High Initial Peak Research Articles

Energy absorption of the kirigami-inspired pyramid foldcore sandwich structures under low-velocity impact

Foldcore sandwich structures offer a promising alternative to conventional honeycomb sandwiches in the field of lightweight structures, demonstrating significant potential as efficient energy absorption devices. The dynamic behavior of foldcore sandwich structures is crucial in response to low-velocity impacts in various engineering scenarios such as bird strikes, airdrops, and vehicle collisions. This study investigates the dynamic responses of a kirigami-inspired pyramid foldcore sandwich subjected to low-velocity impacts, which has previously exhibited remarkable energy absorption efficiency under quasi-static compression. Through a combination of experimental investigations and numerical simulations under impact conditions, it is observed that the pyramid foldcore initially undergoes pronounced localized deformation which results in a sensitivity to the loading rate and causes the high initial peak stress. Different from the mechanism observed under quasi-static compression, additional stationary plastic hinges on the facets are triggered during the post-buckling stage, thereby slightly enhancing the overall energy absorption. Moreover, the multi-layer pyramid foldcores with graded geometries are proposed, characterized by varying height and wall thickness for each layer. The graded pyramid foldcores significantly reduce the initial peak stress while maintaining energy absorption efficiency. In comparison with the conventional square honeycomb and Miura-ori foldcore under the impact velocity of 10 m/s, the uniformity ratio of the graded pyramid foldcore decreases by 70.9 % and 80.5 %, while the specific energy absorption improves by 0.97 % and 138.37 %, respectively. To summarize, the graded pyramid foldcore shows outstanding energy absorption efficiency, indicating its potential as a high-performance sandwich structure for impact applications.

Numerical and theoretical analysis of the out-of-plane crushing behavior of a sinusoidal-shaped honeycomb structure with tunable mechanical properties

Honeycomb structures are widely utilized for energy absorption in engineering, showing superior crushing strength and energy absorption in the vertical direction, yet their potential as energy absorbers is limited due to a high initial peak force (IPF) in that direction. In this study, a novel honeycomb structure with tunable out-of-plane mechanical properties is developed by incorporating sinusoidal-shaped features into traditional vertically straight-walled cells. Crushing behavior and energy absorption performance of sinusoidal-shaped honeycomb structure (SSHS) under quasi-static out-of-plane compression are investigated numerically and theoretically. Results demonstrate that the IPF and the fluctuation of crushing response of SSHS can be effectively reduced for the introduction of sinusoidal-curved configuration. The predictable collapse mode of SSHS could be achieved for the buckling-induced features of trough and peak of sinusoidal waves. Parametric analyses were carried out to explore the influence of the geometrical topology of sinusoidal waves, namely, wave amplitude (A = 0.6–1.6 mm), wave number (N = 1–6) and the relative density (ρ = 0.05–0.25) on the out-of-plane mechanical properties of SSHS, including IPF, mean crushing force (MCF), specific energy absorption (SEA) and crushing force efficiency (CFE). The results imply properly adjusting topology parameters can determine the collapse patterns and the stress distribution, thereby substantially improving the mechanical properties. Moreover, theoretical investigation was also performed based on the simplified super folding element theory. The calculation of MCF shows a good agreement between the theoretical predictions and the numerical results. The sinusoidally curved-walled topology design strategy provides insights into the development of lightweight structures with controllable and improved crushing performance.

Thermal cycle induced solid-state phase evolution in IN718 during additive manufacturing: A physical simulation study

Additive manufacturing (AM) is well-known for its capability to produce and repair intricate parts e.g., Ni-based superalloy components used in aero-engine applications. However, a comprehensive understanding of the microstructure evolution and its link to properties remains elusive, with gaps in the through-process evolution of γ grains, γ', γ'', δ, and other phases in response to thermal cycling. The outstanding challenge here is to observe these transformations dynamically during the 3D printing process, as this usually requires complex in-situ measurements. Here we apply a different approach to systematically reveal the impact of thermal cycling on the solid-state microstructure evolution of IN718, via a combination of physical simulations and thermo-kinetic modelling.We replicate the thermal cycles IN718 experiences during laser directed energy deposition. Solid-state thermal cycles are shown to have minor effects on the grain morphology due to short holding times at critical temperatures, however, they do induce plastic strain accumulation. Significantly, we show how thermal cycling influences the evolution of γ', γ", and δ phases. While high initial peak temperatures inhibit the precipitation of γ', γ", and δ phases, prolonged thermal cycling to gradually decreasing peak temperatures promotes their precipitation. The δ phase forms along grain and twin boundaries, while both γ' and γ" predominantly precipitate in Nb-enriched regions, causing heterogeneities in hardness. Our results underpin the suitability of physical simulations for replicating superalloy AM, highlighting its potential as a tool to advance the current limited understanding of the microstructure and property evolution.

Dynamic crushing and energy absorption of bio-inspired shear thickening fluid-filled origami metastructure

In this study, a novel approach is proposed to enhance the crushing efficiency and energy-absorbing performance of origami metastructure by incorporating the shear thickening fluid (STF), which mimics the existence of the viscoelastic material found inside the protective mechanism in nature. The dynamic crushing and energy-absorbing performances of the proposed STF-filled origami metastructure are numerically investigated using the commercial software LS-DYNA. A fluid-structure interaction (FSI) technique is employed to simulate the coupling between the structure parts and the infilled fluid. The crushing performances of the proposed STF-filled origami metastructure (STF-OM) are investigated and compared with the non-filled and viscous fluid-filled counterparts under various crushing velocities. The effects of the filled height of STF, the viscosity of STF, and the origami folding angle on the crushing performances of STF-OM are also investigated. It is found that the proposed STF-OM can generate a higher and more steady crushing force without inducing a significantly high initial peak force. Its crushing resistance and energy-absorbing capability increase with the increase in crushing velocity, demonstrating its adaptive crushing performance for various impact scenarios. The filled height and viscosity of STF, as well as the origami folding angle, significantly affect the energy-absorbing efficiency and crushing performance of the proposed structure.

Energy absorption characteristics of thin-walled tube filled with liquid suspension of hollow glass microspheres under axial crushing

The deviation between the high initial peak force and low mean crushing force of thin-walled tubes has significantly limited its energy absorption efficiency. To tackle this challenge, a liquid suspension of hollow glass microsphere (SHGM) is employed as a new type of filling material. The axial crushing behavior of SHGM-filled tubes is evaluated by a series of quasi-static compression and dynamic drop weight impact tests. Results show that the specific energy absorption of the composite tube is increased more than 40 %. The energy absorption efficiency of SHGM-filled tube is increased to 0.65–0.70 compared to that of empty tube (0.37–0.43). This promoted energy absorption performance of the composite tube is due to the much-enhanced SHGM liquid filler-tube wall interaction, which is validated from the increased strengthening coefficient of 4.0. This enhanced filler-tube wall interaction is visualized by using 3D digital image correlation technique. These results demonstrate that the SHGM is a superior filling material for thin-walled structures and facilitate the design of next generation lightweight composite structures for energy absorption purposes.

The design of circular tubes with stepped varying thicknesses and their synergistic multi-tube combination

A stepped wall circular tube with varying thickness (STVT) and its multi-tube synergistic combination energy absorption structure were developed to address the shortcomings of the high initial peak force of thin-walled metal tubes and the significant load fluctuation of conventional multi-tube combination structures. The STVT was designed with different thickness variations, and its crashworthiness was evaluated numerically and experimentally. An analysis was done on the influences of various characteristics, such as the number of steps and thickness variation, on the crashworthiness of STVTs. Research shows that the STVT with three and four steps has improved crashworthiness. The phase of the curve is significantly influenced by the initial thickness, and for each 0.6 mm difference in step thickness, the peak phase shifts by about 5.5%. In comparison to the combination of four equal-thickness tubes of the same mass, the optimal combination structure optimizes smoothness by 10.67%, energy absorption by 19.52%, crushing force efficiency by 15.30%, and initial crushing force by 20.70%.

Crushing analysis of hierarchical multicellular tubes with gradient character along axial and radial directions under oblique loads

To overcome the disadvantage of high initial peak crush force (IPCF) in hierarchical and gradient structures, the hierarchical multicellular tubes (HMTs) with gradient character along axial and radial directions are proposed based on the bidirectional structural characters of bamboo stem. Crashworthiness performances of HMTs under oblique loads are systematically studied by using numerical simulation. Results show that compared with the square tube with the same mass, HMTs have higher energy absorption capability under different impact angles. The maximum increases of specific energy absorption (SEA) and crush force efficiency (CFE) reach up to 67.02% and 806%, respectively. Whereas, the maximum decrease of IPCF reaches up to 79.92%. Effects of structural parameters, including hierarchical level, wall thickness and internode space, on the crashworthiness performances of HMTs are also fully investigated.

Dynamic crushing performance of bio-inspired sandwich structures with beetle forewing cores

A novel design of Sandwich Structure inspired by Beetle Forewing (SSBF) is proposed in this study by mimicking the internal structure of beetle forewing. The viscoelastic material and the arch shape of hollow cavity structures found inside the forewing structure of the beetle are imitated by utilising the shear thickening fluid (STF) and semi-arch cores, respectively. The coupling interaction between fluid and structural components is analysed using a fluid-structure interaction (FSI) technique in LS-DYNA. It is found that the proposed SSBF by partially filling the core with STF generates a higher mean crushing force and stabilises the crushing force-displacement profile without a noticeably high initial peak crushing force as compared with the empty, polyurethane (PU) foam-filled, or Newtonian viscous fluid-filled counterparts. Furthermore, this stable crushing force of SSBF enhances with the increase of crushing speed, showing ideal behaviour for energy absorption and crushing resistance for the adaptation to the design of structures to resist impact loads.

Improving the crashworthiness of circular tube energy absorber by introducing different Gaussian curvatures on surface

Thin-walled tubes are widely used as energy absorbers in automobile vehicles to protect the occupants during a collision. Unfortunately, too high detrimental initial peak force (IPF) generated while tube crushing causes high risk and damage to the vehicle occupants. Hence, the design of such a device is vital for achieving high energy absorption (EA) with reduced peak force. Introducing a Gaussian curvature on the tube’s wall is an efficient technique to minimize the initial peak crush force. In this connection, a new structural design solution for cylindrical tubes with different Gaussian profiles (Zero, Positive, and Negative) has been proposed to improve energy absorption characteristics with reduced peak crush force. Initially, zero Gaussian curvature tubes (simple cylindrical tubes) are numerically analyzed and validated through experimental findings to prove the efficiency of the proposed numerical model. Subsequently, positive and negative Gaussian curved tubes were analyzed numerically. Their IPCF and EA were evaluated and compared. IPCF of positive and negative curvature tubes was reduced by 20–50% and 5–10%, respectively compared to zero curvature tubes. Since the proposed tube structures are of considerable potential, they can be employed as protective systems in place of conventional tubes in vehicles.

Static and dynamic properties of a perforated metallic auxetic metamaterial with tunable stiffness and energy absorption

Auxetic metamaterials have attracted increasing attention due to their exceptional mechanical properties. However, the critical parameters of mechanical response and Poisson's ratio would be changed simultaneously when a geometrical parameter is tuned, which is adverse to achieving the quantitative design of energy absorption by tuning a single geometrical parameter. Thus, the methodology based on tuning densification strain is proposed to design auxetic unit cells with tunable stiffness. In this study, the static performance of 2D metallic auxetic metamaterials designed by the variable stiffness factor (VSF) method is examined experimentally and numerically. To further achieve tunable energy absorption under crushing load, the concept of VSF is extended to variable energy factor (VEF). The dynamic response of verified numerical models is investigated subjected to low-, medium-, and high-velocity crushing. Finally, a functionally graded auxetic structure with different design layers is proposed to effectively solve the issues of high stiffness ratio and initial peak force. These results show that the designed structure has the actual VSF and VEF percentages close to the designed value under low- and medium-velocity crushing. The findings from this study are useful for wider applications of auxetics in protective engineering.

In-Plane Strain Measurement in Composite Structures with Fiber Bragg Grating Written in Side-Hole Elliptical Core Optical Fiber.

In this paper, the application of a fiber Bragg grating written in a highly birefringent side-hole elliptical core optical fiber for two-axial strain measurement is presented. Hybrid optical fiber structures achieved by combining large side-holes and elliptical core result in a very high birefringence of 1 × 10−3 and thus high initial Bragg peak spectral separation of 1.16 nm, as well as a very high transverse force sensitivity, of up to 650 pm/(N/mm) or even −1150 pm/(N/mm), depending on the fiber orientation with respect to the applied force. Due to the ~22 %m/m GeO2 concentration in the core the fiber being highly photosensitive, which significantly simplifies FBG fabrication by UV illumination without the need for prior hydrogen loading, which worsens thermal stability. Finally, the developed FBGs written in the highly birefringent side-hole elliptical core optical fiber were embedded in the square composite plates and applied for strain measurements. Tests of two-directional four-point bending have shown usability of such FBG for two-axial in-plane strain measurement with a single FBG in iso-thermal conditions.

Two-step crystal nucleation kinetics: Solution of the master equation

The master equation of two-step nucleation is numerically solved with parameters characterizing isothermal homogeneous nucleation of ice crystals and water droplets in steam below the water freezing temperature. The time dependences of the crystal and droplet size distributions and nucleation rates as well as of the nucleation rate of ice crystals in the droplets are determined at different constant supersaturations. The stationary values of these nucleation rates are obtained in a wide supersaturation range. It is found that when the crystallization of the water droplets is slower than their growth, the stationary rate of two-step crystal nucleation is orders of magnitude lower than the corresponding stationary rate of one-step crystal nucleation. As to the stationary nucleation rate of the water droplets, it is practically unaffected by the ice crystals nucleating and growing in both the droplets and the steam. Finally, the delay times of the different nucleation processes are determined and it is found that at both low and high supersaturations the delay time of the two-step crystal nucleation is negative because of the presence of high initial peak in the nonstationary rate of this process. The results obtained provide unprecedented mechanistic insight into the kinetics of two-step crystal nucleation.

Immunogenicity of full-length P. vivax rPvs48/45 protein formulations in BALB/c mice

BackgroundPvs48/45 is a Plasmodium vivax gametocyte surface protein involved in the parasite fertilization process. Previous studies showed that Pvs48/45 proteins expressed in Escherichia coli (E. coli) and Chinese hamster ovary (CHO) cells were highly immunoreactive with sera from malaria-endemic areas and highly immunogenic in animal models. Here the immunogenicity in mice of three different vaccine formulations was compared. MethodsRecombinant (r) Pvs48/45 proteins were expressed in E. coli and CHO, purified, formulated in Alhydrogel, GLA-SE and Montanide ISA-51 adjuvants and used to immunize BALB/c mice. Animals were immunized on days 0, 20 and 40, and serum samples were collected for serological analyses of specific antibody responses using ELISA and immunofluorescence (IFAT). Additionally, ex-vivo transmission-reducing activity (TRA) of sera on P. vivax gametocyte-infected human blood fed to Anopheles albimanus in direct membrane feeding assays (DMFA) was evaluated. ResultsMost immunized animals seroconverted after the first immunization, and some developed antibody peaks of 106 with all adjuvants. However, the three adjuvant formulations induced different antibody responses and TRA efficacy. While GLA-SE formulations of both proteins induced similar antibody profiles, Montanide ISA-51 formulations resulted in higher and longer-lasting antibody titers with CHO-rPvs48/45 than with the E. coli formulation. Although the CHO protein formulated in Alhydrogel generated a high initial antibody peak, antibody responses to both proteins rapidly waned. Likewise, anti-Pvs48/45 antibodies displayed differential recognition of the parasite proteins in IFAT and ex vivo blockade of parasite transmission to mosquitoes. The CHO-rPvs48/45 formulated in Montanide ISA-51 induced the most effective ex vivo parasite blockage. ConclusionsThree out of six vaccine formulations elicited antibodies with ex vivo TRA. The CHO-rPvs48/45 Montanide ISA-51 formulation induced the most stable antibody response, recognizing the native protein and the most robust ex vivo TRA. These results encourage further testing of the vaccine potential of this protein.

Reversed-Torsion-Type Crush Energy Absorption Structure and Its Inexpensive Partial-Heating Torsion Manufacturing Method Based on Origami Engineering

Abstract Current vehicle energy absorbers face two problems during a collision in that there is only a 70% collapse in length and there is a high initial peak load. These problems arise because the presently used energy-absorbing column has no deployment shrinkage function. It has been shown that a column called the Reversed Spiral Origami Structure (RSO) developed by Nojima solves the above two problems. However, in the case of the existing technology of the RSO, the forming cost of hydroforming is too expensive for application to a real vehicle structure. Therefore, a new structure imitating RSO, named the Reversed Torsion Origami Structure (RTO), has been developed, which has excellent energy absorption in simulation. Here, a manufacturing system is developed for the RTO cheaply. Excellent results are obtained also in a physical experiment. The RTO can replace conventional energy absorbers and is expected to be widely used in not only automobile structures but also building structures.

Experimental Demonstration of Pressure-Driven Flash Boiling for Transient Two-Phase Cooling

This work demonstrates transient cooling for high-heat-flux electronics using pressure-controlled flash boiling. Many advanced electronics packages demand rapid, high-heat flux removal under stringent spatial and temporal constraints such as limited lateral heat spreading area, sharp power delivery transients, and heterogeneous power dissipation among dies. Flash cooling achieved by rapid depressurization of liquid coolant is inherently transient and provides high initial peak cooling that can be used for adaptive cooling demanded by these advanced packages. A coolant loop thermal testbed has been constructed to perform rapid transient thermo-fluid experiments of flash cooling with methanol. This work provides insights into depressurization-based flash incipience, thermodynamic analysis of flash cooling, and the ability to provide transient cooling in two application settings. First, a vapor chamber able to adapt to high initial transients applicable for short-burst applications. Second, a co-designed convective chamber that supports simultaneous power delivery and heat extraction for high-performance wafer-scale systems. A prototype vapor chamber was tested to obtain results for overall cooling and flash incipience experiments. The results demonstrate the efficacy of flash cooling for transient thermal management and highlight directions for further research and necessary data to exploit this technique for future electronics applications.

Preoperative inflammation-based scores predict early recurrence after lung cancer resection.

BackgroundInflammation in the tumor microenvironment is hypothesized to have a major role in cancer invasiveness, progression, and metastases. The purpose of this study was to evaluate the prognostic value of preoperative inflammation-based scores in terms of estimating the timing of recurrence by hazard curves in a cohort of operable, early-stage non-small cell lung cancer (NSCLC) patients.MethodsA total of 387 patients with NSCLC who underwent complete pulmonary resection from 2010 to 2019 had their C-reactive protein-to-albumin ratio (CAR), neutrophil-to-lymphocyte ratio (NLR), platelet-to-lymphocyte ratio (PLR), Glasgow prognostic score (GPS), modified GPS, systemic immune-inflammation index (SII), and advance lung cancer inflammation index (ALI) measurements taken before surgery. Hazard curves indicating changes in hazards over time were evaluated.ResultsMedian follow-up was 39.2 months. In total, 105 patients (27.1%) experienced recurrence. The resulting hazard curve with elevated CAR, SII, GPS, and mGPS, values displayed an initial high peak during the first year. Multivariate analyses showed that an elevated CAR [hazard ratio (HR), 1.987; 95% confidence interval (CI), 1.202–3.284] independently predicted the recurrence-free survival. Even in stage I disease, patients with elevated CAR and SII values showed an earlier peak of recurrence, which was about 12 to 16 months earlier than those with low values.ConclusionsEven after complete resection of stage I NSCLC, patients with elevated CAR and SII values retain a high risk of early recurrence. Preoperative inflammation-based scores can be an objective, simple, and cost-effective measurement for predicting early recurrence of NSCLC.

Perioperative ABO Blood Group Isoagglutinin Titer and the Risk of Acute Kidney Injury after ABO-Incompatible Living Donor Liver Transplantation.

For ABO-incompatible liver transplantation (ABO-i LT), therapeutic plasma exchange (TPE) is performed preoperatively to reduce the isoagglutinin titer of anti-ABO blood type antibodies. We evaluated whether perioperative high isoagglutinin titer is associated with postoperative risk of acute kidney injury (AKI). In 130 cases of ABO-i LT, we collected immunoglobulin (Ig) G and Ig M isoagglutinin titers of baseline, pre-LT, and postoperative peak values. These values were compared between the patients with and without postoperative AKI. Multivariable logistic regression analysis was used to evaluate the association between perioperative isoagglutinin titers and postoperative AKI. Clinical and graft-related outcomes were compared between high and low baseline and postoperative peak isoagglutinin groups. The incidence of AKI was 42.3%. Preoperative baseline and postoperative peak isoagglutinin titers of both Ig M and Ig G were significantly higher in the patients with AKI than those without AKI. Multivariable logistic regression analysis showed that preoperative baseline and postoperative peak Ig M isoagglutinin titers were significantly associated with the risk of AKI (baseline: odds ratio 1.06, 95% confidence interval 1.02 to 1.09; postoperative peak: odds ratio 1.08, 95% confidence interval 1.04 to 1.13). Cubic spline function curves show a positive relationship between the baseline and postoperative peak isoagglutinin titers and the risk of AKI. Clinical outcomes other than AKI were not significantly different according to the baseline and postoperative peak isoagglutinin titers. Preoperative high initial and postoperative peak Ig M isoagglutinin titers were significantly associated with the development of AKI. As the causal relationship between high isoagglutinin titers and risk of AKI is unclear, the high baseline and postoperative isoagglutinin titers could be used simply as a warning sign for the risk of AKI after liver transplantation.

Axial Crush Response of Aluminium Square Tube with Origami Patterns

Thin-walled square tubes are widely used as impact energy absorber in automotive structures due to their ease of fabrication and installation, high energy absorption capacity in terms of progressive plastic deformation and long stroke. However, the main drawback of square tube is its high initial peak force during the initial stage of crushing. An origami pattern on the faces of the tube is proposed to reduce the high initial peak force and increase the energy absorption of the tube. Static and dynamic axial crushing were performed using finite element analysis to determine the initial peak force (IPF), crush force efficiency (CFE) and plastic specific energy absorption (SEA) of tubes with origami pattern. The results of simulations were validated by experimental data. Then, various combinations of origami patterns were studied using finite element simulation only. It was found that the origami pattern significantly enhanced the tubes crush performance. Comparison between plain square tube and tubes with various origami patterns was carried out and it was found that the origami patterns reduced the initial peak force and increased the crush force efficiency for both static and dynamic loading conditions.

Surface and Interfacial Waves in a Strongly Stratified Upper Ocean

AbstractIn an idealized two-layer fluid, surface waves can generate waves at the internal interface through class-3 resonant triads in which all waves are propagating in the same direction. The triads are restricted to wavenumbers above a critical value kcrit that depends on the density ratio R between the two layers and their depths. We perform numerical simulations to analyze the evolution of a surface wave field, initially specified by a Pierson–Moskowitz-type spectrum, for R = 0.97 (representing a realistic lower a bound for oceanic stratification). At high initial steepness and peak wavenumber kp ≪ kcrit, the energy increases in the spectral tail; as a parameterization of resulting wave breaking, at each time step individual waves with a steepness greater than the limiting Stokes steepness are removed. The energy change of the surface wave field is a combination of energy transfer to the interfacial waves, spectral downshift, and wave breaking dissipation. At wavenumbers there is a net loss of energy, with the greatest dissipation at ≈1.3kp. The maximum gain occurs at ≈0.5kp. The onset of the spectral change shows a strong threshold behavior with respect to the initial wave steepness. For steep initial waves the integrated energy dissipation can reach >30% of the initial energy, and only ≈1% of the initial surface wave energy is transferred to the interfacial wave field. The spectral change could be expressed as an additional dissipation source term, and coupled ocean–wave models should include additional mixing associated with the interfacial waves and enhanced wave breaking turbulence.

Quasi-static Compressive Properties and Behavior of Single-cell Miura Origami Column Fabricated by 3D Printed PLA Material

The study of a thin-walled column structure has gained much attention due to its potential in many engineering applications, such as the crash box of a car. A thin-walled square column usually exhibits high initial peak force, which may become very dangerous to the driver or passenger. To address this issue, introducing some shape patterns, e.g., origami folding pattern, to the column may become a solution. The present work investigates the compressive properties and behavior of a square box column structure which adopts the Miura origami folding pattern. Several test pieces of single-cell Miura origami column with varying folding angle and layer height are fabricated by a 3D printer. The filament is made of Polylactic Acid (PLA), which is a brittle material. Then, compression tests are carried out to understand its compressive mechanical properties and behavior. The results show that introducing a Miura origami pattern to form a thin-walled square column can dramatically lower down the initial peak stress by 96.82% and, at the same time, increase its ductility, which eventually improves the energy absorption capacity by 61.68% despite the brittle fracture behavior.