitutive Modeling of Polyurethane Microporous Elastomers.

The present study fabricated samples of polyurethane elastomers (PUEs) with three distinct densities and assessed their mechanical responses using split Hopkinson pressure bar (SHPB) tests. The findings reveal a significant increase in PUE stress with increasing strain rate and density. To further investigate the influence of strain rate sensitivity on PUEs, a strain rate sensitivity coefficient was employed to quantify the impact of strain rate on the mechanical properties of PUEs. Separate quantifications were performed for collapse stress, plateau stress, and densification strain as indicators of the strain rate sensitivity coefficient. The results demonstrate that the collapse stress sensitivity coefficient was notably affected by the applied strain rate. Additionally, both collapse and plateau stresses exhibited an increase with increasing density, which could be described by a power function relationship. Based on the theory of strain energy function, a constitutive model considering density and strain rate effects was developed to describe the stress-strain behavior of PUEs under various densities and strain rates. A comparison between this constitutive relationship and experimental results showed good agreement, highlighting its potential in describing dynamic mechanical behavior.

Continuum models for meso-scale simulations of HMX (1,3,5,7-tetranitro-1,3,5,7-tetrazocane) guided by molecular dynamics: Pore collapse, shear bands, and hotspot temperature

Meso-scale calculations of energy localization and initiation in energetic material microstructures must capture the deformation and collapse of pores and high-temperature shear bands, which lead to hotspots. Because chemical reaction rates depend sensitively on temperature, predictive continuum models need to get the pore-collapse dynamics and resulting hotspot temperatures right; this imposes stringent demands on the fidelity of thermophysical model forms and parameters and on the numerical methods employed to perform high-resolution meso-scale calculations. Here, continuum material models for β-HMX are examined in the context of shock-induced pore collapse, treating predictions from all-atom molecular dynamics (MD) simulations as ground truth. Using atomistics-consistent material properties, we show that the currently available strength models for HMX fail to correctly capture pore collapse and hotspot temperatures. Insights from MD are then employed to advance a Modified Johnson–Cook (M-JC) strength model, which is shown to capture key aspects of the physics of shock-induced localization in HMX. The study culminates in a MD-guided strength model for β-HMX that produces continuum pore-collapse results in better alignment on several aspects with those predicted by MD, including pore-collapse mechanism and rate, shear-band formation in the collapse zone, and temperature, strain, and stress fields in the hotspot zone and the surrounding material. The resulting MD-informed/MD-determined M-JC model should improve the fidelity of meso-scale simulations to predict the detonation initiation of HMX-based energetic materials in microstructure-aware multi-scale frameworks.

High-dose vitamin C as a metabolic treatment of cancer: a new dimension in the era of adjuvant and intensive therapy.

The anti-cancer mechanism of High-dose Vitamin C (HDVC) is mainly to participate in the Fenton reaction, hydroxylation reaction, and epigenetic modification, which leads to the energy crisis, metabolic collapse, and severe peroxidation stress that results in the proliferation inhibition or death of cancer cells. However, the mainstream view is that HDVC does not significantly improve cancer treatment outcomes. In clinical work and scientific research, we found that some drugs or therapies can significantly improve the anti-cancer effects of HDVC, such as PD-1 inhibitors that can increase the anti-cancer effects of cancerous HDVC by nearly three times. Here, the adjuvant and intensive therapy and synergistic mechanisms including HDVC combined applicationof chemoradiotherapies multi-vitamins, targeted drugs, immunotherapies, and oncolytic virus are discussed in detail. Adjuvant and intensive therapy of HDVC can significantly improve the therapeutic effect of HDVC in the metabolic treatment of cancer, but more clinical evidence is needed to support its clinical application.

Fabrication and in-plane compressive collapse of CFRP honeycomb metamaterials

A pin-slot positioning method was proposed to fabricate carbon fiber reinforced polymer (CFRP) metamaterials of hexagonal and zero Poisson’s ratio semi-re-entrant honeycombs with the same mass of monolayer continuous twill-woven carbon fiber/epoxy prepregs. The in-plane compressive collapse of CFRP honeycombs was explored through experiments and finite element (FE) simulations. Furthermore, analytical models were developed to predict the modulus and initial collapse stress of the hexagonal and semi-re-entrant honeycombs. Good agreement is achieved between analytical predictions, FE simulations and experimental results. It is shown that the initial collapse of CFRP honeycombs is by the bending of cell walls. Once initial collapse has been attained, both hexagonal and semi-re-entrant honeycombs have a stress softening. The collapse and failure modes of CFRP honeycombs strongly depend on cellular configurations and loading directions.

Dexmedetomidine and argon in combination against ferroptosis through tackling TXNIP-mediated oxidative stress in DCD porcine livers

Graft availability from donation after circulatory death (DCD) is significantly limited by ischaemia reperfusion (IR) injury. Effective strategies to mitigate IR injury in DCD grafts are essential to improve graft quality and expand the donor pool. In this study, liver grafts from DCD pigs were preserved in the University of Wisconsin (UW) solution saturated with 0.1 nM dexmedetomidine (Dex) and various concentrations of noble gases Argon (Ar) and/or Xenon (Xe) at 4 °C for 24 or 72 h. The combined 50% Ar and Dex provided maximum protection to liver grafts by reducing morphological damage, apoptosis, necroptosis, ferroptosis, hepatocyte glycogen depletion, reticulin framework collapse, iron deposition, and oxidative stress. In vitro, human liver Hep G2 cells were preserved in the UW solution saturated with 0.1 nM Dex and 50% Ar in combination at 4 °C for 24 h, followed by recovery in medium at 37 °C for up to 48 h to mimic clinical IR injury. This treatment significantly increased the expression of anti-oxidative stress proteins by promoting the translocation of thioredoxin-interacting protein (TXNIP) to mitochondria, thereby inhibiting ferroptosis, increasing plasma membrane integrity, and maintaining cell viability.In summary, The combination of 0.1 nM Dex and 50% Ar may be a promising strategy to reduce ferroptosis and other form cell death, and preserve liver grafts.

Black radish root extract alleviates sodium valproate-induced liver damage via inhibiting mitochondrial membrane potential collapse and oxidative stress in mice

Objective: To explore the effect of black radish (Raphanus sativus L. var niger) root extract on liver enzymes, oxidative stress, and histopathological alterations in mice with sodium valproate-induced hepatotoxicity. Methods: Thirty-two mice were divided into four groups: the control group received drinking water by gavage, the second group was administered with 100 mg/kg of sodium valproate, the third group received 300 mg/kg of black radish root extract, and the fourth group was given both sodium valproate (100 mg/kg) and black radish root extract (300 mg/kg). After 28 days, the mice were euthanized, and serum levels of aspartate aminotransferase (AST), alanine aminotransferase (ALT), and alkaline phosphatase (ALP), along with liver malondialdehyde (MDA), reactive oxygen species (ROS), mitochondrial parameters, tumor necrosis factor-alpha (TNF-α) gene expression, and histopathological changes were assessed. Results: Sodium valproate caused hepatic damage in mice, characterized by elevated serum levels of liver enzymes, increased MDA and ROS levels and TNF-α gene expression, as well as histopathological alterations. The black radish root extract significantly alleviated sodium valproate-caused hepatic injury by decreasing the serum levels of ALT and AST, MDA, ROS, TNF-α gene expression, as well as mitochondrial impairment, but did not have a significant effect on sodium valproate-induced histopathological changes. Conclusions: The black radish root extract demonstrates protective effects against sodium valproate-induced liver injury, possibly through mitigating oxidative stress, mitochondrial impairment, and inflammatory mediator expression.

Achieving high strength and energy absorption of novel 3D printed helical layered square honeycombs

Bionics shape design of cellular structures has the potential advantage of improving their both mechanical properties and energy absorption capabilities to the conventional honeycomb structures. In this article, inspired by square porous wood and DNA double helix, we demonstrate the creation of the novel helical layered square honeycombs (HLSHs) that simultaneously exhibit high strength and excellent energy absorption capacity. In-plane compression experiments and finite element simulations revealed that helical structure can effectively strengthen every unit cell to resist local stress concentration which always leads to rapid strain localization and finally followed by catastrophic collapse. Furthermore, the stiffness, strength and energy absorption capability can be continuously improved by increasing the number of helical layers. More specifically, the HLSH-4L (4 layers) exhibits higher collapse stress (∼176 %) and specific absorption energy (∼502 %) compared with that of regular square honeycomb (RESH). The investigation of deformation and failure behavior show that the helical structure can supply high cell-buckling resistance and facilitate the “X” shape deformation band. Besides, the helical structure also caused the transition of failure mechanisms from printing fibers tearing in RESH to layer cracking in HLSHs. This study can present insight into the design of lighter and stronger honeycomb.

Cardiomyocyte-specific Tbk1 deletion aggravated chronic doxorubicin cardiotoxicity via inhibition of mitophagy

Doxorubicin (Dox) use is limited by Dox-induced cardiotoxicity. TANK-blinding kinase 1 (TBK1) is an important kinase involved in the regulation of mitophagy, but the role of TBK1 in cardiomyocytes in chronic Dox-induced cardiomyopathy remains unclear. Cardiomyocyte-specific Tbk1 knockout (Tbk1CKO) mice received Dox (6 mg/kg, injected intraperitoneally) once a week for 4 times, and cardiac assessment was performed 4 weeks after the final Dox injection. Adenoviruses encoding Tbk1 or containing shRNA targeting Tbk1, or a TBK1 phosphorylation inhibitor were used for overexpression or knockdown of Tbk1, or inhibit phosphorylation of TBK1 in isolated primary cardiomyocytes. Our results revealed that moderate Dox challenge decreased TBK1 phosphorylation (with no effect on TBK1 protein levels), resulting in compromised myocardial function, obvious mortality and overt interstitial fibrosis, and the effects were accentuated by Tbk1 deletion. Dox provoked mitochondrial membrane potential collapse and oxidative stress, the effects of which were exacerbated and mitigated by Tbk1 knockdown, specific inhibition of phosphorylation and overexpression, respectively. However, Tbk1 （Ser172A） overexpression did not alleviate these effects. Further scrutiny revealed that TBK1 exerted protective effects on mitochondria via SQSTM1/P62-mediated mitophagy. Tbk1 overexpression mediated cardioprotective effects on Dox-induced cardiotoxicity were cancelled off by Sqstm1/P62 knockdown. Moreover, TBK1-mitophagy-mitochondria cascade was confirmed in heart tissues from dilated cardiomyopathy patients. Taken together, our findings denoted a pivotal role of TBK1 in Dox-induced mitochondrial injury and cardiotoxicity possibly through its phosphorylation and SQSTM1/P62-mediated mitophagy.

Friction stir seam- and spot-welded aluminium honeycombs: Enhanced structural integrity eliminating adhesive bonding challenges

Aluminium honeycombs serve as a primary core material for energy absorption in various transportation and structural applications, with particular emphasis on their superior strength in the out-of-plane direction. However, conventional fabrication methods rely on adhesive bonding of aluminium strips, revealing poor bond strength under collapse stress. Premature structural failure arises from adhesive failure and subsequent debonding of cell walls, occurring before the aluminium strips fail. Addressing this, an innovative approach utilizing friction stir seam, and spot welding has been introduced to overcome adhesive bonding limitations. Welded joints exhibit a remarkable tenfold increase in strength compared to adhesive bonds. Notably, welded honeycombs demonstrate 32–37% higher crushing strength and an 80–84% increase in specific energy absorption capacity over adhesive-bonded variants. Collapse mechanisms involve pure buckling in seam-welded honeycombs without weld region failure, while spot-welded honeycombs display a combination of bending-shear and spot tearing, particularly evident with wider weld spacing. Obtaining longitudinal loading on seam-welded honeycomb walls is advantageous because of its 57% higher normalized maximum load capacity compared to the shear-tensile strength obtained for spot-welded walls. This study marks a significant advancement in the existing manufacturing route for honeycombs in achieving superior crushing performance.

On the collapse stress of tubular enhanced anti-tetra-missing rib structure

In the contemporary landscape of engineering, escalating demands for advanced material and structural performance have brought metamaterials to the forefront. Among them, the enhanced anti-tetra-missing rib structure has gained prominence owing to its auxetic behavior under significant strain. However, the lack of research on its quasi-static and dynamic mechanical performance have hindered its practical application. To address this, we introduce the tubular enhanced anti-tetra-missing rib structure (TEATMRS) and derive its collapse stress expression under various conditions. Through extensive simulations and experiments, we explore its deformation mechanisms and assess the influence of the structural geometric parameters and impact velocity on collapse stress. The results demonstrate excellent agreement among theoretical description, numerical analysis, and experimental tests, establishing the feasibility of the proposed collapse stress expression. These findings provide a theoretical foundation and design guidance for TEATMRS in engineering applications.

A closed-form structural stress-strain relation and implications on plastic design limits in codes and standards

The deformation of elastic-perfectly plastic beam or plate under combined through-thickness membrane and bending stresses (i.e., structural stress) is analyzed in this paper. Closed-form solutions of “plane-remains-plane” strain (i.e., structural strain) distribution as a function of applied stress and yield strength is derived. The relationship between structural stress and structural strain is also revealed for gaining insights on not only the plastic collapse conditions, but also through-thickness deformation behaviors leading to limit state. Based on the closed-form strain solutions, four deformation modes are identified: (1) elastic, (2) one-side yielding, (3) two-side yielding, and (4) plastic collapse. A membrane-bending stress interaction diagram is constructed to depict four zones that are associated with the four deformation modes in the normalized membrane and bending stress space. Closed-form solutions of residual stress, residual strain, and structural stress range-strain range relation after a loading-unloading cycle are also derived. Based on the parabolic plastic collapse stress limit curve, parabolic design stress limit curves with coherent safety margins for any combinations of membrane and bending stresses are constructed. The new insights gained in this study offer a more consistent definition of design stress limit than those used in the current codes and standards, e.g., ASME BP&V Code.

Effect of co on mechanical and electrochemical properties of powder synthesized cellular Ti-Al alloy

ABSTRACT This work describes the effect of Co content on the compressive and electrochemical behaviour of cellular Ti4AlxCo (x = 2%, 4%, 6% and 8 wt%) alloy. Cellular products were prepared through powder metallurgy route by adding 70 v% of ammonium bicarbonate as space holder in Ti4AlxCo powder mixture. Relative density of the final products slightly upsurged due to increment of Co amount and it was found in the range of 0.32–0.35. Microstructure represented the interconnecting pores which will be advantageous to circulate the body fluid, if used as a bone implant. Plastic collapse stress of Ti4Al8Co was about 45% higher than Ti4Al2Co. Also, the elastic modulus was under the range of modulus of natural bone (11 ± 1 GPa). In Tafel plot, value of corrosion current density shifted from 8 μA/cm2 to 15 μA/cm2 by increasing the Co content from 2 wt% to 8 wt% which indicates the hampering of corrosion resistance. Corrosion rate followed the linear relationship with Co content. Best fitted electrochemical circuit showed the double layer oxide formation during corrosion. Micrographs of corroded cellular samples also represent that the surface of material is more prone to corrosion containing higher amount of Co.

Study on re-entrant hierarchical honeycombs in-plane impact

The introduction of hierarchical structure in cell materials can further improve their energy absorption effect, and negative Poisson's ratio materials have excellent energy absorption capacity and special deformation mode. In this paper, augmented double arrow honeycomb structures is introduced into the re-entrant honeycomb with negative Poisson's ratio as a substructure (RHA) to improve the mechanical properties of the first-order re-entrant honeycomb and enhance the energy absorption effect of the structure. The analytical formula of the collapse stress of honeycomb under quasi-static compression was derived by the two-scale method. The failure stress of RHA under different relative densities and impact velocities is discussed, and the analytical formula of RHA stress in dynamic crushing is derived by combining momentum conservation. Due to the special substructure, the secondary honeycomb discussed in this paper has two plateau periods. In this paper, the second plateau stress of the honeycomb structure is calculated innovatively. The numerical simulation results show that the collapse stress of RHA in the first plateau period is similar to that of the first-order re-entrant honeycomb, and the collapse stress in the second plateau period is increased by 332%. The research in this paper shows that the honeycomb with the second plateau period has a better energy absorption effect, which is an effective strategy for improving the energy absorption effect of the honeycomb. It can be further explored to improve the impact resistance of the honeycomb.

Analysis on the collapse stress of auxetic tubular anti-tetrachiral structures

The growing demands for enhanced impact resistance in modern engineering necessitate the exploration of novel materials with superior properties. Among these materials, the tubular anti-tetrachiral structure (TATS) emerges as a promising 3D metamaterial, exhibiting exceptional characteristics owing to its auxetic effect. Nevertheless, the investigation into the collapse stress of TATSs subjected to impact remains limited. Thus, this study aims to examine the deformation modes exhibited by TATSs under both low and high velocity impacts, while also deriving the theoretical expression for collapse stress through rigorous theoretical derivations. Furthermore, we delve into the analysis of the influence exerted by impact velocity and structural geometric parameters on the collapse stress of the TATS. Sensitivity analysis is performed to identify structural geometric parameters that display heightened sensitivity, and the interplay between impact velocity and these parameters is carefully scrutinized. The findings presented in this paper furnish a robust theoretical foundation for the design and exploration of TATSs.

Characterizing a Cost-Effective Hydrogel-Based Transparent Soil.

Transparent soil (TS) was specifically designed to support root growth in the presence of air, water, and nutrients and allowed the time-resolved phenotyping of roots in vivo. Nevertheless, it is imperative to further optimize the reagent cost of TS to enable its wider utilization. We substituted the costly Phytagel obtained from Sigma with two more economical alternatives, namely Biodee and Coolaber. TS beads from each brand were prepared using 12 different polymer concentrations and seven distinct crosslinker concentrations. A comprehensive assessment encompassing transparency, mechanical characteristics, particle size, porosity, and stability of TS was undertaken. Compared to the Sigma Phytagel brand, both Biodee and Coolaber significantly reduced the transparency and collapse stress of the TS they produced. Consequently, this led to a significant reduction in the allowable width and height of the growth box, although they could still simultaneously exceed 20 cm and 19 cm. There was no notable difference in porosity and stability among the TS samples prepared using the three Phytagel brands. Therefore, it is feasible to consider replacing the Phytagel brand to reduce TS production costs. This study quantified the differences in TS produced using three Phytagel brands at different prices that will better promote the application of TS to root phenotypes.

Control of the Deformation Mode of Aluminum Foam-Filled Tubes as a Function of Foam Porosity

This paper focuses on the computational modeling of the crashworthiness performance of designed foam-filled thin-walled tubular structures under quasi-static compression loading. The studied foam sample is designed in SolidWorks using the ‘sphere subtraction method’ and implemented as a filler material in the thin-walled tube. The quasi-static compression was simulated by Abaqus software. The foam porosity is manipulated to enhance the crashworthiness performance of empty tubes. The deformation mode and energy absorption capability of the analyzed structures are introduced in detail. The numerical results showed that foam-filler material could change the deformation mode and improve stability during the compression process of thin-walled tubular structures. The number of lobes significantly increases when introducing the foam filler to the tube. These folds are affected by the foam porosity. Results also indicate that the total crushing load of the foam-filled tube is also a function of foam porosity, the mechanical response of the foam-filled tubes tended towards the response of the empty tube for a high porosity (P >85%), while for low porosity (P<85%) the mechanical response of the foam-filled tubes exhibits the three universal deformation characteristics of foams, namely, initial linear stage, extended plateau stage, and final densification stage. The main mechanical properties: collapse stress, plateau stress, and densification strain were obtained via the energy-efficient method for different configurations. The calculated mechanical properties exhibited a strong dependence on foam porosity. To give a quantitative description of the obtained quasi-static compressive properties, these properties are expressed as a function of foam porosity. The proposed formulas can easily recover the quasi-static compressive properties of the empty tube in the case of the absence of foam. The control of the compressive performance of foam-filled tubes as a function of porosity allows for finding an optimum geometry with a predefined foam porosity value adjusted for a given application.

An Investigation of Quasi-Static Compression and Shock Responses under a Pneumatic Exciter on Brittle Truss Lattice Structures Fabricated with a Vat Photopolymer Resin

Shock attenuation is a significant aspect of shockproof design. The aim of this study is to explore the use of lattice structures for shock isolation applications. Five lattice structures were fabricated using photopolymer resin and subjected to quasi-static compression tests under a universal testing machine and shock response tests under a pneumatic exciter. The quasi-static compression tests provided preliminary data on the lattice structure’s collapse modes, stress, strain, and energy absorption. The shock test results revealed that the responses from the lattice structures were complex convolutions of the frequency. Moreover, the collapsed mode under the compression experiment did not guarantee the same outcome as in the shock impulse experiment. Amongst the lattice structures, the face-centred cubic with cubic perimeter (FCC + CP) structure exhibited the poorest shock isolation properties, with an ability to absorb only approximately one-third of the shock compared to solid structures. On the other hand, the body-centred cubic with cubic perimeter (BCC + CP) structure showed the highest impulse response with average shock transmissibility, making it a viable option for applications requiring shock insulation. However, it should be noted that this data may only be applicable for high acceleration with low degrees of force, less than 300 N.

Progressive collapse and soil stress analyses of Manupali steel truss bridge in Lantapan, Bukidnon under hydraulic and traffic threats

Bridges designed to comply with current design codes may not provide enough strength to arrest a possible local failure following an abnormal event, thus leading to a progressive collapse. One may employ different approaches that vary according to linearity and dynamicity to analyze the potential of a structure to progressive collapse. Together with a prior risk assessment, this study analyzed the susceptibility of the Manupali steel truss bridge to progressive collapse using an adapted nonlinear static approach and assessed the bridge’s pile foundation capacity concerning changes in the imposed stresses caused by the dynamic effects of progressive collapse. Using P-Delta analysis in STAAD.Pro CONNECT Edition V22, this study determined that under its self-weight, the Manupali steel truss bridge is susceptible to progressive collapse, i.e., it is fracture critical. Nonetheless, being such does not mean the bridge is inherently unsafe, only that it lacks redundancy in the design. Furthermore, this study found that a collapse does not significantly detrimentally affect the foundation system except when the dynamic effect is so tremendous. With the results, this study recommends that the design of bridges should consider abnormal load cases to mitigate progressive collapse.

A Semiempirical Model for Post‐Yield Stress Instability in the Stress–Strain Response of 3D Lattice Structures under Compressive Loads

Mechanical behavior of lattice structures is important for a range of engineering applications. Herein, a new semiempirical model is proposed that describes the entire range of stress–strain response of lattice structures, including the stress‐instability region which is modeled as an oscillator. The model can be fit to individual stress–strain curves to extract elastic modulus, yield stress, collapse stress, post‐yield collapse ratio, densification strain, and the energy absorbed per unit volume. The model is fit to 119 unique experimental stress–strain curves from 13 research papers in literature covering four different lattice designs, namely, octet truss, body‐centered cubic with vertical members, body‐centered cubic, and hexagonal. Manufacturing methods (additive and conventional) and materials (metals and polymers) were also included in the analysis. The fitted model yields several new insights into the compression behavior of previously tested lattice structures and can be applied to additional lattice designs. Among other results, analysis of variance (ANOVA) reveals that the octet truss lattice demonstrates the highest post‐yield collapse ratio and the smallest normalized energy absorption per unit volume amongst the lattice structures investigated. The proposed model is a powerful tool for designers to quantitatively compare and select 3D lattice structures with the desired mechanical characteristics.

Combined effects of fault geometry and roadway cross-section shape on the collapse behaviors of twin roadways: An experimental investigation

Natural faults in key areas can significantly affect the stability of underground twin roadways. To assess the combined effect of fault geometry and roadway cross-section shape on the collapse behaviors of twin roadways, a series of uniaxial compression tests were carried out on the double-hole specimens using pre-embedded joints to represent faults. In the experiments, the digital image correlation (DIC) and acoustic emission (AE) techniques were used to monitor the strain field evolution and internal crack development in the specimens. The test results showed that the strain localization zones were mainly generated near the roadways and joint, and the initiation locations and patterns of the induced cracks were directly affected by the roadway cross-section shape and joint inclination (α). According to the collapse paths, the collapse modes of the twin roadways can be divided into three categories for different α: joint lap collapse (α = 0°), quasi-integrity collapse (α = 90°), and through-joint collapse (with α ranging from 30° to 60°). In general, the circular twin roadways were found to be more stable than the square twin roadways. Moreover, as α increased from 0° to 90°, the collapse stress was observed to first decrease to its minimum at α = 45° and then increase. Finally, the detailed stress distributions around the roadways and joint were numerically analyzed to supplement the experimental results. The results from this work can be of great engineering significance for the design and construction of similar underground roadways in jointed rock masses to achieve structural stability and safety.