Revealing Na+-coordination induced Failure Mechanism of Metal Sulfide Anode for Sodium Ion Batteries.

Metal sulfide (MS) is regarded as a promising candidate of the anode materials for sodium-ion battery (SIB) with ideal capacity and low cost, yet still suffers from the inferior cycling stability and voltage degradation. Herein, the coordination relationship between the discharge product Na2S with the Na+ (NaPF6) in the electrolyte, is revealed as the root cause for the cycling failure of MS. Na+-coordination effect assistants the dissolution of Na2S, further delocalizing Na2S from the reaction interface under the function of electric field, which leads to the solo oxidation of the discharge product element metal without the participation of Na2S. Besides, the higher highest occupied molecular orbital of Na2S suggest the facilitated Na2S solo oxidation to produce sodium polysulfides (NaPSs). Based on these, lowering the Na+ concentration of the electrolyte is proposed as a potential improvement strategy to change the coordination environment of Na2S, suppressing the side reactions of the solo-oxidation of element metal and Na2S. Consequently, the enhanced conversion reaction reversibility and prolonged cycle life are achieved. This work renders in-depth perception of failure mechanism and inspiration for realizing advanced conversion-type anode.

Lithium Hydride in the Solid Electrolyte Interphase of Lithium-Ion Batteries as a Pulverization Accelerator of Silicon.

As a highly promising next-generation high-specific capacity anode, the industrial-scale utilization of micron silicon has been hindered by the issue of pulverization during cycling. Although numerous studies have demonstrated the effectiveness of regulating the inorganic components of the solid electrolyte interphase (SEI) in improving pulverization, the evolution of most key inorganic components in the SEI and their correlation with silicon failure mechanisms remain ambiguous. This study provides a clear and direct correlation between the lithium hydride (LiH) in the SEI and the degree of micron silicon pulverization in the battery system. The reverse lithiation behavior of LiH on micron silicon during de-lithiation exacerbates the localized stress in silicon particles and contributes to particle pulverization. This work successfully proposes a novel approach to decouple the SEI from electrochemical performance, which can be significant to decipher the evolution of critical SEI components at varied battery anode interfaces and analyze their corresponding failure mechanisms.

Preface to the theme issue 'physics-informed machine learning and its structural integrity applications'.

The issue focuses on physics-informed machine learning and its applications for structural integrity and safety assessment of engineering systems/facilities. Data science and data mining are fields in fast development with a high potential in several engineering research communities; in particular, advances in machine learning (ML) are undoubtedly enabling significant breakthroughs. However, purely ML models do not necessarily carry physical meaning, nor do they generalize well to scenarios on which they have not been trained on. This is an emerging field of research that potentially will raise a huge impact in the future for designing new materials and structures, and then for their proper final assessment. This issue aims to update the current research state of the art, incorporating physics into ML models, and providing tools when dealing with material science, fatigue and fracture, including new and sophisticated algorithms based on ML techniques to treat data in real-time with high accuracy and productivity. This article is part of the theme issue 'Physics-informed machine learning and its structural integrity applications (Part 1)'.

Physics-informed machine learning and its structural integrity applications: state of the art.

The development of machine learning (ML) provides a promising solution to guarantee the structural integrity of critical components during service period. However, considering the lack of respect for the underlying physical laws, the data hungry nature and poor extrapolation performance, the further application of pure data-driven methods in structural integrity is challenged. An emerging ML paradigm, physics-informed machine learning (PIML), attempts to overcome these limitations by embedding physical information into ML models. This paper discusses different ways of embedding physical information into ML and reviews the developments of PIML in structural integrity including failure mechanism modelling and prognostic and health management (PHM). The exploration of the application of PIML to structural integrity demonstrates the potential of PIML for improving consistency with prior knowledge, extrapolation performance, prediction accuracy, interpretability and computational efficiency and reducing dependence on training data. The analysis and findings of this work outline the limitations at this stage and provide some potential research direction of PIML to develop advanced PIML for ensuring structural integrity of engineering systems/facilities. This article is part of the theme issue 'Physics-informed machine learning and its structural integrity applications (Part 1)'.

Quantifying the Evolution of Inactive Li/Lithium Hydride and Their Correlations in Rechargeable Anode-free Li Batteries.

Electrolyte optimization, such as using fluoride-bearing electrolytes, is regarded as an effective way to improve the cycle performance of lithium metal batteries (LMBs), but the promotion mechanisms of the electrolytes are in controversy due to the lack of quantitative understanding of the reaction products during cycling. Here, taking several fluorinated electrolytes as models, we use mass spectrometry titration (MST) and solid state nuclear magnetic resonance (NMR) techniques to quantify the evolution of dead Li metal, solid electrolyte interphases (SEI) and lithium hydride (LiH) during cycling. Our quantitative results clearly disclose that lithium difluoro(oxalato)borate (LiODFB) is able to inhibit the formation of SEI and LiH while fluoroethylene carbonate (FEC) mainly inhibits the formation of dead Li metal. Furthermore, we surprisingly observe a linear correlation between LiH and SEI formation, whereas the commonly mentioned lithium fluoride (LiF) shows a weak correlation with either dead Li metal or SEI. Guided by the clear failure mechanism, we can provide a reasonable explanation for the synergistic effect with the combination of LiODFB and FEC from a quantitative perspective. We believe that a quantitative insight of electrolytes on the failure mechanism of LMBs will guide us to explore the functional electrolytes to achieve the practical application of LMBs.

In Situ TEM Technique Revealing the Deactivation Mechanism of Bimetallic Pd-Ag Nanoparticles in Hydrogen Sensors.

Bimetallic Pd-Ag alloy nanoparticles exhibit satisfactory H2-sensing improvements and show application potential for H2 sensor construction. However, the long-term stability of the H2 sensor with Pd-Ag nanoparticles as the catalyst is found to dramatically decrease during operation. Herein, gas-cell in situ transmission electron microscopy (TEM) is used to investigate the failure mechanisms of Pd-Ag nanoparticles under operation conditions. Based on the in situ TEM results, the Pd-Ag nanoparticles have two failure mechanisms: particles coalescence at 300 °C and phase segregation at 500 °C. Guided by the failure mechanisms, the H2 sensor is comprehensively optimized based on the working temperature and the amount of Pd-Ag alloy nanoparticles. The optimized sensor exhibits satisfactory H2-sensing properties, and the response decline of the sensor after 1 month is negligible. The revealing of the failure mechanisms with in situ TEM technology provides a valuable route for developing gas sensors with high long-term stability.

Revealing Capacity Degradation of Ge Anodes in Lithium-Ion Batteries Triggered by Interfacial LiH.

The Germanium (Ge), as a fast-charging and high specific capacity (1568 mAh g-1 ) alloy anode, is greatly hampered in practical application by poor cyclability. To date, the understanding of cycling performance degradation remains elusive. This study illustrates that, contrary to conventional beliefs, most of the Ge material in failed anodes still retains good integrity and does not undergo severe pulverization. It is revealed that capacity degradation is clearly correlated to the interfacial evolution of lithium hydride (LiH). Tetralithium germanium hydride (Li4 Ge2 H), as a new species derived from LiH, is identified as the culprit of Ge anode degradation, which is the dominant crystalized component in an ever-growing and ever-insulating interphase. The significantly increased thickness of the solid electrolyte interface (SEI) is accompanied by the accumulation of insulating Li4 Ge2 H upon cycling, which severely retards the charge transport process and ultimately triggers the anode failure. We believe that the comprehensive understanding of the failure mechanism presented in this study is of great significance to promoting the design and development of alloy anode for the next generation of lithium-ion batteries.

Failure mechanism of graphene kirigami under nanoindentation.

Though graphene is the strongest material in nature, its intrinsic brittleness hinders its applications where flexibility is the key figure of merits. In this work, we report the enhanced flexibility of graphene under nanoindentation by using kirigami technique. Based on molecular dynamics simulations, we find that graphene kirigami designed at the optimal cut parameter can sustain more than 45% larger out-of-plane deformation than its pristine counterpart while the maximum impact load is reduced by 20% due to the flexible cut edges. This trade-off between flexibility and strength in a graphene kirigami can be overcome by adding a pristine graphene as a supporting substrate. This double-layer structure consisting of one graphene kirigami and one pristine graphene can stand the maximum impact load three times larger than the single-layer graphene kirigami but its maximum indentation depth is merely 8% smaller. Our simulation results provide useful insights into the failure mechanism of the graphene kirigami under nanoindentation and useful guidelines to enhancing the flexibility of graphene for its applications as protection materials.

Vibration Analysis for Fault Detection of Wind Turbine Drivetrains-A Comprehensive Investigation.

Vibration analysis is an effective tool for the condition monitoring and fault diagnosis of wind turbine drivetrains. It enables the defect location of mechanical subassemblies and health indicator construction for remaining useful life prediction, which is beneficial to reducing the operation and maintenance costs of wind farms. This paper analyzes the structure features of different drivetrains of mainstream wind turbines and introduces a vibration data acquisition system. Almost all the research on the vibration-based diagnosis algorithm for wind turbines in the past decade is reviewed, with its effects being discussed. Several challenging tasks and their solutions in the vibration-based fault detection of wind turbine drivetrains are proposed from the perspective of practicality for wind turbines, including the fault detection of planetary subassemblies in multistage wind turbine gearboxes, fault feature extraction under nonstationary conditions, fault information enhancement techniques and health indicator construction. Numerous naturally damaged cases representing the real operational features of industrial wind turbines are given, with a discussion of the failure mechanism of defective parts in wind turbine drivetrains as well.

The Formation/Decomposition Equilibrium of LiH and its Contribution on Anode Failure in Practical Lithium Metal Batteries.

Discovering the underlying reason for Li anode failure is a critical step towards applications of lithium metal batteries (LMBs). In this work, we conduct deuterium-oxide (D2 O) titration experiments in a novel on-line gas analysis mass spectrometry (MS) system, to determine the content of metallic Li and lithium hydride (LiH) in cycled Li anodes disassembled from practical LiCoO2 /Li LMBs. The practical cell is comprised of ultrathin Li anode (50 µm), high loading LiCoO2 (17 mg cm-2 , 2.805 mAh cm-2 ) and different formulated electrolytes. Our results suggest that the amount of LiH accumulation is negatively correlated with cyclability of practical LMBs. More importantly, we reveal a temperature sensitive equilibrium (Li + 1/2 H2 ⇌ LiH) governing formation and decomposition process of LiH at Li anode. We believe that the unusual understanding provided by this study will draw forth more insightful efforts to realize efficient Li protection and the ultimate applications of "holy grail" LMBs.

Improving Lithium-Sulfur Battery Performance under Lean Electrolyte through Nanoscale Confinement in Soft Swellable Gels.

Li-S batteries have been extensively studied using rigid carbon as the host for sulfur encapsulation, but improving the properties with a reduced electrolyte amount remains a significant challenge. This is critical for achieving high energy density. Here, we developed a soft PEO10LiTFSI polymer swellable gel as a nanoscale reservoir to trap the polysulfides under lean electrolyte conditions. The PEO10LiTFSI gel immobilizes the electrolyte and confines polysulfides within the ion conducting phase. The Li-S cell with a much lower electrolyte to sulfur ratio (E/S) of 4 gE/gS (3.3 mLE/gS) could deliver a capacity of 1200 mA h/g, 4.6 mA h/cm2, and good cycle life. The accumulation of polysulfide reduction products, such as Li2S, on the cathode, is identified as the potential mechanism for capacity fading under lean electrolyte conditions.

Biomechanical comparison of anatomical plating systems for comminuted distal humeral fractures.

PURPOSE: Six different mono-axial and poly-axial distal humeral plating systems with an anatomical plate design were compared. The aim of the biomechanical tests was to examine differences regarding system stiffness, median fatigue limit, and failure mechanisms. METHODS: Different configurations of two double plate fixation systems by two manufacturers for the treatment of complex distal humeral fractures (AO/OTA type C2.3) were biomechanically tested in a physiologically relevant setup. RESULTS: The 180° Stryker configuration presented itself as the system with the highest stiffness, being significantly stiffer (p < 0.001) than every system other than the poly-axial 180° aap system (p = 0.378). For the median fatigue limit the 180° Stryker and poly-axial aap systems were ranked first and second. The failure mechanism for all 90° systems was a fatigue breakage of the posterolateral plate. The 180° aap systems demonstrated breakage of the most distal screws of the lateral plate. The 180° Stryker system demonstrated screw breakage on both the medial and lateral plates. DISCUSSION: Breakage of the posterolateral plate as a failure mechanism for the 90° systems was expected. The 180° systems demonstrated a higher stiffness compared to the 90° constructs for the axial loading. In conclusion, both poly-axial anatomical plating systems provide sufficient stability in this scenario, and the 180° configurations demonstrated superior stiffness.

Good survivorship of all-polyethylene tibial component UKA at long-term follow-up.

PURPOSES: To determine the long-term survival rate of an all-polyethylene tibial unicompartmental knee arthroplasty (UKA) in a large series of consecutive patients and to investigate the possible factors that could influence the outcome. METHODS: A retrospective evaluation of 273 patients at 6-13 years of follow-up was performed. Clinical evaluation was based on KSS and WOMAC scores. Subjective evaluation was based on a visual analogue scale for pain self-assessment. Radiographic evaluation was performed to assess femoral-tibial angle (FTA), posterior tibial slope (PTS) and tibial plateau angle (TPA). A Kaplan-Meier survival analysis was performed assuming revision for any reason as primary endpoint. RESULTS: The 10-year implant survivorship was 87.6%. Twenty-five revisions (9.2%) were performed, and aseptic loosening of the tibial component was the most common failure mode (11 cases, 4%). The comparison of survival rate according to age at surgery did not show significant difference. Age at surgery, FTA, TPA and PTS were not related to higher risk of revision. No correlations were found between BMI, age at surgery and clinical scores. Finally, no statistical differences of radiographic measurements were found between revisions and non-revisions. CONCLUSIONS: The present study has demonstrated on a large series of patients that UKA with an all-polyethylene tibial component, with an accurate technique and a proper patient selection, can provide a satisfactory clinical and functional outcome and a good overall survivorship of the implant at long-term follow-up. These advantages could be achieved at a lower cost. LEVEL OF EVIDENCE: Retrospective Therapeutic Study, Level IV.

Compressive Mechanical Behavior and Corresponding Failure Mechanism of Polymethacrylimide Foam Induced by Thermo-Mechanical Coupling.

Thermal-mechanical coupling during the molding process can cause compressive yield in the polymer foam core and then affect the molding quality of the sandwich structure. This work investigates the compressive mechanical properties and failure mechanism of polymethacrylimide (PMI) foam in the molding temperature range of 20-120 °C. First, the DMA result indicates that PMI foam has minimal mechanical loss in the 20~120 °C range and can be regarded as an elastoplastic material, and the TGA curve further proves that the PMI foam is thermally stable within 120 °C. Then, the compression results show that compared with 20 °C, the yield stress and elastic modulus of PMI foam decrease by 22.0% and 17.5% at 80 °C and 35.2% and 31.4% at 120 °C, respectively. Meanwhile, the failure mode changes from brittle fracture to plastic yield at about 80 °C. Moreover, a real representative volume element (rRVE) of PMI foam is established by using Micro-CT and Avizo 3D reconstruction methods, and the simulation results indicate that PMI foam mainly shows brittle fractures at 20 °C, while both brittle fractures and plastic yield occur at 80 °C, and most foam cells undergo plastic yield at 120 °C. Finally, the simulation based on a single-cell RVE reveals that the air pressure inside the foam has an obvious influence of about 6.7% on the yield stress of PMI foam at 80 °C (brittle-plastic transition zone).

Investigation of the microscopic damage mechanisms in cotton fibers induced by mechanical friction.

For the problem of friction damage in cotton fiber processing, a multi-scale combination of investigation methods is proposed. The surface of damaged cotton fiber is detected by relevant test means with damage features such as dislocations, defects and cracks. The internal pyranose ring and glycosidic bond fail, the crystallinity decreases, and the number of hydrogen bonds decreases. Anisotropy exists in the frictional properties of the microscopic surface of the cotton fiber. The results of molecular dynamics simulation showed that the cellulose main chain failed mainly at the glycosidic bond, and the side chain failed mainly at the hydroxymethyl functional group. Its interchain hydrogen bond O3H…O5 was the least damaged. The cellulose crystal (200) surfaces had poor abrasion resistance, and the frictional properties of each crystal surface were anisotropic. The results of the study provide a theoretical basis for improving friction and wear problems in cotton fiber processing.

Experimental Investigation into the Failure Mechanisms of Fabric Membrane Materials with Defective Flat Round Cracks.

The emphasis of this study is placed on the investigation into the failure mechanisms of the fabric membranes when exposed to such defective cracks. This experimental study investigates the initial crack of a flat circle and conducts a uniaxial shear test on the membrane materials. The deformation of the membrane materials is obtained through an optical non-contact scanner. Our study has been conducted to assess the crack propagation of fabric membrane materials at different angles. The relationships between crack width and stress together with stress and strain are also obtained. Based on the results, a mechanic of failure on the membrane was proposed. Moreover, new findings into the ductility and energy absorption of the fabric membrane materials have been established to inform the failure mechanisms.

Bionic Design of High-Performance Joints: Differences in Failure Mechanisms Caused by the Different Structures of Beetle Femur-Tibial Joints.

Beetle femur-tibial joints can bear large loads, and the joint structure plays a crucial role. Differences in living habits will lead to differences in femur-tibial joint structure, resulting in different mechanical properties. Here, we determined the structural characteristics of the femur-tibial joints of three species of beetles with different living habits. The tibia of Scarabaeidae Protaetia brevitarsis and Cetoniidae Torynorrhina fulvopilosa slide through cashew-shaped bumps on both sides of the femur in a guide rail consisting of a ring and a cone bump. The femur-tibial joint of Buprestidae Chrysodema radians is composed of a conical convex tibia and a circular concave femur. A bionic structure design was developed out based on the characteristics of the structure of the femur-tibial joints. Differences in the failure of different joint models were obtained through experiments and finite element analysis. The experimental results show that although the spherical connection model can bear low loads, it can maintain partial integrity of the structure and avoid complete failure. The cuboid connection model shows a higher load-bearing capacity, but its failure mode is irreversible deformation. As key parts of rotatable mechanisms, the bionic models have the potential for wide application in the high-load engineering field.

Hierarchical Significance of Environment Impact Factor on the Sand Erosion Performance of Lightweight Alloys.

This paper addresses the challenge of ranking the factors that affect the erosion resistance of lightweight alloys, with a specific focus on aluminum alloys. A three-factor, four-level orthogonal experimental design was employed to examine the influence of various sand particle sizes, erosion speeds, and sand concentrations on the abrasion qualities of these alloys. Parameters such as mass loss, depth, residual stresses, and failure mechanisms were assessed to determine erosion performance. Analysis of variance (ANOVA) and regression analysis of the three key factors were performed. Our findings resulted in an erosion rate formula: erosion rate = 0.679 sand particle size +0.067 sand concentration -0.002 erosion velocity +0.285. Our findings indicate that particle size is the most significant factor affecting erosion rate, with sand concentration and erosion velocity being secondary factors. The failure mechanism reveals that larger sand particles tend to produce deeper slides, and higher sand concentrations result in an increased number of slides. A lower concentration leads to the appearance of erosion pits. And the test conditions of high concentration and low velocity lead to more serious brittle fractures of the substrate, often accompanied by the appearance of cracks.

A reliability estimation method based on combination of failure mechanism and ANN supported wiener processes.

For some engineering application, accurately estimating reliability only depend on the history data or failure mechanism is difficult to implement, due to the lack of data and imperfect theory of failure mechanism. Namely, both history data and failure mechanism should be utilized to improve the reliability estimation accuracy for engineering applications. Hence, we construct a reliability estimation method by fusing the failure mechanism and artificial neural network (ANN) supported Wiener processes for utilizing both history data and failure mechanism. ANN and failure mechanism are integrated into Wiener process with random effects, respectively. Bayesian model averaging (BMA) method is adapted to combine the failure mechanism with ANN supported Wiener processes, as well as to update the model parameters by fusing data. Based on a typical aviation hydraulic pump's actual dataset, we illustrate the advantages of our approach by comparing to Wiener process supported only by ANN or failure mechanism in engineering practices. The proposed method shows superiorities on reliability estimation considering the estimation accuracies comparing the other two models.

Failure Mechanism Analysis and Emerging Strategies for Enhancing the Photoelectrochemical Stability of Photoanodes.

The development of efficient and stable photoanode materials is essential for driving the possible practical application of photoelectrochemical water splitting. This article begins with a basic understanding of the fundamentals of photoelectrochemical devices and photoanodes. State-of-the-art strategies for designing photoanodes with long-term stability are highlighted, including insertion of hole transport layers, construction of protective/passivation layers, loading of co-catalysts, construction of heterojunctions, and modification of the electrolyte. Based on the insights gained from these effective strategies, we present an outlook for addressing key aspects of the challenges of stabilizing photoanodes development in the future work. Widespread adoption of stability assessment criteria will facilitate reliable comparisons of results from different laboratories. In addition, deactivation of photoanode is defined as a 50 % reduction in productivity. An in-depth understanding of the deactivation mechanism is essential for the design and development of efficient and stable photoanodes. This work will provide insights into the stability assessment of photoanode and facilitate the production of practical solar fuels.