Mechanical Tolerance Research Articles

Impact response of 3D printed cornstalk-inspired structures: The effect of indenter shape on penetration

This paper reports the mechanical response and damage tolerance of 3D-printed cornstalk-inspired structures subjected to impact loading. Specimens were subjected to dynamic indentation tests at multiple impact energies with flat, hemispherical, and conical indenters. The mechanical properties of the base material (ABS) were measured across varying strain rates using a Shimadzu® Universal Testing Machine and a Split Hopkinson Pressure Bar. The effect of geometrical variations of the constituents on energy-absorbing capability was also investigated. Damage characteristics were interrogated through X-ray CT scans and provided detailed failure modes associated with each indenter shapes. Further, finite element simulations provided insights into the penetration mechanisms associated with the different indenter shapes. The results demonstrated that test specimens impacted by flat indenters absorbed ∼25 % less energy than those impacted by hemispherical and conical indenters. Among the various indenters, the conical shape had the highest duration of contact force within the specimen before experiencing failure by matrix cracking and complete perforation.

Central control of opioid-induced mechanical hypersensitivity and tolerance in mice.

Repetitive use of morphine (MF) and other opioids can trigger two major pain-related side effects: opioid-induced hypersensitivity (OIH) and analgesic tolerance, which can be subclassified as mechanical and thermal. The central mechanisms underlying mechanical OIH/tolerance remain unresolved. Here, we report that a brain-to-spinal opioid pathway, starting from μ-opioid receptor (MOR)-expressing neuron in the lateralparabrachial nucleus (lPBNMOR+) via dynorphin (Dyn) neuron in the paraventricular hypothalamic nucleus (PVHDyn+) to κ-opioid receptor (KOR)-expressing GABAergic neuron in the spinal dorsal horn (SDHKOR-GABA), controls repeated systemic administration of MF-induced mechanical OIH and tolerance in mice. The above effect is likely mediated by disruption of dorsal horn gate control for MF-resistant mechanical pain via silencing of the Dyn-positive GABAergic neurons in the SDH (lPBNMOR+ → PVHDyn+ → SDHKOR-GABA → SDHDyn-GABA). Repetitive binding of MF to MORs during repeated MF administration disrupted the above circuits. Targeting the above brain-to-spinal opioid pathways rescued repetitive MF-induced mechanical OIH and tolerance.

Effect of Deep Cryogenic Treatment on the Mechanical Properties and Defect Tolerance of Selective-Laser-Melted 316L Stainless Steel

Effect of Deep Cryogenic Treatment on the Mechanical Properties and Defect Tolerance of Selective-Laser-Melted 316L Stainless Steel

Fabrication of liquid-free ionic conductive elastomer (ICE) from cellulose-rosin derived poly(esterimide) towards temperature-tolerant and solvent-resistant UV shadowless adhesive and sensor

Recently, the utilization of the cellulose to fabricate the multifunctional materials with aim to replace the petroleum-based product, is receiving significant attentions. However, the development of cellulose-based multifunctional materials with high mechanical strength and temperature resistance is still a challenge. Herein, the intrinsic feature and property of cellulose and rosin were creatively employed to fabricate a novel cellulose-rosin based poly(esterimide) (PEI) by esterification reaction and imidization reaction, and the obtained cellulose-rosin derived PEI exhibits superior thermal stability. Then the as-prepared cellulose-rosin derived PEI was dissolved in polymerizable deep eutectic solvents (PDES) and in-situ formed the ionic conductive elastomer (ICE) with via UV-induced polymerization. These cellulose-rosin based ICE exhibited excellent mechanical properties, solvent resistance, and temperature tolerance. By adjusting the mass ratio of cellulose-rosin derived PEI and PDES, the as-prepared liquid-free ICE functions as UV shadowless adhesive and wearable sensors. The bonding strength of UV shadowless adhesive could 1.52 MPa, which could be applied to fix the broken glass toy models. Furthermore, wearable sensors based those ICE could monitor the large and subtle movements even under extreme environmental condition, such as being soaked in organic solvent (such as tetrahydrofuran) or at low/high temperature (−25 °C or 80 °C). This work opens a new avenue for the next-generation of multifunctional ICE.

Achieving Remarkable Specific Mechanical Strength and Energy Absorption Capacity in SiC Nanowire Networks through Graded Structural Design.

Lightweight porous ceramics with a unique combination of superior mechanical strength and damage tolerance are in significant demand in many fields such as energy absorption, aerospace vehicles, and chemical engineering; however, it is difficult to meet these mechanical requirements with conventional porous ceramics. Here, we report a graded structure design strategy to fabricate porous ceramic nanowire networks that simultaneously possess excellent mechanical strength and energy absorption capacity. Our optimized graded nanowire networks show a compressive strength of up to 35.6 MPa at a low density of 540 mg·cm-3, giving rise to a high specific compressive strength of 65.7 kN·m·kg-1 and a high energy absorption capacity of 17.1 kJ·kg-1, owing to a homogeneous distribution of stress upon loading. These values are top performance compared to other porous ceramics, giving our materials significant potential in various engineering fields.

Compressive Failure Characteristics of 3D Four-Directional Braided Composites with Prefabricated Holes.

The low delamination tendency and high damage tolerance of three-dimensional (3D) braided composites highlight their significant potential in handling defects. To enhance the engineering potential of three-dimensional four-directional (3D4d) braided composites and assess the failure mode of hole defects, this study introduces a series of 3D4d braided composites with prefabricated holes, studying their compressive properties and failure mechanisms through experimental and finite element methods. Digital image correlation (DIC) was used to monitor the compressive strain on the surface of materials. Scanning acoustic microscope (SAM) and scanning electron microscopy (SEM) were used to characterize the longitudinal compression failure mode inside the material. A macroscopic model is established, and the porous materials are predicted by using the general braided composite material prediction theory. While reducing the forecast cost, the error is also controlled within 21%. The analysis of failure mechanisms elucidates the damage extension mode, and the porous damage tolerance ability aligns closely with the bearing mode of braided material structure. Different braiding angles will lead to different bearing modes of materials. Under longitudinal compression, the average strength loss of 15° specimens is 38.21%, and that of 30° specimens is 8.1%. The larger the braided angle, the stronger the porous damage tolerance. Different types of prefabricated holes will also affect their mechanical properties and damage tolerance.

Reflectivity measurement of a silicon carbide mirror sample for ITER divertor vacuum ultraviolet spectrometer.

The first mirror is the front-end optic component that reflects light emitted from the plasma to the diagnostic system in fusion plasmas. Silicon carbide (SiC), known for its relatively high mechanical strength and radiation tolerance, has been selected as the substrate material for the first mirror in the ITER divertor vacuum ultraviolet (VUV) spectrometer. To measure the reflectivity of the ellipse cylindrical SiC mirror to be manufactured, a device for reflectivity measurement in the VUV wavelength range was developed. First, the reflectivity of a sample SiC mirror (15mm diameter × 10mm thick) was measured across the ITER-required incidence angles, and the results are reported in this study. A hollow cathode lamp with helium gas was used as the VUV light source in the wavelength range of 23-60nm, and a dedicated VUV spectrometer to select specific wavelengths was developed. The spectrometer utilized laminar-type replica diffraction gratings (Shimadzu 30-006) and two back-illuminated charge-coupled devices (BI-CCD, Andor DO 940P-BEN) for the grating and detector, respectively. A cropping technique with aperture was employed to precisely localize the VUV light's reflection onto the SiC mirror surface. The experimentally measured reflectivity values of SiC at the required incidence angles of VUV light were compared with theoretically calculated reflectivity curves. The oxidation layer (SiO2) formed on the SiC surface and the incidence angle of VUV light to the BI-CCD chip (E2V) would be the factors affecting the accuracy of the reflectivity.

Finite element modeling and injury criteria investigation for the lower leg of the Chinese human body under impact loads

The widely used human body injury criteria were established based on the biomechanical response of the Euro-American human body, without considering the difference in the body anthropometry and injury characteristics among different races, particularly the Chinese human body that has the smaller body size. The absence of such race specific design considerations negatively influences the injury prevention capability for these populations, and weakens the applicability of injury criteria. To resolve these issues, this study aim to develop a lower leg finite element model of a 50th percentile Chinese male. The model is built based on the medical images of an average size Chinese male with detailed ankle ligaments and lower leg muscles modeled. Sixty experiments available in the literature are used to validate its biofidelity. Using the validated model, the lower leg model is subjected to combined axial compression and bending loads to evaluate its injury criteria. Compared with a typical Euro-American human body mode, the Chinese lower leg presents lowered mechanical tolerance, and the revised tibia index may be an option to be the injury criteria for the Chinese lower leg. Additionally, the validated model reproduces the pedestrian lower leg fracture in a domestic accident.

Enhancing mechanical properties and damage tolerance of additive manufactured ceramic TPMS lattices by hybrid design

AbstractMany studies have reported that additive manufactured ceramic lattices with microarchitectures often exhibit low‐strain brittle fracture behavior. In this work, the fracture behavior of ceramic triply periodic minimal surface (TPMS) lattices was optimized by introducing a hybrid design strategy that utilizes different microarchitectures. Hybrid ceramic TPMS structures incorporating Gyroid and Primitive unit cells were successfully fabricated using the Lithography‐based ceramics manufacturing (LCM) technique, and their mechanical properties were evaluated under both quasistatic and dynamic compression. The hybrid designs exhibited improved damage tolerance and fracture strength compared to their normal counterparts. Compared to normal Gyroid and Primitive structures, the G2P2 structure exhibits the best energy absorption capacity of 12.5 × 104 J/m3, demonstrating a 13% and 217% increase in energy absorption capacity under quasistatic loading, respectively. Additionally, compared with other normal and hybrid designs, the G2P2 structure exhibits the highest fracture strength of 13.03 MPa under quasistatic loading conditions. Moreover, the P2G hybrid structure displayed a distinct deformation pattern characterized by a smoother stress decrease under quasistatic loading, enhancing damage tolerance. The order of Young's modulus under quasistatic loading was Normal Gyroid ≈ G2P2 > G2P1 > Normal Primitive > P2G. Fracture strength follows the order of G2P2 ≈ Normal Gyroid > Normal Primitive > G2P1 > P2G. The mechanical properties of hybrid TPMS structures suggest that the hybrid design strategy can broaden the achievable range of mechanical properties among ceramic TPMS structures.

Photoswitchable eutectogels with ultra-strength, high stretchability and adhesion for information encryption and multifunctional flexible sensor of signal transmission and human–computer interaction

Eutectogels are emerging as attractive soft conductors for flexible wearable electronics and next-generation human–computer interaction devices owing to their inherent environmental stability and high ionic conductivity. However, it remains a challenge to achieve efficient multifunctional integration of flexible wearable sensors through a convenient and environment-friendly approach. Herein, the eutectogel with excellent mechanical properties, self-healing, environmental tolerance, reversibly fluorescent and high conductivity was prepared via a facile UV-initiated one-step polymerization. Abundant hydrogen bonds and multiple dynamic interactions impart the eutectogel with excellent tensile strength (1.99 MPa), high stretchability (>1500 %), high toughness (20.85 MJ/m3), strong self-adhesion (192 kPa), and autonomously self-healing (>92 %) capabilities. Due to the dynamic photochemical reaction of the anthracene groups, the eutectogel exhibits tunable and reversible fluorescence. The eutectogel-based flexible wearable devices and wireless interaction systems can be used for non-contact information writing and transmission, motion monitoring, wireless communication, and human–computer interaction, which achieves the working modes of digital and visual signals complementing each other as well as efficient multifunctional integration. Therefore, this simple and environment-friendly design concept can provide new ideas for the development of multifunctional integrated portable flexible sensing devices and wireless interactive systems.

Construction of flexible carbon nanotube film/PA66 composite with high dynamic mechanical properties

Carbon nanotube (CNT) has potential application in many fields owing to its excellent properties, but the weak Van der Waals forces between randomly arranged tube bundles limit their mechanical properties. In this paper, CNT films were prepared by floating catalyst chemical vapor deposition (FCCVD), whereas PA66 resin was introduced via impregnation and hot press curing in order to further improve the mechanical tensile properties and environmental resistance of the films. The results demonstrate that the tensile properties of PA66-impregnated CNT film are significantly improved. When the mass fraction of PA66 is 1 %, the composite film exhibits the best tensile properties under quasi-static conditions, with a tensile strength of 528 MPa and an energy absorption (EA) value of 109.5 MJ/m3. Plus, at the high strain rate of 2900 s−1, the strength and EA of CNT film/PA66 composite can reach 534 MPa and 107 MJ/m3, respectively. The results in present research can provide a feasible and effective strategy for the design of CNT composite film with high mechanical tolerance which will broaden the application field to a large extent.

Advanced-design cross-linked binder enables high-performance silicon-based anodes through in-situ crosslinking based on sodium carboxymethyl cellulose and poly-lysine

Practical employment of silicon (Si) electrodes in lithium-ion batteries (LIBs) is limited due to the severe volume changes suffered during charging-discharging process, causing serious capacity fading. Here, a composite polymer (CP-10) containing sodium carboxymethyl cellulose (CMC-Na) and poly-lysine (PL) is proposed for the binder of Si-based anodes, and a multifunctional strategy of “in-situ crosslinking” is achieved to alleviate the severe capacity degradation effectively. A cross-linked three-dimensional (3D) network is established through the strong hydrogen bonding interaction and reversible electrostatic interactions within CP-10, offering favorable mechanical tolerance for the extreme volume expansion of Si. Moreover, hydrogen bonding interaction along with ion-dipole interaction formed between CP-10 and Si surface enhance the bonding capability of Si-based anodes, promoting the maintenance of anodes' integrity. Consequently, over 800 cycles are achieved for the Si@CP-10 at 0.5C while maintaining a fixed discharge specific capacity of 1000 mAh g−1. Moreover, the Si/C@CP-10 can stably operate over 500 cycles with a capacity retention of 77.12 % at 1C. The prolonged cycling lifetime of Si/C and Si anodes suggests great potential for this strategy in promoting the implementation of high-capacity LIBs.

Freeze-Thaw Cycle Durability and Mechanism Analysis of Zeolite Powder-Modified Recycled Concrete.

The inferior mechanical performance and freeze-thaw (FT) resistance of recycled concrete are mostly due to the significant water absorption and porosity of recycled coarse particles. In this study, different dosages of zeolite powder were used in recycled concrete. A series of macroscopic tests were used to evaluate the workability and FT durability of zeolite powder-modified recycled concrete (ZPRC). X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to reveal the micro-mechanisms of FT resistance in ZPRC. The results show that the increase in zeolite powder content leads to a decrease in the slump and water absorption of ZPRC. Additionally, ZPRC with 10% zeolite powder has superior mechanical characteristics and tolerance to FT conditions. The higher strength and FT resistance of the ZPRC can be attributed to the particle-filling effect, water storage function, and pozzolanic reaction of zeolite powder, which results in a denser microstructure. The particle-filling effect of zeolite powder promotes the reduction of surface pores in recycled coarse aggregates (RCAs). The water storage function of zeolite powder can provide water for the secondary hydration of cement particles while reducing the free water content in ZPRC. The pozzolanic reaction of zeolite powder can also promote the generation of hydrated calcium silicate and anorthite, thereby making the microstructure of ZPRC more compact. These results provide theoretical guidance for the engineering application of recycled concrete in cold regions.

Bioinspired composite fiber aerogel pressure sensor for machine-learning-assisted human activity and gesture recognition

Machine-learning-assisted human activity and gesture recognition are valuable for human-computer interaction, and data acquisition often necessitates high-performance sensors. Here, inspired by spider web and bat wing airflow sensing system, polyimide fiber (PIF)/carbon black (CB) composite fiber aerogel (CFA) pressure sensor with biomimetic hair-Merkel cell sensitive unit was developed, exhibiting ultralow detection limit (2 Pa), high pressure sensitivity (S=23.1 kPa-1), wide linear detection capacity up to 67.61 kPa, and fast response/recovery time (140/100 ms). Thanks to the excellent mechanical property and environmental tolerance of CFA, it also possesses excellent low fatigue over >4000 cycles and good durability even at extreme high-temperature (200 °C) and underwater conditions. The superior signal data of the sensor, combined with the Convolutional Neural Network machine learning algorithm, achieves ultra-high prediction accuracies of 96.73% and 98.26% for human activity and gesture recognition, respectively. Additionally, CFA also has amazing thermal management properties, making it to be an ideal candidate for wearable electronics with excellent wearing comfort and safety.

Long-Range Influence of Cr on the Stacking Fault Energy of Cr-Containing Concentrated Solid-Solution Alloys

Single-phase concentrated solid-solution alloys (CSAs) have exhibited excellent mechanical and radiation tolerance properties, making them potential candidate materials for nuclear applications. These excellent properties are closely related to dislocation movements, which depend on the stacking fault energies (SFEs). In CSAs, SFEs show large fluctuations due to variations in the local atomic environments in the vicinity of the stacking faults. In this work, first-principle calculations were performed to investigate the origin of the fluctuations in the SFEs of the widely studied CSA, NiCoCr, which show a very wide distribution from about −200 mJ/m2 to 60 mJ/m2. Compared to the common understanding that only atoms in close proximity to the stacking fault influence the SFEs in pure metals and dilute alloys, charge redistribution can be observed in several nearby planes of the stacking fault in NiCoCr, indicating that atoms several atomic layers away from stacking fault also contribute to the SFEs. Our analysis shows that Cr plays a major role in the large fluctuation in the SFEs of NiCoCr based on both electronic and magnetic responses. The flexible electronic structure of Cr facilitates easier charge transfer with Cr in several nearby atomic planes near the stacking fault, leading to significant changes in the d-electron number, orbital occupation number, and magnetic moments of Cr.

Fully bio‐based flax/furan versus carbon/glass epoxy composites: Scope and limitations in terms of fire and physico‐mechanical performances

AbstractFire and mechanical performances of a bio‐based flax/furan resin composite are evaluated and, in order to assess their commercial potential, compared with those of conventional carbon/glass fiber‐reinforced composites. Fire retardant (FR) variants of flax/furan were obtained by adding FRs to the resin and using (i) flax or (ii) FR‐treated flax fabrics. With (i), the fire hazard of the composite could be reduced to minimum, without detrimental effect on the mechanical properties. However, use of FR‐flax fabric (ii) led to impairment of mechanical properties. This indicated that for optimized fire and mechanical properties, use of a FR in the resin matrix suffices; there is no advantage in using a FR‐treated flax fabric. Natural aging of the samples for 10 years followed by water aging indicated that water absorption in flax/furan composites was much higher than in comparable carbon/epoxy composites. While there was evidence of released acidic components such as acetic acid, oxalic acid, and so forth, in flax/furan composites, mainly from oxidative degradation of furan resin, there was no evidence of leaching of FR additives from the matrix. However, FR treatment of flax fabric affected the fiber–matrix interfacial adhesion, leading to considerable water absorption during aging and disintegration of the reinforcement.Highlights Furan resins are naturally fire retardant, burn only under forced combustion. FR flax/furan composites obtained by adding FRs to the resin or the flax fabric. FR treatment of the flax impairs mechanical properties and water tolerance. FRs in the resin neither affect mechanical properties nor leach out in water.

Tunable H-bond effects enabled ionic conductive gels with high stretchability, transparency, self-adhesion and wide environmental tolerance for e-skin

It is a high demand but a great challenge to construct all-in-one ionic conductive hydrogels with excellent mechanical performances, transparency, self-adhesion, conductivity and environmental tolerance. Herein, a versatile gel platform was developed via a facile and rapid photopolymerization of acrylic acid (AA) in deep eutectic solvent (DES) with multiple roles simultaneously as water-free solvent, ionic conductor, regulator of hydrogen bond density. Benefiting from the formed crosslinking networks including covalently cross-linked polymer network and multiple dynamic interactions, the resultant PAA-DES gels exhibited high stretchability of 884.7 ± 4.9%, toughness of 31.2 ± 1.4 MJ/m3, fatigue resistance and recovery ability, transparency of 93%, self-adhesive strength of 472 kPa. Moreover, the inherent advantages of DES enabled the gels with good ionic conductivity (2.5 ± 0.2 mS/cm), wide working window and biocompatibility. The PAA-DES as self-adhesive ionic sensors not only possessed wide strain range (∼400%) and stability, but also displayed excellent humidity (30–80%), temperature (−40–60 °C), and sweat tolerance which could precisely and steadily discern and monitor human motions and weak physiological signals. Thus, this work not only provides a strategy to construct all-in-one ionic conductive gels with high elasticity, fatigue resilience, transparency, self-adhesion and wide environmental tolerance, but also exploits versatile platform for intelligent gel sensor and e-skin.

Stabilizing High-Nickel Cathodes via Interfacial Hydrogen Bonding Effects Using a Hydrofluoric Acid-Scavenging Separator

Nickel-rich layered Li transition metal oxides are the most promising cathode materials for high-energy-density Li-ion batteries. However, they exhibit rapid capacity degradation induced by transition metal dissolution and structural reconstruction, which are associated with hydrofluoric acid (HF) generation from lithium hexafluorophosphate decomposition. The potential for thermal runaway during the working process poses another challenge. Separators are promising components to alleviate the aforementioned obstacles. Herein, an ultrathin double-layered separator with a 10 μm polyimide (PI) basement and a 2 μm polyvinylidene difluoride (PVDF) coating layer is designed and fabricated by combining a non-solvent induced phase inversion process and coating method. The PI skeleton provides good stability against potential thermal shrinkage, and the strong PI–PVDF bonding endows the composite separator with robust structural integrity; these characteristics jointly contribute to the extraordinary mechanical tolerance of the separator at elevated temperatures. Additionally, unique HF-scavenging effects are achieved with the formation of –CO···H–F hydrogen bonds for the abundant HF coordination sites provided by the imide ring; hence, the layered Ni-rich cathodes are protected from HF attack, which ultimately reduces transition metal dissolution and facilitates long-term cyclability of the Ni-rich cathodes. Li||NCM811 batteries (where “NCM” indicates LiNixCoyMn1−x−yO2) with the proposed composite separator exhibit a 90.6% capacity retention after 400 cycles at room temperature and remain sustainable at 60 °C with a 91.4% capacity retention after 200 cycles. By adopting a new perspective on separators, this study presents a feasible and promising strategy for suppressing capacity degradation and enabling the safe operation of Ni-rich cathode materials.

Modular Protein Fibers with Outstanding High-Strength and Acid-Resistance Performance Mediated by Copper Ion Binding and Imine Networking.

Engineered protein fibers are promising biomaterials with diverse applications due to their tunable protein structure and outstanding mechanical properties. However, it remains challenging at the molecular level to achieve satisfied mechanical properties and environmental tolerance simultaneously, especially under extreme acid conditions. Herein, the construction of artificial fibers comprising chimeric proteins made of rigid amyloid peptide and flexible cationic elastin-like protein (ELP) module is reported. The amyloid peptide readily assembles into highly organized β-sheet structures that can be further strengthened by the coordination of Cu2+, while the flexible ELP module allows the formation of imine-based crosslinking networks. These double networks synergistically enhance the mechanical properties of the fibers, leading to a high tensile strength and toughness, overwhelming many reported recombinant spidroin fibers. Notably, the coordination of Cu2+ with serine residues could stabilize β-sheet structures in the fibers under acidic conditions, which makes the fibers robust against acid, thus enabling their successful utilization in gastric perforation suturing. This work highlights the customization of double networks at the molecular level to create tailored high-performance protein fibers for various application scenarios.

Comprehensive computational prediction of elasto-mechanical and thermoelectric properties of Co2PdAl and Co2AgAl full Heusler compounds

Without a profound knowledge of technological growth and future perspectives of materials their physical properties cannot be explained. Heusler compounds belong to class of prominent materials with special characteristics which ultimately land them as multifunctional materials. The results of this work stem the investigations of structural phase stability, elasto-mechanical and thermoelectric properties of Co2AgAl and Co2PdAl full Heuslers with the density functional theory (DFT). This theory is successfully executed in Boltzmann transport theory and WIEN2k program package to obtain the desired results. The generalised-gradient approximation (GGA) scheme and Tran Blaha modified Becke-Johnson (TB-mBJ) potential are embraced to compute the ground state properties. The approximations approves both compounds ideal for thermoelectric as well as for elasto-mechanical applications. The computation for mechanical parameters such as Young’s modulus, Shear modulus, Pugh’s ratio elastic constants and Poisson’s ratio are investigated. The mechanical tolerance ultimately revealed that both compounds Co2AgAl and Co2PdAl are stable with ductile nature and exhibit low rigidity. The thermodynamic parameters like Seebeck coefficient, thermal conductivity electrical conductivity, lattice thermal and electronic conductivity, power factor (ɳ) and electrical figure of merit (zT) have been computed within relaxation time approximation as a function of high temperature.