Void Defects Research Articles

Residual Stresses and Micro-voids Propel Metal Diffusion for Filament-Based Memristors.

Metal filamentation based mechanisms have the advantage of a high switching current ratio, yet typically require high switching voltages to activate the memristive device due to the primary mechanism of atomic vacancy filling and movement. Herein, Introducing non-reactive nitrogen gas during plasma sputtering of silver is shown to prime the overlying metal nitride layer to achieve low threshold switching at applied biases of below 60 millivolts. Residual nitrogen species within the silver under-layer promote the creation of nano-sized void defects within the superjacent dielectric layer, which, coupled with residual stresses in the gigapascal range, enable sub-micron filamentation growth. These memristor devices function similarly to potassium ion channels, displaying current growth and relaxation patterns that align with the Hodgkin-Huxley model, and as such are amenable to the development of artificial neuron structures. Further, a diverse set of neuromorphic behaviors not seen within typical metal filamentation based memristors is observed. This includes multi-peak synaptic weight changes in the device's response to spiked stimuli. Both the switching voltages and neuromorphic properties are linked to the nitrogen-argon pressure during silver deposition. Interestingly, these devices also exhibit lateral growth of silver filamentation across the surface of the metal nitride thin film layer with gaps of more than a hundred micrometers, suggesting that the underlying silver undergoes accumulation and breakthrough. The filling of large micro-voids with Ag generates large nanoparticles that easily propagate, enabling a large diffusion front and faster filamentation time, whereas small micro-voids create a bottleneck in the filamentation process. Additionally, the introduction of residual stresses in conventional diffusion theory indicates greater dendritic interconnectivity and thus electrode to electrode connection. This study demonstrates that the facile incorporation of non-reactive gases during the sputter-deposition of a metal electrode opens a path to unique material mechanisms that facilitate the development of versatile memristors.

Research on dynamic indicators for void defect detection in rectangular cross-section CFST columns

ABSTRACT This study aims to address potential internal void defects in rectangular cross-section concrete-filled steel tube (CFST) columns. A CFST internal void defect detection method based on vibration testing and modal analysis is proposed, with three dynamic indicators constructed from modal parameters for CFST void detection, including absolute difference of the diagonal gaussian curvature of the flexibility matrix, the gaussian curvature of the absolute diagonal flexibility difference, and the Bayesian fusion indicator. Indoor experiments were conducted using CFST specimens with and without internal voids, applying excitation with a shaker and capturing vibration response signals using a laser Doppler vibrometer. Modal parameters were obtained through modal analysis to validate indicators effectiveness. Further on-site experiments were conducted, and modal parameters under various void conditions and loading scenarios were obtained via finite element simulation, verifying the effectiveness of the indicators. Experimental results demonstrate that these indicators can effectively locate and identify cm-level internal void defects in CFST structures, with the Bayesian fusion indicator performing most effectively. This study validates the feasibility of dynamic indicators in CFST void defect detection, providing theoretical support and experimental data for this field.

A review of 3D printing continuous carbon fiber reinforced thermoplastic polymers: Materials, processes, performance enhancement, and failure analysis

AbstractFused filament fabrication (FFF) technology, recognized as a leading 3D printing method for the production of continuous carbon fiber reinforced thermoplastic polymer (CCFRTP) components, has garnered significant attention due to its design flexibility, independence from molds, and capability for rapid prototyping of complex structures. This paper presents a comprehensive analysis and review of the challenges associated with enhancing mechanical properties stemming from interfacial bonding issues and pore defects in 3D‐printed CCFRTP parts. Specifically, this study thoroughly examines the properties and modification techniques pertinent to two critical constituents of printing materials: the resin matrix and carbon fiber reinforcement. It also explores advancements in FFF printing equipment specifically designed for CCFRTP components, alongside current developments in related impregnation processes. Furthermore, this work introduces an evolution in continuum path planning grounded in principles of structural lightweight design while applying topology optimization to create anisotropic CCFRTP structures. The influence of various printing process parameters on mechanical properties is analyzed systematically; additionally, processing strategies that incorporate auxiliary reinforcement techniques—such as thermopressure, negative pressure, laser application, magnetic fields, microwave energy, and infrared radiation—are emphasized. The mechanical behavior is meticulously tracked throughout the study, while corresponding failure mechanisms are scrutinized through recent advancements in characterization methods aimed at visualizing void defects. We critically assess the existing technological challenges that impede the 3D printing of CCFRTPs and propose potential future research directions intended to inspire further exploration within this promising field.Highlights Optimizing the CCFRTP interface hinges on material matching and synergistic CCF mods. CF continuity and anisotropy demand refined print/impregnation design and algorithm. Stress‐guided path planning with topo optimization unveils innovative potential. Optimized print parameters and ancillary processes facilitate enhanced performance. 3D characterization ensures reliable material void and process defect assessment.

Mitigation of Sink Voids in Thick-Walled Thermoplastic Components via Integrated Taguchi DOE and CAE Simulations.

A gauge plate is a typical thick-walled injection-molded component featuring a complex construction used in high-speed railways, and it is prone to sink voids during the injection process. It is difficult to obtain a void-free injection molded part due to uneven cooling-induced localized thermal gradients, crystallization shrinkage of semicrystalline thermoplastics, fiber orientation-induced anisotropic shrinkage, injection parameter-dependent fountain flow, and inconsistent core compensation. This work employed design of experiment (DOE) and computer-aided engineering (CAE) simulations to analyze the influence of injection parameters on the volumetric shrinkage of the gauge plate and to identify the optimal injection process. A Taguchi orthogonal array L9 was applied, in which four injection molding process parameters were varied at three different levels. The fundamental causes of sink void defects in the gauge plate were then examined via MoldFlow analysis on the basis of the optimized injection parameters. The MoldFlow study indicates a high probability of the presence of sink void defects in the injection-molded gauge plate. To minimize sink void defects, a structural optimization design of the gauge plate was implemented to achieve a more uniform wall thickness, and the advantages of this optimization were demonstrated via comparative analysis. The small batch production of the injection-molded gauge plates demonstrates that the optimized gauge plate shows no sink voids, ensuring consistent quality that adheres to the engineering process and technical specifications.

Understanding the Deformation and Fracture Behavior of β−HMX Crystal and Its Polymer−Bonded Explosives with Void Defects on the Atomic Scale

Understanding the Deformation and Fracture Behavior of β−HMX Crystal and Its Polymer−Bonded Explosives with Void Defects on the Atomic Scale

High-Performance Nacre-Inspired 2D Carbon-Based Nanocomposites.

Nacre has become the golden standard for the structural design of high-performance composites due to extraordinary fracture toughness, which exceeds the mixing principle of traditional composites by two orders of magnitude. Surprisingly, the unique biomaterials are formed under ambient temperature and pressure conditions, resulting in low energy consumption and no pollution. It is an effective approach to obtain inspiration from structure-activity relationships of biomaterials for developing the next-generation of high-performance composites. Furthermore, 2D carbon nanomaterials, such as graphene and MXene, having exceptional mechanical and electrical properties, are ideal candidates for fabricating new generation high-performance composites that would replace carbon fiber (CF) composites. This review systematically summarizes relevant works for high-performance 2D carbon nanocomposites (TDCNs) inspired by nacre. The review first explores structural insights from the nacre. Next, the fabrication strategies of TDCNs are systematically summarized, with an emphasis on achieving highly aligned 2D carbon nanosheets through advanced assembly techniques. Subsequently, the critical role of void defects, which is a key factor governing the mechanical properties of TDCNs, is addressed by analyzing their formation mechanisms, characterization methodologies, and elimination strategies. Finally, the applications and challenges of high-performance TDCNs obtained through highly aligned assembly and densification processes are discussed.

Study on imaging techniques and quantitative detection method for internal void defects in rubber based on terahertz reflection imaging.

This paper applies the reflection mode of terahertz time-domain spectroscopy technology to conduct research on the void defects in black silicone rubber samples. Algorithms such as power spectral density (PSD) integration imaging, homomorphic filtering, and the Otsu method are innovatively integrated to construct an efficient, high-precision defect characterization system. Different from traditional research, this paper deeply explores the advantages of each algorithm and optimizes them according to the characteristics of rubber materials and terahertz signals. By combining multiple features in the time-domain and frequency-domain to reconstruct terahertz images, and with the collaborative optimization of grayscale histogram equalization and filtering algorithms on the imaging quality, the optimal combination of PSD integration imaging, homomorphic filtering, and the Otsu method is determined, achieving precise defect imaging and quantification. In spectral analysis, a method combining wavelet signal denoising and time-domain spectroscopy is proposed. A formula based on time-of-flight was then used for quantitative analysis of the defects. In 3D imaging, an innovative alignment operation of denoised time-domain spectral curves is introduced. Combined with the maximum intensity projection, the clear visualization of void defects is realized.

Regulation of interfacial intermetallic compounds growth and void defect formation in Sn-9Zn-0.02Al/Cu solder joint by balancing interfacial elemental diffusion: An effect of Pt alloying

Regulation of interfacial intermetallic compounds growth and void defect formation in Sn-9Zn-0.02Al/Cu solder joint by balancing interfacial elemental diffusion: An effect of Pt alloying

Simulation Study on the Effect of Temperature on PD Inside Void Defect Under the Closed Condition

Simulation Study on the Effect of Temperature on PD Inside Void Defect Under the Closed Condition

Suppression of Multiple Reflection Interference Signals in GPR Images Caused by Rebar Using VAE-GAN

Due to the rebars layer’s shielding effect on Ground Penetrating Radar (GPR) waves, the hyperbolic clutter generated by the rebars interferes with the echoes from void beneath them. The overlapping waveforms of both signals result in attenuation and distortion of the void signals, making it difficult to identify void defects under the rebar. This study proposes an unsupervised generative network model based on Variational Autoencoders (VAEs) and Generative Adversarial Networks (GANs). Through a shared latent space, mapping is achieved between two image domains, effectively eliminating the multiple reflection interference signals caused by the rebar while accurately reconstructing the void defects, generating GPR B-Scan images without rebar clutter. Additionally, the channel and spatial attention module (CSA) is implemented into the model to help the network to better focus on the essential information in GPR images. The proposed model was validated through ablation and comparative experiments using synthetic data. Finally, real GPR data from the Husa Tunnel were used to verify the model’s effectiveness in practical engineering applications. The results showed that this model is highly effective; it improves the visibility of void defects signals, thereby enhancing the interpretability of GPR data for tunnel lining inspections.

Modelling and simulation of TSV considering void and leakage defects

Modelling and simulation of TSV considering void and leakage defects

Utility and influence mechanism of densification modulation on grain boundary diffusion in NdFeB magnets

Utility and influence mechanism of densification modulation on grain boundary diffusion in NdFeB magnets

Mechanical characterization of 3D printed multiscale carbon nanofiller/continuous fiber reinforced polymer hybrid composites

AbstractMechanical properties of 3D printed continuous fiber reinforced polymer composites (CFRPCs) are generally lower than expected due to unavoidable voids and weak interfacial adhesion. However, previous research work has rarely been reported on introducing carbon nanofillers such as carbon nanotubes (CNTs) and graphene oxide (GO) to reduce internal void defects and improve interfacial adhesion of CFRPCs. In this work, an innovative means of introducing CNTs and GO is proposed to reduce internal void defects and improve interfacial adhesion for enhancing the mechanical properties of 3D printed hybrid CFRPCs. Polyethylene terephthalate glycol (PETG) is employed as a polymer matrix due to its excellent processability for the 3D printing process. Continuous basalt fiber (CBF) is selected as a microscale filler due to its high mechanical properties, low cost and availability for additive manufacturing. It is shown that introducing carbon nanofillers into PETG leads to notably reduced porosity and greatly improved interfacial adhesion between CBF and PETG. As a result, the mechanical properties of 3D printed hybrid CFRPCs are significantly enhanced by introducing carbon nanofillers into the polymer matrix. Finally, the mechanisms of CNTs and GO are analyzed for enhancing the mechanical properties of 3D printed hybrid CFRPCs. The multiscale filler enhancement method has the characteristics of low cost and easy implementation. This approach contributes a novel idea for preparing high‐performance 3D printed CFRPCs by reducing internal void defects and enhancing interfacial adhesion by simply introducing carbon nanofillers. This method can expand material systems and provide a new development idea for industrial applications.Highlights Proposed a new means to improve the mechanical properties of 3D printed CFRPCs. The performances of PETG composites are enhanced by optimal CNT or GO content. Combination of carbon nanofillers with PETG enhances interfacial adhesion.

Selbstorganisation von ZIF‐8‐Nanopartikeln zu “Brick‐and‐Mortar”‐Membranen für die Wasserstofftrennung durch ein Zink‐Koordinations‐Polymer

AbstractDie MOF (metal‐organic framework) Struktur ZIF‐8 (zeolitic imidazolate framework) besitzt eine vergleichsweise hohe Stabilität und permanente Porosität mit einem kristallographischen Porendurchmesser von 3,4 Å, was sie daher zu einem vielversprechenden Kandidaten für Wasserstoff‐Trennmembranen macht. Die meisten polykristallinen ZIF‐8‐Membranen weisen jedoch eine geringe H2/CO2‐Mischgas‐Selektivität (kinetische Durchmesser von 2,9/3,3 Å) auf, was auf die interkristallinen Strukturdefekte und zusätzlich auf die Gerüstflexibilität der ZIF‐8‐Struktur mit einer theoretischen Aperturgröße von 3,4 Å zurückzuführen ist. Inspiriert von der “Brick‐and‐Mortar”‐Struktur von Perlmutt entwickeln wir hier eine Mixed Matrix Membran, bei der kristalline ZIF‐8‐Nanopartikel (Ziegel) durch ein ultradünnes Zink‐Koordinationspolymer als Zwischenschicht (Mörtel) miteinander durch Selbstorganisation verbunden sind. Durch Koordinationsbindungen zwischen Zn2+ und verzweigtem Polyethylenimin (PEI) wird ein Zink‐Koordinationspolymer‐Netzwerk gebildet. Die Zn2+‐Ionen dieses Koordinationspolymers treten in starke Wechselwirkung mit den terminalen Oberflächen‐OH‐Gruppen der ZIF‐8‐Nanopartikel, wodurch interkristalline Defekte in Form von Hohlräumen eliminiert werden. Insbesondere die Transportwege durch das Koordinationspolymer aber auch durch die ZIF‐8‐Kristalle sind H2‐selektiv. Die ZIF‐8‐PEI‐Mixed Matrix Membran zeigt einen schnellen und hochselektiven Wasserstofftransport: Die H2‐Permeabilität beträgt ~1,8×105 Barrer und die H2/CO2‐Selektivität des Mischgases 176, was den Stand der Technik weit übertrifft. Diese bioinspirierte multifunktionale Membran erweitert den Anwendungsbereich von Molekularsiebmembranen.

Zinc Coordination-Polymer-Mediated Self-Assembly of Nanoparticles into "Brick-and-Mortar" Membranes for Hydrogen Separation.

Zeolitic imidazolate framework-8 (ZIF-8) with high stability and porosity is a promising candidate for hydrogen separation membranes. However, most ZIF-8 polycrystalline membranes exhibit low H2/CO2 (kinetic diameters of 2.9/3.3 Å) mixed gas selectivity, due to the intercrystalline defects and the unprecise molecular sieving originated from framework flexibility of ZIF-8 structure with a theoretical aperture size of 3.4 Å. Here, inspired by nacre's "brick-and-mortar" structure, we develop mixed matrix type composite membranes in which dominant crystalline ZIF-8 nanoparticles (bricks) are interconnected by ultrathin zinc coordination polymer interlayers (mortar) via self-assembling. Driven by coordination bonds between Zn2+ from precursor colloid and branched polyethyleneimine (PEI), a zinc coordination polymer network is formed to connect ZIF-8 nanoparticles through interactions between Zn2+ of coordination polymer and surface terminal groups on ZIF-8 nanoparticles, thus eliminating intercrystalline void defects and providing a highly selective H2 transport pathway. Meanwhile, the micropores and large cavities in ZIF-8 allow fast H2 transport. Benefitting from both highly selective pathway and fast H2 transport through porous ZIF-8, the optimized ZIF-8-PEI membrane exhibits a record-high H2 permeability of ~1.78×105 Barrer with a high mixed gas H2/CO2 selectivity of 176, surpassing state-of-the-art performance. This bioinspired multifunctional membrane expands the scope of molecular sieving membrane.

Optimising process parameters for enhanced performance in PLA-based fused filament fabrication: A multi-objective approach

Manufacturing technologies, particularly additive manufacturing (AM), have ushered in innovative practices for complex part production, prominently exemplified by fused filament fabrication (FFF) for the production of complex parts. Significant efforts have been ongoing with a focus on improving performance measures of biodegradable bioplastics, notably polylactic acid (PLA), within the eco-conscious packaging industry. Findings in this field have given rise to FFF technologies for enhancing critical performance measures such as surface roughness (Ra) of food packaging by investigating optimal process parameters such as layer thickness, raster width, raster angle, printing speed, air gap and bed temperature, to name but a few. Additional performance measures affecting geometric part quality, such as thickness variations along horizontal and vertical geometric planes, have been analysed in previous studies to derive solutions for enhancing the correlation between process parameter input and dimensional accuracy. Despite these advancements, research on 3D-printed specimens has typically focused on manufacturing standards with thickness greater than 1 mm, as opposed to the thinner requirements of some plastic packaging products. This practice has left a gap of uncertainty regarding the potential mechanical performance of thin-film 3D-printed products for current and future applications. The necessity to induce fewer infill layers during the FFF process has sparked interest in evaluating the efficacy of process parameters in achieving reliable mechanical performance in surface quality and Z-axial dimensional accuracy compared to conventionally manufactured plastic products. This article, therefore, sought to address this uncertainty using a design of experiments (DoE) approach followed by multi-objective optimisation through the application of genetic algorithm (GA) techniques. From these efforts, optimal process parameters of layer thickness (0.151 mm), raster width (0.514 mm) and raster angle (82.75o) for the minimisation of Ra and Delta-Z (∇Z) variation in PLA-based FFF specimens. Further data analysis noted variability in the accuracy of Ra predicted R² values depending on the raster angle and void defects at the surface layer, while additional observations indicated an increase in Z-axial variation when a layer thickness of 50% of the overall specimen thickness was utilised. This study concluded by underscoring the necessity for future research in integrating multi-objective optimisation further, with the aim of not only improving the predictability of process parameter optimisation but also the detection, analysis and minimisation of defects using machine learning tools and techniques.

Reinforcement of Carbazole-Based Self-Assembled Monolayers in Inverted Perovskite Solar Cells.

Self-assembled monolayers (SAMs) with excellent hole conduction capabilities significantly improve the performance of inverted perovskite solar cells (PSCs). However, the amphiphilic nature of SAMs causes the spontaneous formation of spherical micelles in solution, limiting their surface coverage and uniformity on indium tin oxide (ITO) substrates. Furthermore, the distribution of the SAMs directly affects the morphology of perovskite films and the charges transfer properties at the buried interface. This study employs a cosolvent strategy combining n-butanol and dimethyl sulfoxide to improve the uniform spreading of SAMs on ITO. The synergistic interaction between the solvent molecules smooths the surface of [2-(3,6-dimethoxy-9H-carbazol-9-yl) ethyl] phosphonic acid (MeO-2PACz) and enhances its surface coverage. The cosolvent based MeO-2PACz has the characteristics of concentrated surface potential distribution and high work function, exhibiting uniform and enhanced P-type behavior. Additionally, the cosolvent-treated SAMs provide uniform nucleation sites for the crystallization of perovskite, effectively eliminating void defects at the buried interface and improving the crystallinity of perovskite films. Consequently, the optimized device achieves a power conversion efficiency (PCE) of 25.51% and a fill factor of 84.38%. Furthermore, the ordered SAMs improve the stability of PSCs, with encapsulated device retaining 92.63% of its initial PCE after operating for 1500 h under simulated AM 1.5G standard irradiation in air at 65 °C.

Morselized Femoral Head Impaction Bone Grafting of Large Defects in Ankle and Hindfoot Fusions.

Ankle and hindfoot fusion in the presence of large bony defects represents a challenging problem. The purpose of this study was to evaluate outcomes of patients who underwent ankle-hindfoot fusions with impaction bone grafting (IBG) with morselized femoral head allograft to fill large bony void defects. This was a 3-center, retrospective review of a consecutive series of 49 patients undergoing ankle or hindfoot fusions with femoral head IBG for filling large bony defects. Union was assessed clinically and radiologically with radiography or computed tomography. Graft stability/collapse was identified on radiographs as loss of graft height across the fusion interface. Indications included 35 failed total ankle arthroplasty, talar osteonecrosis and collapse (7 patients), failed ankle fusion (4 patients), trauma with bone loss or fracture nonunion (1 patients), and other (2 patients). Tibiotalocalcaneal (TTC) fusion was performed in 36 (73%) patients and ankle (TT) fusion in 13 (27%). Mean age was 59.3 (19-78) years. Mean follow-up was 22.9 ± 8.3 months. Eighteen percent were smokers. Mean depth of the bone defect was 35.2 ±8.7 mm, and mean volume of the defect was 62.2 ±5.8 cm3. Symptomatic nonunion rate was 14% (7/49). The mean time to radiologic union was 7.6 ±3.2 months. Complete radiologic union rate occurred in 73% (36/49). Eight TTC fusion patients (22.2%) united at the tibiotalar joint but not at the subtalar joint, of which 6 were asymptomatic. There was no graft collapse, even in patients developing nonunion, with all patients maintaining bone incorporation and leg length. Impaction of morselized femoral head allograft can fill large bony voids around the ankle or hindfoot during fusion, with rapid graft incorporation and no graft collapse despite early loading. This technique offers satisfactory and comparable union outcomes without limb shortening or expensive custom 3D-printed metal cages.

Dynamic analysis of water-rich heavy haul railway tunnels considering basement defects evolution and train effects

With the rapid development of heavy haul railway transportation technology, tunnel foundation defects and their effects on structural performance have attracted wide attention. This paper systematically investigates the evolution mechanism of tunnel foundation defects in heavy haul railway tunnels and their impact on structural stiffness degradation through experiments and numerical simulations. A heavy haul train–ballasted track–tunnel basement–surround rock dynamic interaction model (TTTR model) is constructed. Firstly, the study reveals the four-stage evolution process of initial defects in the tunnel basement under complex environmental conditions. Experiments were conducted to measure the load-bearing capacity and stiffness degradation of the tunnel basement structure under different defect states. It is found that foundation defects, especially under the coupling of loose fill in the basement with the water-rich environment of the surrounding rock, significantly reduce the stiffness of the tunnel bottom structure and increase the risk of structural damage. Then, based on refined simulation of wheel–rail interaction and multi-scale coupled modeling technology, the TTTR dynamic interaction model was successfully constructed, and its validity was proven through numerical validation. A time-varying coupling technique of constrained boundary substructures (CBS technique) was adopted, significantly improving computational efficiency while ensuring calculation accuracy. The study also analyzes the effects of different degrees of void defects on the dynamic behavior of the train and the dynamic characteristics of the tunnel structure. It finds that foundation defects have a significant impact on the train’s operational state, track vibration displacement, and vibration stress of the tunnel lining structure, especially under the coupling effect of basement voids and the water-rich environment, which has the greatest impact. The research results of this paper provide a theoretical basis and technical support for the maintenance and reinforcement of tunnel foundation structures.

Buried interface management toward high-performance perovskite solar cells.

The interface between the perovskite layer and the electron transport layer is an extremely important factor that cannot be ignored in achieving high-performance perovskite photovoltaic technology. However, the void defects of the interface pose a serious challenge for high performance perovskite solar cells (PSCs). To address this, we report a polydentate ligand reinforced chelating strategy to strengthen the stability of the buried interface by managing interfacial defects and stress. Gelatin-coupled cellulose (GCC) is employed to manipulate the buried interface. The unique functional groups in GCC synergistically passivate the defects from the surface of SnO2 and the bottom surface of the perovskite layer. Our work demonstrates that by implementing GCC as a buried interface strategy, it is possible to prepare devices with reduced vacancy states, non-radiative recombination suppression, and excellent optoelectronic performance. At the same time, this work improves the efficiency and stability of PSCs and provides greater space for device manufacturing.