Press Conduction Welding for Secondary Bonding of Aircraft Skin/Stiffener Assemblies Using Carbon Fiber/PEKK Thermoplastic Composites and PEI Adhesive.

This study investigates the secondary bonding of aircraft skin/stiffener assemblies using press conduction welding with carbon fiber/polyetherketoneketone thermoplastic composites and polyetherimide adhesive. Recognizing the challenges posed by conventional welding methods in maintaining material integrity and uniformity, this research explores an alternative methodology that mitigates these issues while ensuring high-strength bonds. The press conduction welding parameters were selected based on single-lap shear tests and applied in the bonding of skin and omega stiffener components. The temperature range was determined using differential scanning calorimetry. The pressure was held at 1 MPa for 180 s. The welding temperature that produced a high-bonding strength was identified experimentally; these key variables were then used in the welding process of the skin and omega stiffener. By analyzing how the fibers tear and the effectiveness of interdiffusion between the plies, we were able to gain insights into the bonding strength and fractured surface. The findings suggest that press conduction welding provides a viable route for secondary bonding in thermoplastic composite structures, highlighting its advantages in terms of processing efficiency and integrity. This study contributes to the understanding of the mechanical behaviors of bonded joints and underscores the significance of temperature control in the welding process.

Spring-In Prediction of CFRP Part Using Coupled Analysis of Forming and Cooling Processes in Stamping.

The spring-in phenomenon of the composite parts can affect the assembly process. This study aims to predict the spring-in phenomenon of a carbon fiber reinforced plastic (CFRP) part. Here, we predict the spring-in of the CFRP part using a coupled analysis of the forming and cooling processes during the stamping process. First, a simulation of the entire forming process, such as the transfer of the composite laminate, gravity analysis, and forming was performed to obtain the temperature distribution of the CFRP part. Subsequently, a finite-element (FE) simulation of the cooling process was conducted to predict the spring-in phenomenon of the shaped CFRP part using the temperature data obtained in the forming simulation. Finally, a CFRP part was manufactured and compared with the results of the FE simulation.

A State-of-the-Art Review on Advanced Joining Processes for Metal-Composite and Metal-Polymer Hybrid Structures.

Multi-materials of metal-polymer and metal-composite hybrid structures (MMHSs) are highly demanded in several fields including land, air and sea transportation, infrastructure construction, and healthcare. The adoption of MMHSs in transportation industries represents a pivotal opportunity to reduce the product's weight without compromising structural performance. This enables a dramatic reduction in fuel consumption for vehicles driven by internal combustion engines as well as an increase in fuel efficiency for electric vehicles. The main challenge for manufacturing MMHSs lies in the lack of robust joining solutions. Conventional joining processes, e.g., mechanical fastening and adhesive bonding involve several issues. Several emerging technologies have been developed for MMHSs' manufacturing. Different from recently published review articles where the focus is only on specific categories of joining processes, this review is aimed at providing a broader and systematic view of the emerging opportunities for hybrid thin-walled structure manufacturing. The present review paper discusses the main limitations of conventional joining processes and describes the joining mechanisms, the main differences, advantages, and limitations of new joining processes. Three reference clusters were identified: fast mechanical joining processes, thermomechanical interlocking processes, and thermomechanical joining processes. This new classification is aimed at providing a compass to better orient within the broad horizon of new joining processes for MMHSs with an outlook for future trends.

Stress Analyses of Retrograde Cavity Preparation Designs for Surgical Endodontics in the Mesial Root of the Mandibular Molar: A Finite Element Analysis-Part II.

INTRODUCTION: The aim of this study was to investigate the influence of apical filling material and the modification made to the apical preparation design in surgical endodontics on the areas of stress concentration in the mesial root of a mandibular molar using finite element analysis. METHODS: The filling material was injected under 2 conditions (ie, with or without mineral trioxide aggregate retrograde filling). The apical preparation design was modified by extending the preparation mesially while maintaining a similar prepared area. We contained the displacement of all the nodes at the base of the supporting bone and applied a force of 150 N to the vertical axis. We analyzed stress generation and concentrations numerically for all cavity design groups. RESULTS: In the presence of retrograde filling, the von Mises stress decreased gradually according to the enlargement of the prepared cavity in the subgroups. When the retrograde filling was absent, the von Mises stress increased as the prepared cavity enlarged. The modification of the apical preparation extending in the mesial direction showed a drastic decrease in stress concentration. CONCLUSIONS: Within the limitations of this study, it was advantageous to perform mesial retrograde preparation within the mesial root dentin to maintain a balanced root dentin on both sides of the apical preparation and create a low-stress field. The surgeon should be careful not to wash out or dislodge the retrograde filling material during obturation to avoid failure of surgery.

Comparison of Screw-In Forces during Movement of Endodontic Files with Different Geometries, Alloys, and Kinetics.

This study compared the maximum screw-in forces of various instruments during their movements. Forty simulated canals in resin blocks were randomly divided into four groups (n = 10): ProTaper Universal F2, ProTaper Gold F2, WaveOne Primary, and WaveOne Gold Primary. To standardize a lumen size, all artificial canals were prepared with ProTaper Universal F1. The rotation speed was set at 350 rpm with an automated 4 mm pecking motion at a speed of 1 mm/s. The pecking depth was increased by 1 mm for each pecking motion until the file reached the working length. During instrumentation, screw-in forces were automatically recorded by customized software. Maximum screw-in forces were analyzed by one-way ANOVA and Tukey's post hoc comparison with the significance level at 0.05. WaveOne Gold files generated the lowest maximum screw-in forces, followed by ProTaper Gold, WaveOne, and ProTaper Universal (p < 0.05). Under the condition of this study, heat-treated nickel-titanium (NiTi) files with smaller cross-sectional area, fewer contact points, and reciprocating movements resulted in a lower screw-in effect.

Stress Analyses of Retrograde Cavity Preparation Designs for Surgical Endodontics in the Mesial Root of the Mandibular Molar: A Finite Element Analysis-Part I.

INTRODUCTION: The aim of this study was to investigate the influence of various apical preparation designs for surgical endodontics on stress concentrations in the mesial root of the mandibular molar under different experimental conditions using finite element analysis. METHODS: We designed 2 apical preparation groups according to whether an isthmus was present or not. Each group contained 4 subgroups according to the size of the apical preparation. We constrained the displacement of all nodes at the base of the supporting bone and applied a force of 150 N to the vertical axis. We analyzed stress generation and concentrations numerically for the groups and subgroups. RESULTS: In the subgroups, the von Mises and maximum principal stresses reduced gradually according to the enlargement of the prepared cavity. However, when the preparation extended excessively in the isthmus preparation groups, the situation reversed (ie, both von Mises and maximum principal stresses increased). CONCLUSIONS: Within the limitations of this study, the apical preparation design influenced the distribution of stress concentration. Unlike the overall pattern in which stress decreased as the amount of apical preparation increased, stress increased when the amount of residual dentin was extremely thin.

The geometric effect of an off-centered cross-section on nickel-titanium rotary instruments: A finite element analysis study.

BACKGROUND/PURPOSE: Geometric design dictates the mechanical performance of nickel-titanium rotary instruments. Using finite element (FE) analysis, this study evaluated the effects of an off-centered cross-sectional design on the stiffness and stress distribution of nickel-titanium rotary instruments. MATERIALS AND METHODS: We constructed three-dimensional FE models, using ProTaper-NEXT type design (PTN) as well as three other virtual instruments with varied cross-sectional aspect ratios but all with the same cross-sectional area. The cross-sectional aspect ratio of the PTN was 0.75, while others were assigned to have ratios of 1.0 (square), 1.5 (rectangle), and 2.215 (centered-rectangle). The PTN center of the cross-section was 'k', while others were designed to have 0.9992k, 0.7k, and 0 for the square, rectangle, and centered-rectangle models, respectively. To compare the stiffness of the four FE models, we numerically analyzed their mechanical response under bending and torque. RESULTS: Under the bending condition, the square model was found to be the stiffest, followed by the PTN, rectangle, and then the centered-rectangle model. Under the torsion, the square model had the smallest distortion angle, while the rectangular model had the highest distortion angle. CONCLUSION: Under the limitation of this study, the PTN type off-centered cross-sectional design appeared the most optimal configuration among the tested designs for high bending stiffness with cutting efficiency while rotational stiffness remained similar with the other designs.

Effects of Pitch Length and Heat Treatment on the Mechanical Properties of the Glide Path Preparation Instruments.

INTRODUCTION: This study aimed to compare the effects of pitch length and heat treatment on the mechanical properties of glide path establishing instruments. METHODS: Prototypes of glide path preparation files (#14/.03 taper) were made to evaluate the effects of different pitch lengths and heat treatments. The files were divided into 4 groups according to the pitch length (pG and OneG) and heat treatment (pGH and OneGH). For the torsional resistance test, ultimate strength and fracture angle were measured, and the file tip was fixed at 3 different levels of 2, 4, and 6 mm from the tip (n = 10 for each level). The toughness was calculated by multiplying the ultimate strength and the fracture angle. The cyclic fatigue resistance was compared by measuring the number of cycles to fracture in a curved metal canal (n = 10). The screw-in forces were measured during instrumentation motions with a sequential increase in the pecking distance of 1 mm until the file reached the end of the simulated resin canal (n = 10). RESULTS: The heat-treated groups showed lower toughness and higher cyclic fatigue resistance than the non-heat-treated groups. The short pitch groups showed significantly higher torsional strengths than the long pitch groups. The heat-treated groups had significantly lower screw-in forces than the non-heat-treated groups. CONCLUSIONS: Under the limitations of this study, the torsional strength of the experimental file was reduced by heat treatment and increased by the short pitch length. Thus, a non-heat-treated file with a shorter pitch length would be favorable as a rotary glide path instrument.

Galactosylated magnetic nanovectors for regulation of lipid metabolism based on biomarker-specific RNAi and MR imaging.

The specific delivery of ribonucleic acid (RNA) interfering molecules to disease-related cells is still a critical blockade for in vivo systemic treatment. Here, this study suggests a robust delivery carrier for targeted delivery of RNA-interfering molecules using galactosylated magnetic nanovectors (gMNVs). gMNVs are an organic-inorganic polymeric nanomaterial composed of polycationics and magnetic nanocrystal for delivery of RNA-interfering molecules and tracking via magnetic resonance (MR) imaging. In particular, the surface of gMNVs was modified by galactosylgluconic groups for targeted delivering to asialoglycoprotein receptor (ASGPR) of hepatocytes. Moreover, the small interfering RNAs were used to regulate target proteins related with low-density lipoprotein level and in vivo MR imaging was conducted for tracking of nanovectors. The obtained results show that the prepared gMNVs demonstrate potential as a systemic theragnostic nanoplatform for RNA interference and MR imaging.

Geometric optimization for development of glide path preparation nickel-titanium rotary instrument.

INTRODUCTION: This study was done to develop a glide path preparation nickel-titanium rotary instrument by size optimization procedures and evaluate the properties of the prototype. METHODS: G-1 and G-2 files were tested for cyclic fatigue, torsional resistance, and screw-in force. The cyclic fatigue resistance was compared by measuring the number of cycles to failure by using a 90° curved metal canal (n = 10). The torsional resistance was evaluated at 3 levels (2, 4, and 6 mm from the file tip) by measuring the ultimate torsional load (n = 10 each level). The screw-in forces (n = 5) were measured during sequential pecking in a simulated resin block to the end of foramen by using the customized shaping device (AEndoS). Meanwhile, finite element models of G-1 and G-2 files were made by reverse engineering, and their bending stiffness and torsional properties were calculated. By analyzing the results from mechanical tests and finite element analysis, a universal G (uG) file was designed to have intermediary mechanical properties, and then the prototype was fabricated by the manufacturer. Cyclic fatigue and torsional resistance tests and screw-in force with the uG were compared with G-1 and G-2 files. RESULTS: The prototype of uG file showed higher cyclic fatigue resistance than the G-2 file and intermediary torsional strength and screw-in forces between the G-1 and G-2 files. CONCLUSIONS: The prototype production from a size optimization procedure produced appropriate mechanical properties for the purpose of development.

Stress generation during self-adjusting file movement: minimally invasive instrumentation.

INTRODUCTION: Although nickel-titanium (NiTi) rotary instruments may produce a well- tapered root canal with a low tendency of aberrations, these are generally perceived to have a high fracture risk during use and may produce significant forces on root dentin during instrumentation, which may induce a dentinal defect or crack in the apical part of the root. This study compared mathematically the stress generated by the Self-Adjusting File (ReDent-Nova, Ra'anana, Israel) with conventional rotary instruments during the movement of 3 NiTi endodontic file designs in a curved root canal. METHODS: Stresses were calculated using finite element analysis. Three file designs with tip size ISO #20 were used in this study. Finite element models of ProFile #20/.06 (Dentsply Maillefer, Ballaigues, Switzerland) (a constant tapered shaft), ProTaper Universal F1 (Dentsply Maillefer) (a progressively changing taper shaft), and SAF 1.5 mm (a mesh shaft) were activated within a curved root canal model. The stress generations resulting from the simulated shaping movement were evaluated in the apical root dentin area. RESULTS: The SAF induced the lowest von Mises stress concentration and the lowest tensile principal stress component in root dentin. The calculated stress values from ProTaper Universal F1 and ProFile #20/.06 were approximately 8 to 10 times bigger than that of the SAF. CONCLUSIONS: Stress levels during shaping and the susceptibility to apical root cracks after shaping vary with instrument design. The design of the SAF may produce minimal stress concentrations in the apical root dentin during shaping of the curved canal, which may increase the chance of preservation of root dentin integrity with a reduced risk of dentinal defects and apical root cracking.

Flexural stiffness and stresses in nickel-titanium rotary files for various pitch and cross-sectional geometries.

INTRODUCTION: Shape is the main determinant of mechanical performance for nickel-titanium rotary instruments. This study evaluated how pitch and cross-sectional geometry affected flexural stiffness and stresses. METHODS: Finite element models of rotary instruments with 4 cross-sectional geometries (triangle, slender-rectangle, rectangle, square) and 3 pitches (5-, 10-, 15-threads) were created, featuring superelastic nickel-titanium properties. All models had the same length, taper, and external peripheral radius; cross-sectional area and/or center-core area varied. The clamped shaft was rotated axially, while the tip was deflected 5 mm. Flexural stiffness and maximum von Mises stresses were calculated. RESULTS: Stiffness and maximum stress decreased with decreasing pitch (increasing threads). Doubling or tripling the threads for the triangular or rectangular cross sections decreased the stiffness and stress 6% and 12%, respectively; square cross sections were less affected (1% and 3% decrease, respectively). Square cross sections (higher cross-sectional and center-core areas) had higher stiffness and stresses than other models with same deflection. Rectangular and triangular models with the same center-core areas had similar stresses, but the rectangular model was 30%-40% stiffer. The slender-rectangle had the smallest center-core area and the lowest stiffness and stresses. Both rectangular cross sections caused stiffness and stress variations with rotation angle (13% for slender-rectangle); larger pitch caused more variation. CONCLUSIONS: Under the same tip deflection (simulating canal curvature), flexural stiffness and stress correlated with center-core area. Increasing pitch increased flexural stiffness and stresses.

Comparison of torsional stiffness of nickel-titanium rotary files with different geometric characteristics.

INTRODUCTION: The aim of this study was to evaluate the theoretical effect from pitch and cross-sectional geometry on torsional stiffness of nickel-titanium (NiTi) instruments. METHODS: Finite element models of NiTi rotary instruments with different cross-sectional geometries and different number of threads were made for comparison of torsional stiffness. Four cross-sectional shapes were tested: triangle, slender rectangle, rectangle, and square. Taper and external peripheral radius were the same for all models, whereas cross-sectional area and/or center core area were varied. Three pitch values (5, 10, and 15 threads) were tested for each type of cross-sectional geometry. The torsional stiffness of the 12 resulting finite element models was calculated by twisting the file shanks 20 degrees while holding the file tip at apical 4 mm. RESULTS: The file models with larger pitch (fewer threads) had lower torsional stiffness. The models with the rectangular cross section had higher torsional stiffness than models with the triangular cross section, even when the cross-sectional areas were the same or the center core area was smaller. File models with larger cross-sectional area had higher torsional stiffness. CONCLUSIONS: Torsional deformation and/or fracture of NiTi rotary files might be reduced by reducing the pitch (increasing the number of threads) and increasing the cross-sectional areas rather than the center core area.

Correlation between experimental cyclic fatigue resistance and numerical stress analysis for nickel-titanium rotary files.

INTRODUCTION: The aim of this investigation was to study cyclic fatigue resistance of various nickel-titanium (NiTi) rotary files under various root canal curvatures by correlating cyclic fatigue fracture tests with finite-element analysis (FEA). METHODS: Four NiTi rotary instruments with different cross-sectional geometries but comparable sizes were selected for this study: ProTaper (Dentsply Maillefer, Ballaigues, Switzerland), ProFile (Dentsply Maillefer), HeroShaper (Micromega, Besançon, France), and Mtwo (VDW, Munich, Germany). The ProFile and HeroShaper files were of size 30/.06 taper, the Mtwo was of size 30/.05 taper, and the ProTaper was F3. The cyclic fatigue test was conducted in a custom-made device that simulated canals with 25°, 35°, and 45° curvature. For the FEA, the file models were meshed, and 17-mm long curved canals were modeled to have same curvatures as the cyclic fatigue tests. Numerical analysis was performed to determine the stress distributions in the NiTi instruments while they rotated in the simulated curved canals. RESULTS: ProTaper (the stiffest instrument) showed the least cyclic fatigue resistance and highest stress concentration for all tested curvatures, whereas Mtwo showed the best cyclic fatigue resistance. A comparison between the FEA and fatigue results showed that when stresses increased, the number of instrument rotations to fracture decreased. Maximum stresses in the instruments predicted the approximate location of the fatigue fracture. CONCLUSIONS: The stiffer instrument had the highest stress concentration in FEA and the least number of rotations until fracture in the cyclic fatigue test. Increased curvature of the root canal generated higher stresses and shortened the lifetime of NiTi files. Finite-element stress analysis reflected cyclic fatigue fracture resistance.

Potential relationship between design of nickel-titanium rotary instruments and vertical root fracture.

INTRODUCTION: Nickel-titanium (NiTi) rotary files can produce cleanly tapered canal shapes with low tendency of transporting the canal lumen. Because NiTi instruments are generally perceived to have high fracture risk during use, new designs have been marketed to lower fracture risks. However, these design variations may also alter the forces on a root during instrumentation and increase dentinal defects that predispose a root to fracture. This study compared the stress conditions during rotary instrumentation in a curved root for three NiTi file designs. METHODS: Stresses were calculated using finite element (FE) analysis. FE models of ProFile (Dentsply Maillefer, Ballaigues, Switzerland; U-shaped cross-section and constant 6% tapered shaft), ProTaper Universal (Dentsply; convex triangular cross-section with notch and progressive taper shaft), and LightSpeed LSX (Lightspeed Technology, Inc, San Antonio, TX; noncutting round shaft) were rotated within a curved root canal. The stress and strain conditions resulting from the simulated shaping action were evaluated in the apical root dentin. RESULTS: ProTaper Universal induced the highest von Mises stress concentration in the root dentin and had the highest tensile and compressive principal strain components at the external root surface. The calculated stress values from ProTaper Universal, which had the biggest taper shaft, approached the strength properties of dentin. LightSpeed generated the lowest stresses. CONCLUSION: The stiffer file designs generated higher stress concentrations in the apical root dentin during shaping of the curved canal, which raises the risk of dentinal defects that may lead to apical root cracking. Thus, stress levels during shaping and fracture susceptibility after shaping vary with instrument design.

Comparison of forces generated during root canal shaping and residual stresses of three nickel-titanium rotary files by using a three-dimensional finite-element analysis.

The study was aimed to compare the stress distribution during simulated root canal shaping and to estimate the residual stress thereafter for some nickel-titanium rotary instruments. Three brands of instruments (ProFile, ProTaper, and ProTaper Universal; Dentsply Maillefer) were scanned with micro-computed tomography to produce a real-size, 3-dimensional model for each. The stresses on the instrument during simulated shaping of a root canal were analyzed numerically by using a 3-dimensional finite-element package, taking into account the nonlinear mechanical behavior of the nickel-titanium material. From the simulation, the original ProTaper design showed the greatest pull in the apical direction and the highest reaction torque from the root canal wall, whereas ProFile showed the least. In ProTaper, stresses were concentrated at the cutting edge, and the residual stress reached a level close to the critical stress for phase transformation of the material. The residual stress was highest in ProTaper followed by ProTaper Universal and ProFile.