Increase In Stiffness Research Articles

Small-scale physical modelling of vertically loaded, cyclically thermally-activated helical piles

To investigate the use of thermally-activated helical piles in shallow geothermal energy systems, a 1-g modelling study was conducted. Helical piles with either a single- or double- helix were installed in a medium dense, dry sand, and subjected to mechanical, thermal only and thermo-mechanical loading. The results indicate that during the thermal tests (1 – 3 cycles), a small upwards residual displacement was observed and pile head movements ranged between about 90% and 100% of the free expansion of the pile shaft above the shallowest helix, suggesting that the helices fixed the shaft and little restraint was offered by the surrounding soil. In the thermo-mechanical tests (30 thermal cycles), the pile head developed irrecoverable settlement as a function of the number of helices (more helices, less settlement) and initial load (higher load, greater settlement). No significant alteration in pile axial stiffness or resistance was found for piles with zero mechanical load that underwent only a few thermal cycles; however, an increase in stiffness and resistance, beyond that due to inherent variability in the test setup, was observed for piles with an initial load and following a large number of thermal cycles. The testing of thermally-activated helical piles in sand has confirmed that the response is similar to conventional piles and that thermal ratcheting effects can be managed by the application of suitable margins of safety in design and/or the use of multi-helix piles.

Experimental study on strengthening steel-truss bridge diagonal members using carbon-fibre-reinforced polymer bonding methods

This study investigated the effectiveness of carbon fibre-reinforced polymer (CFRP) materials in strengthening the diagonal tension members of steel-truss bridges. Monotonic tensile and cyclic loading tests were performed on CFRP-strengthened specimens with variations in the CFRP-bonding range on the flanges. This study focused on the strengthening methods A and B, which were proposed to address insufficient CFRP anchoring near gusset plates by bonding CFRP sheets to both sides of the flanges of the diagonal tension members. The results of the monotonic tensile loading tests indicated a significant increase in tensile stiffness and substantial improvements in yield strength (27%) and ultimate load-bearing capacity (51%) when the strengthening methods A and B were employed. Delamination of the bonded CFRP sheets was effectively delayed, occurring only after the steel yielded, owing to the use of a ductile adhesive (polyurea putty). On the other hand, the cyclic loading tests demonstrated a significant enhancement in the load-bearing capacities (33% for tensile, 32% for compressive) of the strengthened specimens. Moreover, the energy dissipation capacities of the specimens strengthened by methods A and B exhibited linear increases, with 12% and 14% higher values respectively than those of the non-strengthened specimen. Although the stiffnesses (tensile and compressive) of the strengthened specimens decreased in each loading loop, the strengthening methods A and B maintained the stiffness values at approximately 35% higher than those of the non-strengthened specimen.

Quantitative assessment of well leakage, part I: Cement stress evolution

A damaged cement sheath in wells can open a leakage pathway to shallow freshwater aquifers and atmosphere. Quantitative assessment of leakage along wells has become an area of interest for both the industry and the regulatory bodies. The well leakage can be of importance in both active and legacy wells. In order to estimate leakage through cement sheaths, the size of the leakage pathway and the damage in the cement sheath must be estimated. In this work, we have developed a hydro-thermo-mechanically coupled near-well model that aims to calculate the evolution of cement’s stress as it cures. This process takes into account the cement’s gradual increase in stiffness, chemical shrinkage, and the heat of hydration. The results are verified using lab measured cement stress and pore pressure data from the literature. A case study was developed based on a low-enthalpy geothermal doublet in the Netherlands. The results show that during the cold water injection, an outer microannulus may open to 60 µm. The presence of an external source of water and formation stiffness are of significant importance in determining the damage to the cement sheath. The heat of hydration in cement increases the temperature of cement during curing. The subsequent drop in temperature due to drilling or completion reduces the cement stress and exacerbates the damage to the cement sheath. The producer well may not form a microannuli, however shear and cyclical failure may be of higher likelihood. The modelling framework presented here allows for estimation of annular cement stress in the well. The analysis provides quantitative estimates of the size of the leakage pathway along a well that can be used to estimate well leakge. Quantitative estimate of well leakage provides crucial information for quantitative risk analysis and provides a framework to optimize well operations to minimize leakage risk.

Enhanced seismic performance: A novel cable brace with bending energy dissipation for semi-rigid steel frames

Ordinary braces upon experiencing compressive buckling, reach a fully plastic state, rendering them ineffective against further seismic action. Moreover, their post-earthquake repair and reinforcement pose significant challenges. Addressing these issues, this research introduces an innovative lateral force-resisting element: the bending energy dissipation-cable brace. This novel design utilizes steel cables in a unique tension-only arrangement, effectively dissipating seismic energy by inducing bending in a steel plate. A semi-rigid steel frame was constructed, incorporating two variations of the cable brace, differentiated by the thickness of their energy-dissipating frames. These were subjected to quasi-static cyclic loading tests to evaluate their hysteretic behavior, deformation pattern, load-bearing capacity decay, and energy dissipation capacity. The experimental results reveal the superior seismic performance of the bending energy dissipation-cable brace, evidenced by a 22 % enhancement in energy dissipation and a 38 % increase in stiffness when the thickness of the energy-dissipating frame is doubled. These results offer a promising solution to the current limitations in energy dissipation and difficulty of application of the combined brace of steel cable and bending yielding energy dissipation devices.

The effect of salidroside on the bone and cartilage properties in broilers

Leg disorders frequently occur in fast-growing broiler chickens, constituting severe health and welfare problems. Although salidroside (SAL) promotes osteogenesis and inhibits apoptosis of chondrocytes in rats, it remains to be determined whether SAL can effectively improve bone growth in broilers. The present study was designed to investigate the effects of dietary SAL supplementation on bone and cartilage characteristics in broiler chickens. Ninety-six Arbor Acres broiler chickens were randomly divided into 4 groups: control, low-dose SAL, medium-dose SAL, and high-dose SAL groups. The broiler chickens were raised until 42 d of age, with samples of bone and cartilage collected for biomechanical testing and bone metabolism index detection. The results showed that SAL significantly increased the vertical external diameter, cross-sectional moment of inertia, and cross-sectional area of the femur and tibia. Additionally, SAL enhanced bone mineral density and strength, as evidenced by significant increases in stiffness, Young's modulus, ultimate load, and fracture work of the femur and tibia. Furthermore, SAL influenced the relative content of phosphate, carbonate, and amide I in cortical bone. Moreover, SAL upregulated the expression of osteogenic genes (Collagen-1, RUNX2, BMP2, and ALP) in a dose-dependent manner and maintained the homeostasis of the extracellular matrix (ECM) of chondrocytes. These results indicated that SAL promoted leg health in broilers by improving bone and cartilage quality and enhancing chondrocyte activity.

Research on the critical speed of a double span rotor system based on finite element method

Abstract Double-span rotor systems are commonly used in aerospace engines and large turbines, where critical criticality is critical in their dynamic characteristics. This paper calculates the critical critical value of the rotor through the intervention matrix method and verifies it through the finite element method. The changes in the support and wheel disc were discussed and the results show that the increase in support stiffness, the reduction in wheel disc mass, and the increase in coupling stiffness will increase the critical stress of the double-span rotor. In addition, the increase in the position of the support and the installation position of the coupling will affect the critical point.

Mechanical Stiffness and Permeability of a Reservoir‐Scale Rough Fracture During Closure

AbstractWe study how the normal stiffness and the permeability of a realistic rough fracture at the field scale are linked and evolve during its closure up to the percolation threshold. We base our approach on a well‐established self‐affine geometric model for fracture roughness, which has proven to be a relevant proxy from laboratory to multi‐kilometer scales. We explore its implications for fracture apertures in reservoir‐scale open channels. We build our approach on a finite element model using the MOOSE/GOLEM framework and conduct numerical flow‐through experiments in a 256 granite reservoir hosting a single, partially sealed fracture under variable normal loading conditions and undrained conditions. Navier‐Stokes flow is solved in the embedded 3‐dimensional rough fracture, and Darcy flow is solved in the surrounding poroelastic matrix. We study the evolution of the mechanical stiffness and fluid permeability of the fracture‐rock system during fracture closure including mechanisms that impact the contact surface geometry like asperity yield and deposit of fracture‐filling material in the open space of the rough fracture. The largely observed stiffness characteristic is shown to be related to the self‐affine property of the fracture surface. A strong anisotropy of the fracture permeability is evidenced when the fluid percolation thresholds are exceeded in two orthogonal directions of the imposed pressure gradient. We propose a unifying physically based law for the evolution of stiffness and permeability in the form of an exponential increase in stiffness as permeability decreases.

Abstract P306: Aldosterone levels are associated with hypertension in post-menopausal women: the Study of Women’s Health Across the Nation

Introduction: Hypertension (HTN) is the leading cause of premature death in women. Apparent treatment-resistant hypertension (aTRH) is systolic blood pressure (SBP) ≥140 or diastolic BP (DBP) ≥90 mmHg despite treatment with ≥3 antihypertensive medications, or the use of ≥4 antihypertensive medications (irrespective of the BP level). aTRH occurs in approximately 17% of people with treated HTN. High aldosterone may elevate cardiovascular risk; despite causing sodium retention, aldosterone may paradoxically continue to be secreted even when dietary sodium intake is high. Little is known, however, about how aldosterone relates to BP and HTN in women, in whom significant increases in BP, carotid atherosclerosis, and arterial stiffness occur near the time of menopause. We examined the relationships of aldosterone with HTN and aTRH in a cohort of post-menopausal women. Methods: The Study of Women’s Health Across the Nation (SWAN) is a longitudinal cohort of women followed from midlife into late adulthood. This cross-sectional analysis included 999 women (30.3% of the cohort) free of congestive heart failure and with serum aldosterone measured during the 2015-2016 (15th follow-up) study visit. HTN was defined as SBP or DBP ≥140 or ≥90 mmHg, respectively, or use of antihypertensive medications. aTRH was defined as reported use of 4 or more concurrent antihypertensive medications at any visit, or 3 or more concurrent medications and SBP≥140 or DBP≥90 at two consecutive visits. Multivariable logistic regression related HTN or aTRH and aldosterone, adjusting for age, race/ethnicity, and body mass index. Results: In this cohort of women [mean age 66 years (standard deviation:2.7)], the prevalence of HTN and aTRH was 52% and 4.1%, respectively. Women with aTRH had higher median serum aldosterone [8.7 ng/dL, interquartile range (IQR) 5.0-11.7] versus those without (6.7 ng/dL, IQR 2.7-10.5). Each unit increase in aldosterone was associated with a 4% increased odds of HTN (95%CI 1.02,1.06; p<0.001). Similarly, the odds ratio for aTRH in the adjusted model was 1.04 (95%CI 0.99,1.08), although the association was not statistically significant (p=0.09). Conclusion: Aldosterone was positively associated with HTN and there was a non-statistically significant trend toward an association with aTRH in this cohort of post-menopausal women. Our findings suggest that aldosterone within an ostensibly “normal” range is associated with HTN in postmenopausal women.

Micromechanical investigation of the aging mechanism in sand

The current mechanisms and factors influencing soil aging remain inconclusive and incomplete. Discrete element method (DEM) is adopted to investigate the responses of irregularly shaped granular assemblies subjected to creep and post-creep triaxial shear. The simulated creep and aging behaviours are generally in line with those observed in existing laboratory tests and numerical investigations. In addition to an increase in soil stiffness, the DEM analyses predict an enhanced soil strength as a result of the prolonged interlocking between sand particles during the relatively long creep duration. It is demonstrated that the creep-induced interlocking is directly manifested as a shear resistance above the minimum energy line. The development of interlocking explains the overshooting behaviour observed in post-creep shear. The microscopic responses do not support the aging mechanism based on the buckling of strong force chains. A new hypothesis, termed ‘microstructure evolution by stability selection’, is proposed to explain soil aging. This hypothesis suggests that interlocking between particles develops naturally during the creep process because interlocked particle clusters generally have a greater chance to survive the particle rearrangement induced by creep, leading to an increased number of interlocked particle clusters in aged soils.

Abstract 14: Arterial Stiffness in Obese Normotensive Children: The First Cardiovascular Risk Biomarker?

Introduction: Obesity is an emerging pandemic driven by consumption of a diet rich in fat, highly refined carbohydrates and a sedentary lifestyle in both children and adults. In obesity arterial stiffness (AS) often associated with endotelial dysfunction (ED) is an independent and strong predictor of cardiovascular disease (CVD) and is a precursor to atherosclerosis, systolic hypertension, cardiac diastolic dysfunction, and impairment of coronary and cerebral flow. In obese children, AS also promotes fatty liver disease whitch eventually leads to fibrosis. Aim of Study: In obese children (OC), central blood pressuere, arterial stiffness and endothelial dysfunction, liver steatosis/fibrosis were evaluated and compared with control group (CG), non-obese, non-hypertensive children. Methods: Carotid-femoral pulse wave velocity (PWV) is the current non-invasive method of choice to asses AS and PWV carotid-brachial variation pre- and post-induced transient ischemia of brachial artery to evaluate ED. Fibroscan (FS) and Control Attenuation Parameter (CAP) are a non-invasive reliable examination that allows to know the degree of liver steatosis and liver stiffness (fibrosis). Carotid-femoral PWV (AS) and PWV variation of brachial artery (ED) were assessed using Complior System® (Artech-Medical France). We evaluated 31 obese children between 10 and 13 years old (BMI 28.70±3.72) and compared to CG (between 11 and 13 years old, n=16, BMI 19.89±1.75) Results: In obese children (BMI 28.70±3.72 and Z score 2.02±0.42) vs CG (BMI 19.89±0.75 and Z core 0.57±0.24), PWV-CF (arterial stiffness) was significantly increased: 5.8±1.3 m/s vs. 3.4±0.9 m/s, p<0.01. PWV-CB variation were paradogical (endothelial dysfunction) after transient ischemia in obese children (△+9% compared to baseline) and it was as epected in the CG (△-12.2% compared to baseline) (P<0.001). Fibroscan and CAP revealed that the degree of steatosis was significantly higher in OC but no differences were found in the degree of liver fibrosis. Conclusions: We found a significatly increase in arterial stiffness in obese children compared to CG. Arterial stiffness in obese children often precedes the development of hypertension and liver fibrosis (even in the presence of liver steatosis) suggesting that arterial stiffness is one of the earliest biomarkers for increased cardiovascular risk. Interventions aimed at attenuating obesity in chidhood are emerging as important target to improve public health outcomes.

An Investigation into the Impact of Time-Varying Non-Conservative Loads on the Seismic Stability of Concrete-Filled Steel-Tube Arch Bridges

When the arch rib of the mid-bearing through and lower-bearing through arch bridges undergoes out-of-plane deformation, it is usually subject to the resilience force provided by the flexible hanger, which is known as the “non-conservative force effect” of the suspender. In contrast to the static condition, in the dynamic scenario, the time-varying non-conservative force exerted by the flexible suspender becomes more complex due to dynamic changes in external load. Moreover, the difference in fundamental frequency and vibration period between the bridge system and arch rib may influence the stress distribution within the arch rib during ground motion. This paper investigates the impact of time-varying non-conservative forces on the dynamic stability of arch ribs in concrete-filled steel tube (CFST) bridges under seismic loads. Specifically, it examines the influence of different seismic waveforms, frequency disparities between bridge slabs and arch ribs, and suspender stiffness on the non-conservative effect. The results reveal significant disparities in the impact of non-conservative forces exerted by the suspender during seismic events with identical intensity but varying frequency characteristics. The influence of non-conservative forces on the dynamic stability of bridges escalates as deck stiffness increases, while it remains relatively unaffected by changes in suspender stiffness.

Variable stiffness performance analysis of layer jamming actuator based on bionic adhesive flaps

Soft actuators made of soft materials cannot generate precisely efficient output forces compared to rigid actuators. It is a promising strategy to equip soft actuators with variable stiffness modules of layer jamming mechanism, which could increase their stiffness as needed. Inspired by the gecko's the array of setae, bionic adhesive flaps with inclined micropillars are applied in layer jamming mechanism. In this paper, after the manufacturing process of the layer jamming actuator based on the bionic adhesive flaps is described, the equivalent stiffness models of the whole actuator are established in the unjammed and jammed states. And the shear adhesive force of a single micropillar is calculated based on the Kendall viscoelastic band model. The finite element simulation results of two bionic adhesive flaps show that the interlaminar shear stress and stiffness increase with the increase of pressure. The measurement of shear adhesive force show that the critical shear adhesive force of the bionic adhesive material is 3.2 times that of polyethylene terephthalate (PET) material, and exhibit the ability of anisotropic adhesion behavior. The variable stiffness performance of the layer jamming actuator based on bionic adhesive flaps is evaluated by three test methods, and the max stiffness reaches 8.027 N mm-1, which is 1.5 times higher than the stiffness of the layer jamming actuator based on the PET flaps. All results of simulation and experiment effectively verify the validity and superiority of applying the bionic adhesive flaps to the layer jamming mechanism to enhance the stiffness.

Arterial stiffness and genetic polymorphism of some cytokines in normotensive patients with ankylosing spondylitis

Aim of the study was to identify the incidence of arterial stiffness in normotensive patients with ankylosing spondylitis (AS) in the Trans-Baikal region, to study polymorphism of genes for some cytokines and prognostic factors for increased arterial stiffness in this disease. Material and methods. We examined 100 patients with AS, natives of the Transbaikal region, HLA-В27 positive and 100 healthy controls, HLA-B27 negative; all included in the study were Caucasian. Arterial hypertension was an exclusion criterion. Determination of single nucleotide polymorphisms of the genes IL1B (‒31T/C, rs1143627), IL10 (‒592C/A, rs1800872), IL10 (‒819C/T, rs1800871), TNF (‒308G/A, rs1800629) was carried out in all patients with AS and healthy individuals. 74 patients with AS and 40 patients in the control group underwent applanation tonometry using SphygmoCor (AtCor Medical, Australia). Results. Pulse wave velocity on the carotid-femoral segment in patients with AS was 6.5 [4.1; 11.7] m/s, in the control group – 5.2 [3.9; 7.0] m/s (p = 0.0001). In 18 patients with AS (24.32 %) it was more than the age norm, these patients made up the group with elevated arterial stiffness. In patients with AS, carriage of the homozygous AA genotype of the IL10 gene (rs1800872, ‒592C/A) was 2.18 times more common, the homozygous GG genotype of the TNF gene (rs1800629, ‒308G/A) was 1.23 times more common, and the heterozygous ST genotype of the IL10 gene (rs1800871, ‒819C/T) was 1.5 times more common than in the control group. Prognostic factors for increased arterial stiffness in patients with AS were carriage of the IL10 rs1800871 polymorphism, age, and the radiological stage of changes in the sacroiliac joints. Conclusions. Increased arterial stiffness was detected in 24.3 % of normotensive patients with AS. The CT genotype of the IL10 gene (rs1800871, ‒819C/T), AA genotype of the of the IL10 gene (rs1800872, ‒592C/A), the G allele and the GG genotype of the TNF gene (rs1800629, позиция ‒308G/A) are associated with the development of AS in Caucasians. Multivariate regression analysis identified clinical and genetic factors that predict an increase in arterial stiffness in patients with AS, natives of the Trans-Baikal Territory.

Multiparametric liver assessment in patients successfully treated for hepatitis C: a 4-year follow-up

Background Hepatitis C virus (HCV) is a major cause of chronic liver disease, in which liver stiffness increases. Liver stiffness measurements (LSM) are therefore essential in diagnosing liver diseases and predicting disease development. The study objective was to perform a comprehensive prospective assessment of the liver before, after and 4 years after treatment for HCV, including an assessment of the long-term outcome of fibrosis, steatosis and inflammation. Methods and findings Patients eligible for HCV treatment were included prospectively in 2018 (n = 47). Liver stiffness was measured using transient elastography and 2D shear-wave elastography (SWE). Blood tests, B-mode ultrasound (US) and SWE, were performed before, after (end of treatment [EOT]), 3 months after (EOT3) and 4 years after treatment (4Y). At the final visit, we added attenuation imaging and shear-wave dispersion slope (SWDS) measurements to assess steatosis and inflammation. Three months after treatment, the sustained virologic response rate was 93%. The median liver stiffness for baseline, EOT, EOT3 and 4Y was 8.1, 5.9, 5.6 and 6.3 kPa, respectively. There was a significant reduction in liver stiffness from baseline to EOT, and from EOT to EOT3. After 4 years, the mean attenuation coefficient (AC) was 0.58 dB/cm/MHz, and the mean SWDS value was 14.3 (m/s)/kHz. Conclusion The treatment for HCV was highly effective. Measurements of liver stiffness decreased significantly after treatment and remained low after 4 years. AC measurements indicated low levels of liver steatosis. Shear-wave dispersion values indicated inflammation of the liver, but the clinical implication is undetermined and should be explored in larger studies. Clinicaltrials.gov: NCT03434470 Abbreviations AC: attenuation coefficient; APRI: aspartate aminotransferase to platelet ratio index; ATI: attenuation imaging; cACLD: compensated advanced chronic liver disease; CAP: controlled attenuation parameter; FIB-4: Fibrosis-4 Index for liver fibrosis; HCC: hepatocellular carcinoma; LSM: liver stiffness measurement; NAFLD: non-alcoholic fatty liver disease; NASH: non-alcoholic steatohepatitis; SWDS: shear-wave dispersion slope; SWE: shear-wave elastography; US: ultrasound

Hydroxyapatite functionalized natural fiber‐reinforced composites: Interfacial modification and additive manufacturing

AbstractNatural fibers are lightweight, cost‐effective, readily available, and eco‐friendly materials. However, natural fiber‐reinforced composites are constrained by biological inconsistency and inferior fiber‐matrix interfacial properties, which restrict effective processing using advanced additive manufacturing methods. In this study, we develop a novel concept for natural fiber composite interfaces by growing hydroxyapatite (HAP) nanocrystals on jute fibers. The resulting hybrid composite is characterized using mechanical testing, nanoindentation, and modulus mapping. The interfacial region suggests a 31.4% increase in stiffness and possesses a storage modulus of up to 7.5 GPa. The tensile modulus and strength of the hybrid composite improves by 30% and 33%, respectively. Furthermore, we develop a novel process for the additive manufacturing of jute fiber thermoset composites through a direct writing (DW) process. The HAP modification increases thermal conductivity, consequently improving the curing process during DW and enhancing composite manufacturability. We demonstrate that the DW process enables the printing of intricate multilayer geometries with varying fiber content.Highlights Hydroxyapatite is used for natural fiber composite interfacial modification. Nanoindentation shows the interfacial region exhibits 31.4% higher stiffness. Modified composites possess superior mechanical performance. Jute fibers are thermally functionalized for composite additive manufacturing. A direct writing method is developed for continuous functionalized jute fiber.

A hyper-viscoelastic uniaxial characterization of collagenous embolus analogs in acute ischemic stroke

PurposeAcute ischemic stroke is a leading cause of death and morbidity worldwide. Despite advances in medical technology, nearly 30% of strokes result in incomplete vessel recanalization. Recent studies have demonstrated that clot composition correlates with success rates of mechanical thrombectomy procedures. To understand clot behavior during thrombectomy, which exerts considerable strains on thrombi, in vitro studies must characterize the rate-dependent high-strain behavior of embolus analogs (EAs) with different formation conditions, which can be used to fit models of hyper-viscoelasticity. MethodsIn this study, the effect of collagen infiltration as a carotid-induced collagen-rich thrombosis surrogate is considered as a contributor to embolus analog high-strain stiffness, when compared to 40% hematocrit EAs. ResultsEA high-strain stiffnesses, characterized on a uniaxial load frame, increase by an order of magnitude for collagenous clot analogs. Chandler loop analogs show high-strain stiffnesses and clot compositions commensurate with previous reports of stroke patient clots, and collagenous clots show significant increase in stiffness when compared to stroke patient clots. Finally, hyper-viscoelastic curve fitting demonstrates the asymmetry between tension and compression. Nonlinear, rate-dependent models that consider clot-stiffening behavior match the high strain stiffness of clots fairly well. Furthermore, we demonstrate that the stability of the elastic energy needs to be considered to obtain optimal curve fits for high-strain, rate dependent data. ConclusionThis study provides a framework for the development of dynamically formed EAs that mimic the mechanical and structural properties of in vivo clots and provides parameters for numerical simulation of clot behavior with hyper-viscoelastic models.

Tensile properties and damage behaviors of the prepreg-RTM co-cured composite bolted T-joint with a novel configuration

The tensile properties and damage behaviors of prepreg-resin transfer molding (RTM) co-cured composite bolted T-joints, consisting of an internal skeleton and an external skin, were investigated through experimental and numerical methods. With the validated finite element model, the effects of adding load-carrying beams, the corner radius and the stacking sequence were investigated. Results indicate that the novel T-joint, weighing only 55.7% of an equivalent sized 2A12 aluminum T-joint, can achieve 82% of the aluminum T-joint’s tensile stiffness and 107% of its proportional limit load. Damage in the joint initiates near the bolt holes and leads to delamination failure within the skeleton. With load-carrying beams including bolt holes, the tensile stiffness and ultimate load increase to 1.11 and 1.51 times that of the original configuration, respectively, with the final failure mode shifting to the fracture of the base panel. With the final failure mode unchanged, the ultimate load remains essentially unchanged with increasing the corner radius. Under tensile loads, the preferred stacking sequence for the skeleton is [0/+45/90/−45]nS. For the skin, the greater the number of ±45° plies, the higher the ultimate load, while the greater the number of 90° plies, the higher the tensile stiffness.

Design and additive manufacturing of novel hybrid lattice metamaterial for enhanced energy absorption and structural stability

In this work, a novel dual-phase metamaterial, named as “hybrid lattice metamaterial (HLM),” are designed and fabricated by combining reentrant and sea-urchin (SU) based surface-lattice (SL) structure with polyamide12 (PA12) material via material extrusion (MEX) process. Four different designs with varying reentrant truss thicknesses of 0.8 mm (H1), 1.0 mm (H2), 1.2 mm (H3), and 1.5 mm (H4) have been modified to assemble seamlessly with the empty spaces within the SL structure. Quasistatic compression tests were conducted to evaluate the deformation modes and compression characteristics. The findings from quasistatic experiments were subsequently validated using numerical simulations. The H4 metamaterial exhibited superior structural properties, with 42 % increase in stiffness and 35 % enhancement in specific energy absorption compared to only SL structure. Additionally, dynamic sinusoidal compression tests were conducted to evaluate the dynamic elastic ratio (DER), hysteresis work and viscoelastic properties using the tan δ. The H4 metamaterial outperformed the SL in all dynamic properties, with a 50 % increase in elastic modulus and 36 % increase in hysteresis work. This study shows metamaterial properties can be tailored for specific requirements. SL structure facilitate elastic recovery, while H4 metamaterials offer superior energy absorption and stability, making it well-suited for protective equipment and impact-resistant components.

Fatigue life prediction of cracked cross beam of mining linear vibrating screen under cyclic load

The cross beam of a mining linear vibrating screen is prone to cracking under long-term cyclic load. In order to accurately predict the fatigue life of the cracked cross beam, a coupled analysis method of vibration and crack propagation is proposed. A 2D dynamic model of the vibrating screen is established based on the finite element method, which is verified by the vibration test platform. The cracked Euler beam element is used to model the cracked cross beam. The effects of crack depth, amplitude of excitation force, frequency of excitation force, and crack location on the crack-tip stress intensity factor of the cracked cross beam are investigated in detail. In addition, an iterative method is proposed on the basis of the Paris model. The residual service life of the beam under different frequencies of excitation force, amplitudes of excitation force, spring stiffness, crack positions, and degrees of stiffness imbalance are discussed. The results demonstrate that the fatigue life of the beam increases as the frequency of excitation force and spring stiffness increase. The increase of the amplitude of excitation force and spring permanent deformation reduces the fatigue life. The conclusion obtained provide some theoretical guidance for the design and routine maintenance of mining linear vibrating screens.

Compressive testing and modelling of additively manufactured stainless steel equal angle sections with stiffening wave patterns

Traditional structural steel manufacturing routes typically produce prismatic members comprising of flat plate elements. Under compressive actions, the capacity of these sections is often dominated by plate instability of the lowest buckling mode. The current study involves compressive testing of 6 different configurations of non-prismatic stub columns, comprising of pre-defined surface waves tested at 3 different slendernesses and 3 amplitudes including control prismatic sections. Absolute and normalised load-displacement curves are generated to compare against the control sections and assess the potential increase in strength and stiffness, and the samples’ weights are measured to evaluate the relationship between material use and strength when using this method of strengthening. Tensile coupon tests are also carried out on coupons printed from the same material to define material parameters, and an extensive parametric study is undertaken with numerical modelling software. The best case evaluated in this study indicated a strength gain of 89.9 % over a control section with an equal volume of used material. Eurocode-compatible buckling characterisation curves are then provided for two of the best performing sections. This study highlights the possibilities of this technology, paving the way towards unprecedented efficiency in future steel construction.