Material Stiffness Research Articles

Rigidity‐Tunable Materials for Soft Engineering Systems

Engineering systems that leverage the flexibility and softness of soft materials have been fostering revolutionary progress and broad interest across various applications. The inherently flexible mechanical properties of these materials lay the groundwork for engineering systems that can adapt comparably to biological organisms, enabling them to adjust to unpredictable environments effectively. However, alongside the positive benefits of softness, these systems face challenges such as low durability, continuous energy demands, and compromised task performance due to the inherently low stiffness of soft materials. These limitations pose significant obstacles to the practical impact of soft engineering systems in the real world beyond innovative concepts. This review presents a strategy that employs materials with variable stiffness to balance adaptability advantages with the challenge of low rigidity. The developments are summarized in materials capable of stiffness modulation alongside their applications in electronics, robotics, and biomedical fields. This focus on stiffness modulation at the material unit level is a critical step toward enabling the practical application of soft engineering systems in real‐world scenarios.

Identification of excessive contact pressures under hand orthosis based on finite element analysis.

Implicit magnitudes and distribution of excessive contact pressures under hand orthoses hinder clinicians from precisely adjusting them to relieve the pressures. To address this, contact pressure under a hand orthosis were analysed using finite element method. This paper proposed a method to numerically predict the relatively high magnitudes and critical distribution of contact pressures under hand orthosis through finite element analysis, to identify excessive contact pressure locations. The finite element model was established consisting of the hand, orthosis and bones. The hand and bones were assumed to be homogeneous and elastic bodies, and the orthosis was considered as an isotropic and elastic shell. Two predictions were conducted by assigning either low (fat) or high (skin) material stiffness to the hand model to attain the range of pressure magnitudes. An experiment was conducted to measure contact pressures at the predicted pressure locations. Identical pressure distributions were obtained from both predictions with relatively high pressure values disseminated at 12 anatomical locations. The highest magnitude was found at the thumb metacarpophalangeal joint with the maximum pressure range from 13 to 78 KPa. The measured values were within the predicted range of pressure magnitudes. Moreover, 6 excessive contact pressure locations were identified. The proposed method was verified by the measurement results. It renders understanding of interface conditions underneath the orthosis to inform clinicians regarding orthosis design and adjustment. It could also guide the development of 3D printed or sensorised orthosis by indicating optimal locations for perforations or pressure sensors.

Effects of nanomagnesia and polypropylene-graft-maleic anhydride on the dielectric breakdown properties of polypropylene/ethylene propylene diene monomer blend

Thermoplastic polypropylene (PP) has garnered a significant attention in power cable insulation research because of its exceptional thermal tolerance and dielectric properties. Due to its poor impact strength at room temperature, PP has been blended with various elastomers, including ethylene-propylene-diene monomer (EPDM), to improve the mechanical stiffness of the final material. This, however, comes with compromised dielectric properties of the material. Recently, the addition of nanofillers to polymers has demonstrated promising properties that can be tailored for various dielectric applications, provided that nanofiller and polymer interactions are appropriately formulated. Nevertheless, the effect of nanostructuration in PP/elastomer blends, especially from the perspective of dielectrics, have yet to be systematically explored. In the current work, magnesia (MgO) nanofiller is added to a model PP/EPDM blend system to determine the effect of MgO on the breakdown properties of PP/EPDM. The results show that adding 0.5 wt% of MgO to PP/EPDM reduces the AC and DC breakdown strengths by 7% and 16%, respectively. As the amount of MgO increases to 3 wt%, the AC and DC breakdown strength reduces further by 25% and 29%, respectively. Significantly, appropriate modification of the nanocomposites with polypropylene-graft-maleic anhydride (PP-g-MAH) can result in 5% higher breakdown strength of the nanocomposites with respect to comparable nanocomposites without modification. The mechanisms surrounding these breakdown effects are discussed with the aid of materials structure interpretations. Overall, the results demonstrate that appropriate modification of nanocomposites with PP-g-MAH is crucial in tailoring breakdown properties of PP blend nanocomposites.

Finite Element Analysis of Anterior Implant-Supported Restorations with Different CAD-CAM Restorative Materials.

Due to the lack of literature concerning the selection of crown materials for the restoration of anterior teeth, this study aimed to investigate the effects of six distinct computer-aided design and computer-aided manufacturing (CAD-CAM) crown materials on stress and strain distribution within implant-supported maxillary central incisor restorations, employing finite element analysis (FEA). Furthermore, a comparative analysis was conducted between models that incorporated adjacent natural teeth and those that did not, intending to guide the selection of the most suitable modeling approach. Crown materials, including Lava Ultimate, Enamic, Emax CAD, Suprinity, Celtra Duo, and Cercon xt ML, were the subjects of the investigation. FEA models incorporating Coulomb friction were developed. These models were subjected to an oblique load, simulating the average maximum bite force experienced by anterior teeth. The potential for failure in titanium implant components and the prosthesis crown was evaluated through von Mises and principal stress, respectively. Furthermore, the failure of crestal bone was assessed through principal strain values. Stress values for each implant component and strain values of the bone were extracted from the models. To assess the impact of the six groups of crown materials, Kruskal-Wallis analysis of variance and post-hoc comparisons were conducted. Additionally, a statistical comparison between the two groups with Lava Ultimate and Cercon xt ML was performed using the Mann-Whitney U test to determine the difference in the two modeling approaches. Higher crown material stiffness led to decreased stress in the abutment, fixture, and retaining screw, along with reduced strain in the surrounding bone. However, the decrease in stress and strain values became less significant with increasing crown stiffness. Additionally, the model with adjacent teeth showed significantly lower stress and strain concentrations compared to the model without adjacent teeth. Crowns with a high elastic modulus were the optimal choice for anterior teeth restoration. Constructing FEA models with adjacent teeth was highly recommended to gain a deeper understanding of the mechanical behavior of dental implant restorations.

A phase-field model for the brittle fracture of Euler–Bernoulli beams coupling stretching and bending

Damage gradient models seek to simulate fracture mechanics by modulating the material stiffness. Within this framework, a singular scalar field representing damage is commonly utilized to globally decrease elastic energy. However, when considering structural models like beams and plates, this approach often fails to adequately capture important aspects due to the interaction between stretching and bending contributions. In this work, we propose a model for planar Euler–Bernoulli beams that incorporates the following features: firstly, we utilize two phase-field damage parameters to describe material damaging, specifically addressing the ‘erosion’ occurring above and below the original, undamaged beam; secondly, we assume a simple linear dependence of the axial stress field on the thickness coordinate, along with linear dependence on the axial force and bending moment. By appropriately identifying the constitutive response, our model effectively considers the coupling between stretching and bending induced during through-the-thickness damage, demonstrating good agreement with 2D observations.

Landing cushioning analysis of new generation heavy airborne armored vehicles

PurposeThe purpose of this study is to ensure the successful implementation of a landing cushion for the new generation armored vehicles with significantly enhanced quality. Furthermore, to introduce a high-precision landing cushioning analysis model.Design/methodology/approachTo accurately analyze the cushioning performance of the new generation armored vehicles, a nonlinear finite element dynamics model considering the complex travel system was established. The model considered the influence of various nonlinear factors to measure the dynamic response difference between the proposed and traditional models. The cushioning performance of airbags under different landing conditions and their various influence factors were analyzed.FindingsThe travel system has a large influence on the key points of the vehicle, whose rear end of the upper deck has a larger acceleration fluctuation compared with the traditional model. The increase in the body material stiffness is helpful to reduce this fluctuation. The established nonlinear finite element model can effectively analyze the landing cushioning performance of airborne armored vehicles. The area of the external airbag vent has a large influence on the cushioning performance, and the cushioning system has excellent cushioning performance under various operating conditions.Practical implicationsThis study introduces the travel system, which is ignored by traditional analytical models. The interactions between various types of complex structures are included in the analysis process in its entirety, leading to valuable new conclusions. Quantitatively reveals the analytical errors of traditional simulation models in multiple dimensions and the reasons for their formation. Based on a high-precision simulation model, it is verified that the designed airbag cushioning system has an excellent cushioning effect for the new generation of heavy airborne armored vehicles.Originality/valueThe novelty of this work comes from the need for smooth landing with low overload for a new type of large-load airborne armored vehicle and provides a high-precision model that quantifies the traditional analytical modeling errors and error principle.

First principle calculations to explore the electronic, mechanical and optical properties of 2D NiX2 (X = O, S, Se) monolayers

This investigation employs ab-initio calculations to investigate the structural, dynamical, mechanical, and optoelectronic attributes of 1T-NiX2 (X = O, S, Se) monolayers. The confirmation of structural and dynamical stability is derived from negative cohesive energy values and the absence of negative frequencies in phonon dispersion spectra. Mechanical stability is established through the application of the Born-Huang stability criterion. Results indicate that an increase in the X-atom size from O to Se induces a reduction in material stiffness from 137.64 Nm−1 to 77.56 Nm−1 and thus, enhances the flexibility of the monolayers. The NiX2 monolayers exhibit indirect bandgap features with values 1.33 eV (1.81 eV), 0.63 eV (0.61 eV) and 0.28 eV (0.28 eV) using PBE (PBE+U) methods. Present results show an inverse relations between the band gap and the size of the X atom. The scanning tunnelling microscope (STM) images of 2D NiX2 monolayers are also simulated for experimental observations. Additionally, exploration of optical characteristics reveals high optical absorption (105 cm−1), which lies from infrared to UV-region. Moreover, NiO2 can be utilized as good wave anti-reflectors with reflection of incident light less than 7%. These results suggest NiX2 materials as promising candidates for diverse applications in optoelectronic and photovoltaic devices.

Effect of temperature on the mechanical properties of aluminum polycrystal using molecular dynamics simulation

The initial temperature has a considerable effect on aluminum polycrystals' physical stability and mechanical performance, with the possibility to optimize their mechanical properties for practical applications. Thus, using a molecular dynamics technique, the effect of temperature on the mechanical properties of aluminum polycrystals is studied. Stress-strain curves, ultimate strength, and Young's modulus were all measured at temperatures of 300, 350, 400, and 450 K. The findings from MD simulations show that the initial temperature significantly affects the physical stability and mechanical performance of designed aluminum polycrystals. The aluminum polycrystal experiences a numerical increase in ultimate strength and Young's modulus from 6640 to 74.072 to 7.055 and 79.226 GPa, respectively, when subjected to the optimal initial conditions of 350 K. With further increasing temperature to 450 K, ultimate strength and Young's modulus decrease to 6.461 and 74.413 GPa, respectively. The observed decrease in ultimate strength and Young's modulus of the aluminum polycrystal as the temperature increased from the optimal condition of 350 K–450 K can be attributed to the weakening of interatomic attraction forces at higher temperatures. This reduction in interatomic bonding strength resulted in decreased material stiffness and resistance to deformation, leading to lower ultimate strength and Young's modulus values. This study's novelty lies in its comprehensive assessment of the initial temperature's effects on the mechanical performance of aluminum polycrystals, providing valuable insights for practical applications and advancing beyond previous efforts in the literature.

Heat-inducible CAR-T overcomes adverse mechanical tumor microenvironment in a 3D bioprinted glioblastoma model

Glioblastoma (GBM) presents a significant therapeutic challenge due to the limited efficacy of existing treatments. Chimeric antigen receptor (CAR) T-cell therapy offers promise, but its potential in solid tumors like GBM is undermined by the physical barrier posed by the extracellular matrix (ECM). To address the inadequacies of traditional 2D cell culture, animal models, and Matrigel-based 3D culture in mimicking the mechanical characteristics of tumor tissues, we employed biomaterials and digital light processing-based 3D bioprinting to fabricate biomimetic tumor models with finely tunable ECM stiffness independent of ECM composition. Our results demonstrated that increased material stiffness markedly impeded CAR-T cell penetration and tumor cell cytotoxicity in GBM models. The 3D bioprinted models enabled us to examine the influence of ECM stiffness on CAR-T cell therapy effectiveness, providing a clinically pertinent evaluation tool for CAR-T cell development in stiff solid tumors. Furthermore, we developed an innovative heat-inducible CAR-T cell therapy, effectively overcoming the challenges posed by the stiff tumor microenvironment.

Experimental evaluation of dynamic geotechnical parameters of tailings

The paper is focused on the testing of material from the "Lyulyakovitsa" tailings dam situated in proximity to the town of Panagyurishte in Bulgaria. The primary objective of this study is to investigate various laboratory techniques aimed at determining essential dynamic characteristics of the studied material. This research is conducted with the goal of subsequently assessing the seismic response of the existing tailings dam. In the context of performing an equivalent linear analysis, a widely used approach in geotechnical earthquake engineering, several crucial relationships and parameters come into play. These include the material's stiffness degradation, the damping ratio, and the small-strain stiffness, expressed through the shear wave velocity. The paper describes analysis of three experiments carried out in the geotechnical laboratory "Komaba" at the University of Tokyo. These experiments introduce undrained cyclic triaxial tests conducted under identical relative density (95%) of the tailings and executed at 50 kPa, 80 kPa, and 100 kPa effective confining stress, specifically, respectively. Additionally, two distinct testing methods were employed to measure the shear wave velocity in the specimens. The findings align with certain established directions in the existing literature for characterizing the dynamic properties of granular soils. Simultaneously, they underscore the practicality of the laboratory experiments adopted for acquiring a comprehensive set of relationships and parameters.

Ovariectomy-Induced Arterial Stiffening Differs From Vascular Aging and Is Reversed by GPER Activation.

Arterial stiffness is a cardiovascular risk factor and dramatically increases as women transition through menopause. The current study assessed whether a mouse model of menopause increases arterial stiffness in a similar manner to aging and whether activation of the G-protein-coupled estrogen receptor could reverse stiffness. Female C57Bl/6J mice were ovariectomized at 10 weeks of age or aged to 52 weeks, and some mice were treated with G-protein-coupled estrogen receptor agonists. Ovariectomy and aging increased pulse wave velocity to a similar extent independent of changes in blood pressure. Aging increased carotid wall thickness, while ovariectomy increased material stiffness without altering vascular geometry. RNA-sequencing analysis revealed that ovariectomy downregulated smooth muscle contractile genes. The enantiomerically pure G-protein-coupled estrogen receptor agonist, LNS8801, reversed stiffness in ovariectomy mice to a greater degree than the racemic agonist G-1. In summary, ovariectomy and aging induced arterial stiffening via potentially different mechanisms. Aging was associated with inward remodeling, while ovariectomy-induced material stiffness independent of geometry and a loss of the contractile phenotype. This study enhances our understanding of the impact of estrogen loss on vascular health in a murine model and warrants further studies to examine the ability of LNS8801 to improve vascular health in menopausal women.

Material Research for Hypersonic Travel

The goal of travelling faster than five times the speed ofsound, or hypersonic travel, has enormous potential to transform global transportation, defence capabilities, and space access. However, materials and structures face severe obstacles because to harsh aerothermal conditions inherent in high Mach number trajectories. This work focuses on new approaches to do research for ceramics, composites, and refractory alloys that are essential for building hypersonic vehicles. Essential design concepts for primary structures, heat shielding, and propulsion systems are covered, highlighting the critical role that theory and computation play in comprehending the links between structure, property, and processing. The remarkable high-temperature capabilities, stiffness, strength, and corrosion resistance of ceramic materials are highlighted in the study as reasons for theirincreasing importance in aircraft applications. Based on their distinct features, titanium alloys, nickel aluminides, metal- matrix composites, carbon-carbon, and ceramic-matrix composites stand out as top choices for a high temperature. In pursuit of lightweight, high- performance materials for hypersonic travel, this paper summarises ongoing researchefforts, evaluates the state of the art, offers insights into technological hurdles, and identifies areas that require future improvement. To explore the complex field of hypersonicmaterials design and selection in this research, this paper hope to shed light on the critical role that materials science plays in pushing the boundaries of aerospace technology by investigating the special difficulties presented by hypersonic flight as well as the characteristics and potential of various material classes.

In Vivo Corneal Biomechanical Response to Three Different Laser Corneal Refractive Surgeries.

To compare the effects of three common refractive surgeries on corneal biomechanics. Two hundred seven patients who had refractive surgery were included in this study, of whom 65 received transepithelial photorefractive keratectomy (tPRK), 73 received femtosecond laser-assisted laser in situ keratomileusis (FSLASIK), and 69 received small incision lenticule extraction (SMILE). Each patient had biomechanical measurements using the Corvis ST (Oculus Optikgeräte GmbH) preoperatively and at 3 and 6 months postoperatively. The measurements included five parameters expected to be associated with corneal biomechanics: deformation amplitude ratio at 2 mm (DAR2), integrated inverse radius (IIR), stiffness parameter at first applanation (SP-A1), highest concavity time (HCT), and the updated stress-strain index (SSIv2). The variations in these parameters postoperatively among the three surgeries, and their relationship with corneal thickness (CCT) and intraocular pressure measured by the Dynamic Contour Tonometer (DCT-IOP) were analyzed. SP-A1 decreased significantly from preoperatively to 3 months postoperatively in all three groups, whereas DAR2 and IIR increased significantly, all indicating stiffness losses. Between 3 and 6 months postoperatively, the results were inconsistent, with DAR2 decreasing (indicating stiffness increases) and IIR increasing (denoting stiffness decreases) in the FS-LASIK and SMILE groups. The decrease in SSIv2 (the only measure of corneal material stiffness) postoperatively was comparatively less pronounced at both 3 and 6 months postoperatively. On the other hand, HCT remained generally stable after all three surgeries. Unlike DAR2, IIR, and SP-A1, the changes postoperatively in stiffness parameters HCT and SSIv2 were independent of the corresponding changes in both DCT-IOP and CCT. Among the stiffness parameters considered, SSIv2 was not correlated with CCT or DCT-IOP, and holds promise for representing the corneal material stiffness and how it remains largely unaffected by refractive surgeries. Overall, FS-LASIK had the most significant impact on corneal stiffness, followed by SMILE, and finally tPRK. [J Refract Surg. 2024;40(5):e344-e352.].

Enteral Protease Inhibition Preserves Aortic Ultrastructure and Mechanics in Experimental Trauma/Hemorrhagic Shock

Introduction: Vascular compliance of large arteries is often overlooked in acute trauma/hemorrhagic shock (T/HS), as standard interventions, such as vasopressors, typically target systemic vascular resistance (SVR) regulated by small arterioles. However, patients may become refractory to vasopressors, and efforts to raise SVR may not restore mean arterial blood pressure (MAP), which is crucial for organ perfusion. We have previously reported compromised vascular compliance after T/HS in vivo with increased pulse wave velocity and ex vivo with diminished circumferential distensibility, that were both partially mitigated by enteral serine protease inhibition. To further elucidate the mechanisms behind these adverse changes, our aim was to directly assess the material stiffness, extracellular matrix (ECM) morphology, and matrix metalloproteinase (MMP) activity within the aortic wall tissue after T/HS, as well as to evaluate the effectiveness of enteral protease inhibition in this context.Methods: Anesthetized Wistar rats (350 - 400g) underwent laparotomy (trauma) and exsanguination to maintain a MAP of 35-40 mmHg for 90 minutes (shock). Animals were randomly assigned to receive either enteral gabexate mesilate protease inhibitor treatment (GM-treated) or vehicle-only (Untreated) via an orally-inserted catheter; investigators were blinded to the treatment assignation. At the conclusion of the shock period, animals were resuscitated with intravenous Lactated Ringer’s solution (LR) for two hours to achieve and maintain a MAP of at least 60 mmHg. A sham control group was also included for comparison. In all groups, the thoracic aorta was bisected, with one half sectioned for atomic force microscopy and histology and the other half homogenized for gelatin zymography. Liquid-phase force mapping was conducted on random areas (1600 μm2) of the medial layer in triplicate to determine the average Young’s modulus of the tissue. Collagen fibers were stained with picrosirius red, and elastin fibers were stained with Verhoeff Van Gieson. Results: After being subjected to T/HS and LR reperfusion, the aortic media of the Untreated group had a significantly higher average Young’s modulus than that of healthy sham vessels (862.7 kPa vs. 556.5 kPa, p < 0.05). The GM-treated group, however, better preserved its material elasticity (~650 kPa). These stiffness values negatively correlate with corresponding animals’ final MAP values measured at the end of the reperfusion period (r2 = 0.5031), supporting an association between vascular compliance and hemodynamic stability. The area of collagen within the tunica media was found to be significantly decreased in the Untreated compared to the sham group (4.93% vs. 10.26%, p < 0.05), but GM treatment was able to prevent collagen degradation (8.48%). Disruptions in elastin fibers were also observed at a higher frequency in the Untreated T/HS aorta compared to sham controls (3.3 vs. 1.7, p < 0.05) or GM-treated aortas (3.3 vs. 1.6, p < 0.05). Gelatin zymography revealed that enteral GM treatment also significantly attenuated elevated plasma MMP-9 (0.85 vs. 1.97 A.U., p < 0.01) and tissue MMP-2 activity (0.86 vs. 1.80 A.U., p < 0.05) seen following T/HS. Conclusions: Fluid-resuscitated traumatic hemorrhagic shock resulted in ultrastructural and biomechanical alterations in the aorta, indicating a loss in compliance. Enteral gabexate mesilate treatment effectively mitigated these pathological changes to the vasculature, suggesting the potential involvement of serine proteases in aortic ECM remodeling and large artery dysfunction in T/HS. Interventions against central artery impairment may be a promising strategy for improving blood pressure and survival in circulatory shock. Department of Defense Award W81XWH-17-2-0047. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Presence of XX Sex Chromosome Complement Increases Aortic Circumferential Stiffness in Female Mice

Elastin and collagen uniquely adapt to the mechanical demands of high pulsatile pressure in the vascular system in conjunction with the extracellular matrix (ECM). Elastic fiber networks and collagen are affected by component disorganization, leading to an array of vascular diseases and compromised mechanical behavior. It is shown that women than men have accelerated arterial stiffening. Previously, we have shown increased axial and circumferential linearized material stiffness in the carotid arteries of female than male wildtype mice. Whether sex hormones interact with sex chromosomes is unknown. Therefore, we hypothesize that sex hormones interact with sex chromosomes to increase aortic circumferential stiffening in female than male mice. In this study, we used gonadal intact 15-week-old four core genotype mice (n=4-6/group) comprising female (F) and male (M) mice with either XX or XY sex chromosome complement (SCC). Using a tissue puller, we assessed the stress-strain and displacement-force relationship of the abdominal aorta. Briefly, the aorta was cut into 3mm rings and pulled apart to a range of 1300 μm with a velocity of 35 μm/sec. To determine the load-bearing effect of collagen and elastin, collagenase type II (16 units) and elastase (5 units) were used to digest the aortic ring before pulling. Part of the aortic ring was digested for a PCR array of extracellular matrix and adhesion molecules. We observed a leftward shift of stress-strain in XXF than in XXM (P=0.03). A leftward shift of stress-strain was also indicated in XXF than in XYM mice (P=0.004). Displacement-force tests showed a similar effect with a leftward shift in XXF than XXM (P=0.01). A leftward shift of displacement force was also indicated in XXF than in XYM (P=0.004). Aorta digestion with elastase reversed the phenotype, showing a leftward shift of displacement force in XXM than in XXF (P=0.02). Collagenase digestion removed the observed sex differences in stress-strain and displacement force tests. The PCR array comparing XXF and XXM showed increased fold change in Adamts5 (4.2), Emilin (2.2), Icam1 (2.4), and Thbs2 (3). We also observed the downregulation of Cntn1 (0.4), Cntnna1 (0.5), Ecm1 (0.3), and Fbln1 (4). Our data suggested that XX sex chromosome complement, and ECM genes contribute to the structural stiffness of female mice aorta. Our study will contribute to understanding connective tissue diseases, including arterial stiffness, aortic aneurysms, Marfan and Danlos syndrome. HL105400 and HL155841. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Freeform Shape Fabrication by Kerfing Stiff Materials

AbstractFast, flexible, and cost efficient production of 3D models from 2D material sheets is a key component in digital fabrication and prototyping. In order to achieve high quality approximations of freeform shapes, a common set of methods aim to produce bendable 2D cutouts that are then assembled. So far bent surfaces are achieved automatically by computing developable patches of the input surface, e.g. in the context of papercraft. For stiff materials such as medium‐density fibreboard (MDF) or plywood, the 2D cutouts require the application of additional cutting patterns (“kerfing”) to make them bendable. Such kerf patterns are commonly constructed with considerable user input, e.g. in architectural design. We propose a fully automatic method that produces kerfed cutouts suitable for the assembly of freeform shapes from stiff material sheets. By exploring the degrees of freedom emerging from the choice of bending directions, the creation of box joints at the patch boundaries as well as the application of kerf cuts with adaptive density, our method is able to achieve a high quality approximation of the input.

Unsaturated polyester resin based composites: A case study of lignin valorisation

Materials from green resources boast a low carbon footprint, forming the foundation of the circular economy approach in materials science. Thus, in this study, waste poly(ethylene terephthalate) (PET) was subjected to depolymerization using propylene glycol (PG), and subsequent polycondensation with bio-based maleic anhydride (MA) produced unsaturated polyester resin (b-UPR). Bio-derived acryloyl-modified Kraft lignin (KfL-A) served as a vinyl reactive filler in the b-UPR matrix to create b-UPR/KfL-A composites. The structural characterization of KfL-A and b-UPR involved the use of FTIR and NMR techniques. The mechanical properties of the newly fabricated composites were assessed through tensile strength, Vickers microhardness, and dynamic mechanical tests. The addition of KfL-A to the rigid b-UPR matrix enhanced material flexibility, resulting in less stiff and hard materials while preserving composite toughness. For instance, incorporating 10 wt% of KfL-A in b-UPR led to a 17% reduction in hardness, a 48% decrease in tensile strength, and a 20% reduction in toughness. Positive environmental impact was achieved by incorporation of 64 wt% of renewable and recycled raw material. Analogously prepared b-UPR/KfL composites showed structural inhomogeneity and somewhat better mechanical properties. Transmission (TEM) and scanning (SEM) electron microscopies revealed a suitable relationship between mechanical and structural properties of composites in relation to the extent of KfL-A addition. The UL94V flammability rating confirmed that flame resistance increased proportionally with the KfL-A addition. Once deposited in a landfill, these composites are expected to disintegrate more easily than PET, causing less harm to the environment and contributing to sustainability in the plastics cycle.

Robust topology optimization for transient dynamic response minimization

This paper presents a novel framework for topology optimization (TO) of structures subjected to uncertain transient loading. Random transient uncertain but bounded loading is modeled in the form of an ellipsoid convex model. A transformation matrix is defined with uncertainty in input parameters based on orientation and lengths of semi-major and semi-minor axes of the ellipsoid. Latin hypercube sampling is utilized to generate samples inside the normalized space. These samples are then converted to a physical space using a transformation matrix. The generalized-α method is employed to compute the dynamic response of the system subjected to time-dependent loading. A density-based TO formulation is used to minimize dynamic response. The robust topology optimization problem is defined as bi-criteria optimization to minimize both the mean and variance across all deterministic cases within the ellipsoidal bounds. The solid isotropic material with penalization method is employed for the interpolation of material stiffness. Helmholtz filter is used to stabilize the problem numerically. The optimality criteria method is used to update the design variables. The proposed scheme’s effectiveness and the efficiency of the optimized designs are checked using a set of numerical examples. For most of the cases, robust design exhibits a substantial reduction of approximately 70%–75% in standard deviation when compared with deterministic design. The results demonstrate the proposed framework’s ability to reduce structure transient response under uncertain but bounded regions.

Optimized sulfur curing of pulse-damping rubber tubes

In pumping systems present in the industrial field, positive displacement pumps are used due to the high manometric loads and the characteristics of the extracted fluid. However, this type of pump provides a pulsating flow in the system that causes large pressure fluctuations, reducing the useful life of the installations. Because of this problem, pulsation dampers (attenuators) are used in the system in order to promote a more continuous flow and the good functioning of the process. In-line type attenuators feature a flexible tube composed of elastomer, whose viscoelastic behavior causes flow attenuation. The objective of this work is to evaluate whether there is a relationship between the sulfur content present in blends of natural rubber (NR) and synthetic rubber of the Butadiene Styrene (SBR) and the performance of tubular attenuators in a pumping system with pulsating flow. Four NR/SBR rubber blends with different sulfur concentrations in the formulation (0.5; 1.5, 3.0 and 4.5 phr) were tested. The rubbers were characterized using Fourier Transform Infrared Spectroscopy (FTIR) and their mechanical properties were analyzed using mechanical tensile tests. The efficiency of the attenuators was evaluated through bench tests that simulate pumping systems in the field. The results of the mechanical tests showed significant relationships with the performance of the attenuators in experimental tests. In attenuation tests, blends with 1.5; 3.0 and 4.5 phr sulfur had attenuation results of 27.06 %, 9.70 % and 1.61 %, respectively. The 0.5 phr attenuator could not withstand the applied loads due to lack of elastic properties. Thus, it was found that materials with a lower modulus of elasticity had greater efficiency in attenuating the pulsating flow and greater compliance, in which the attenuator that was formulated with 1.5 phr of sulfur showed 25.45 % greater pulsation damping than the stiffer material.

Fracture mechanics approach to TRISO fuel particle failure analysis

Weibull stress-based methods for failure probability assessment have been developed and analyzed to assess the integrity of tristructural isotropic (TRISO) fuel particles during fuel life cycles and accident operating conditions. While simple, these methods entail a number of drawbacks when stress concentrates near crack tips, including finite element mesh size dependency when the Weibull stress is averaged over the finite element domain. Fracture mechanics approaches involving the use of interaction integrals eliminate this lack of mesh convergence and produce consistent fracture predictions. In this work, we use an interaction integral approach to computing stress intensity factors for a crack in the inner pyrolytic carbon layer perpendicular to the silicon carbide layer, which is simplified representation of a failure mode in TRISO particles. The interface between these two TRISO layers has been shown to become porous, which we simulate by considering a transition of mechanical properties over such porous length, i.e. the layers are modeled as a functionally graded material. Aspects such as porosity and thermal and irradiation eigenstrains are considered in computing the stress intensity factor from a fracture mechanics approach and compared with the known Weibull stress failure approach. The methodology introduced in this paper enables a more general fracture probability assessment in TRISO particles and eliminates the need to identify best suited parameters when using local or averaged stress-based failure criterion. Finally, the numerical sensitivity studies show how parameters such as the porous transition zone length, the material stiffness, and creep affect the probability of TRISO fuel particle failure.