Thermoplastic Sheets Research Articles

Development of the forming limit diagram for fiber-reinforced thermoplastic composites and its temperature effect

The aim of this study is to investigate the formability properties of thermoplastic composite sheets and to develop a forming limit diagram (FLD) for them under ambient and elevated temperatures. Polypropylene thermoplastic composite sheets reinforced with unidirectional continuous glass fibers in a four-layer 0–90 layup were used in this research. Experimental findings demonstrate that the failure of samples at room temperature is more similar to brittle failure and occurs suddenly, whereas at elevated temperatures, the failure resembles ductile failure and occurs gradually. Employing the Nakajima method, a forming limit diagram for the composite material was successfully established at both ambient and elevated temperatures. The resultant forming limit diagrams illustrate an augmented strain tolerance of the material at elevated temperatures. Notably, despite the increased depth of stretch observed at elevated temperatures in comparison to ambient conditions, a concomitant reduction in the force requisite to induce deformation is evident.

A DISTINCTIVE APPROACH TO REHABILITATE PATIENT WITH BILATERAL MAXILLECTOMY DEFECT BY TWO-PIECE HOLLOW OBTURATOR- CASE REPORT

An obturator is a common tool for prosthetic rehabilitation following invasive surgery, particularly in a total maxillectomy case. However, loss of teeth, palatal denture-bearing area, and vestibular retentive undercuts leaves an inadequate anatomic base to construct the definitive prosthesis. This results in compromised retention and stability. The retention problem can be resolved by fabricating an obturator that engages remaining undercuts. But in such acquired large defects, if all undercuts are engaged, the prosthesis may become too heavy, non-retentive, and challenging to insert, particularly in patients with very high and large defects. Therefore, in this case fabrication of two-piece magnet retained hollow obturator was described to make a prosthesis light weight with the use of thermoplastic polyvinyl chloride sheet in first part which provides adequate retention by engaging the desirable undercuts. The second part of the obturator was made hollow by the use of urinary catheter that was removed easily after completion of denture processing. After this, both the parts were attached together with the use of magnets. This technique is economical and easy to use to restore both function and esthetics in patients with bilateral maxillectomy defect.

Influence of one-dimensional material flow on mechanical properties and fiber orientation distribution of thin-ply carbon fiber reinforced thermoplastics sheet molding compounds

The molding flow of carbon fiber reinforced thermoplastic sheet molding compounds (CFRTP-SMC) is complex and requires a comprehensive understanding of underlying processes. This study investigates the material behavior during compression molding processes, focusing on the influence of the ratio of initial material charge area over mold area (charge ratio) on mechanical properties. The results highlight the CFRTP-SMC material's excellent flowability and moldability and confirm that the mechanical properties and internal morphology change with charge ratios. In addition, a correlation between mechanical properties and internal morphology is established through quantitative analysis of fiber orientation distributions using X-ray computed tomography. This comprehensive investigation not only sheds light on the molding ‘behavior of CFRTP-SMCs, but also underscores the importance of material charge ratios in influencing the mechanical properties. This study also provides a case study for validating numerical process models.

Low‐Volume Cores for Fabrication of Compact, Versatile, and Intelligent Soft Systems

AbstractThis study introduces the low‐volume core (LVC) fabrication method, which enables the monolithic molding of compact, complex, versatile, and intelligent soft robotic systems. This method uses thin and flexible thermoplastic sheets to mold internal chambers in soft fluidic actuators, valves, and circuits. The LVC fabrication method creates low‐volume networks in soft actuators (LV‐net actuators) that can be made with compact and complex geometries, enabling both low actuation volume input and multi‐degree‐of‐freedom actuators. LVC fabrication can also be used for compact, completely soft, and monolithic logic components (valves with low‐volume core, also called as LV valves) to provide directional resistance as well as a switching mechanism that enables fluidic logic in soft systems. The compatibility of the fabrication methods for both soft actuators and valves facilitates the creation of compact, integrated, and versatile soft robotic systems with embodied intelligence. This study introduces two examples of such intelligent soft robotic systems that integrate both LV‐net actuators and LV valves to demonstrate capability for complex system fabrication.

Effect of the Height of a 3D-Printed Model on the Force Transmission and Thickness of Thermoformed Orthodontic Aligners.

This research aims to investigate the influence of model height employed in the deep drawing of orthodontic aligner sheets on force transmission and aligner thickness. Forty aligner sheets (Zendura FLX) were thermoformed over four models of varying heights (15, 20, 25, and 30 mm). Normal contact force generated on the facial surface of the upper right central incisor (Tooth 11) was measured using pressure-sensitive films. Aligner thickness around Tooth 11 was measured at five points. A digital caliper and a micro-computed tomography (µ-CT) were employed for thickness measurements. The normal contact force exhibited an uneven distribution across the facial surface of Tooth 11. Model 15 displayed the highest force (88.9 ± 23.2 N), while Model 30 exhibited the lowest (45.7 ± 15.8 N). The force distribution was more favorable for bodily movement with Model 15. Thickness measurements revealed substantial thinning of the aligner after thermoforming. This thinning was most pronounced at the incisal edge (50% of the original thickness) and least at the gingivo-facial part (85%). Additionally, there was a progressive reduction in aligner thickness with increasing model height, which was most significant on the facial tooth surfaces. We conclude that the thermoplastic aligner sheets undergo substantial thinning during the thermoforming process, which becomes more pronounced as the height of the model increases. As a result, there is a decrease in both overall and localized force transmission, which could lead to increased tipping by the aligner and a diminished ability to achieve bodily movement.

Mechanical Properties of Thermoplastic Cassava Starch/Coconut Fibre Composites: Effect of Fibre Size

This research aims to study the thermal and mechanical properties of biodegradable thermoplastic cassava starch (TPCS) reinforced with various sizes of coconut husk fibre (CHF). The range of fibre sizes used was 125, 200, and 300 μm. These CHFs were integrated into a thermoplastic cassava starch matrix to make bio-composites. After integrating all components, the bio-composites were hot-pressed at 155°C for 60 minutes to produce thermoplastic sheets. Tensile and flexural tests were carried out to examine the mechanical characteristics of TPCS/CHF composites. The samples were also characterised using Thermogravimetric Analysis (TGA), X-ray diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), and Scanning Electron Microscopy (SEM). The findings demonstrated that a smaller 125 μm CHF improved the mechanical properties higher than other fibre sizes. Fibre with 300 μm showed more voids, which led to lower material strength. TGA results showed that 300 μm fibres enhanced the crystallinity and thermal stability of the material. FTIR and TGA showed that CHF incorporation increased intermolecular interactions and thermal stability. Overall, a smaller fibre size of 125 μm showed a better reinforcement effect than the larger fibre sizes, which enhanced the materials’ tensile and flexural properties. This study demonstrated that modified TPCS/CHF has shown enhanced functionality than neat TPCS.

Ageing behaviour of folded joints produced by fusion bonding of an outer metal sheet and an inner organic sheet

Adhesive hemming is a process used in the automotive industry to join two metal sheets with good structural performance and good optical appearance of the rim. A new approach is to replace the inner metal sheet by a fibre-reinforced thermoplastic polymer sheet. The joining method used is fusion bonding. This can reduce process time, cost and weight of the finished part. As process route cold hemming is used where the outer metal sheet is first folded around the inner organic sheet at room temperature and afterwards thermally joined by induction. The aim of this work in particular is to investigate the behaviour under accelerated ageing conditions. Especially the cathodic dip coating as corrosion prevention and the air in the fold were varied. The latter can vary in the production process due to manufacturing. In addition, a pre-treatment of the metal surface with a laser was investigated to enhance the mechanical strength of the joint. The samples were produced with a three-step hemming process combined with inductive heating. The applied materials were an organic sheet made of polyamide-6 as matrix material and zinc coated steel. Conditioning according to DIN 1110 and the ageing test VDA 233-102 were applied to laboratory samples. It was shown that conditioning of the specimen reduces the maximal pull out force only slightly while ageing according to VDA 233-102 decreases the pull out force by about 50 %. Furthermore, the air gap has a significant influence on the ageing behaviour of the specimen while the cathodic dip coating only prevents the steel from corrosion but has no influence on the bond strength.

Heat-assisted friction stir incremental sheet forming of thermoplastics

Incremental sheet forming (ISF) has been attracting increasing interests for customised manufacture of thermoplastics, but the application in high-performance and hard-to-form thermoplastics is still a challenge. This paper develops a new heat-assisted friction stir incremental sheet forming (HAFS-ISF) process to form polyether ether ketone (PEEK) and polymethyl methacrylate (PMMA, acrylic). Flexible heating tapes and tool rotational friction heat the thermoplastic sheet on both bottom and top surfaces, which maintain the sheet material at high temperature and reduce the through-thickness temperature gradient. Results are given for the effect of key parameters on forming temperature, force, accuracy and thickness distribution. Spindle speed has the most significant effect on all the studied aspects, followed by the pre-heating temperature, while feed rate and step size have less effect. With lower spindle speed of 100 rpm, the through-thickness temperature gradient is improved. Compared with PEEK parts, more uniform forming temperature and smaller forming force can be observed for PMMA parts. But the material brittleness causes worse formability, and the severer twist and stretching effect affect the forming accuracy of PMMA parts. Forming accuracy, fracture and twist are discussed by developing analytical models. The model for forming accuracy considers the initial bending effect and springback. The fracture is discussed by modelling the stress triaxiality and equivalent strain distribution under contact. While the model for twist considers effect of the applied torque on shear strain energy and continuous accumulation of twist along the tool path. By comparing analytical models and testing observations, the effectiveness of the models is confirmed to understand the underlaying mechanisms and to address a few challenges.

A comparative study on tensile strength of various thermoplastic polymers sheets following thermoforming on a pre-treatment and post-treatment maxillary model of a patient: an in vitro study.

Thermoplastic polymers show alteration in their mechanical properties after thermoforming on a dental model. The purpose of this in-vitro study was to evaluate the tensile strength of different thermoplastic polymer sheets thermoformed on a pre-treatment (moderate crowding) and post-treatment (well-aligned) maxillary model of a patient. Forty maxillary models (Twenty Pre-treatment & twenty Post-treatment of uniform dimension) were made by duplicating them using alginate Hydrogum 5 (Zhermack). Samples were then divided into eight groups of 5 samples each. The thermoplastic sheets Imprelon® (Scheu-Dent), AVAC R® (Jaypee), Placa Crystal® (BioART), EZ-VAC® (3A Medes)-1.0mm thick were thermoformed on these models respectively. The sample was retrieved using ceramic bur mounted on a straight hand-piece and subjected for testing using TINIUS Olsen 10ST micro universal testing machine and recorded. There was no statistically significant difference (P > .05) in tensile strength of thermoformed thermoplastic polymer sheets between pre-treatment and post-treatment maxillary model. Tensile strength of EZ-VAC (3A Medes) showed higher variation between pre-treatment and post-treatment maxillary model though it was found to be statistically insignificant (P > .05). Significant difference (P < .05) was seen between groups when they were compared separately among pre-treatment and post-treatment models. Placa Crystal (BioART) among the pre-treatment group, EZ - VAC (3A Medes) among the post-treatment group, showed highest tensile strength. Results of the study highlights the necessity to test materials in conditions which stands in accordance with the clinical scenario to a considerable extent and also emphasizes the need for further study in aligner.

Preload relaxation behavior and its influence on the mechanical performance of bolted carbon fiber‐reinforced thermoplastic sheet molding compound joints

AbstractIn this study, the relaxation of the initial tightening preload of bolted carbon fiber reinforced thermoplastic sheet molding compound (CFRTP‐SMC) joints was experimentally investigated under different temperatures and initial preload conditions. The influence of preload relaxation on the bolted structures was evaluated using static bearing tests, whereas the failure modes during the test were verified based on metallographic observations. The experimental results indicate that the speed of the preload relaxation can be accelerated by increasing the temperature and initial preload. The static bearing strength of the bolted SMC material decreased with a continuous increase in the preload loss. Furthermore, the existence of a lateral preload protected the material around the assembly hole from buckling, resulting in a higher static bearing strength. The shielding effect of the preload was weakened after the relaxation of the initial preload.Highlights Elevated temperature and initial preload can expedite the relaxation process. Preload loss will result in a declined static bearing performance. Initial tightening preload can protect the bolted SMC material from buckling.

A promising strategy for enhancing fire resistance of steel structure: a composite thermoplastic polyurethane sheet adhered to steel plate

It is an effective passive fire protection method for the steel structure by painting fireproof coatings. Here, a feasible strategy for enhancing the fire resistance of steel structures is proposed. Specifically, a kind of adhesive composite sheet based on thermoplastic polyurethane (TPU), ammonium polyphosphate (APP), polyhedral oligomeric octaphenylsilsesquioxane (OPS), titanium dioxide (TiO2) and sodium silicate was constructed and named as Sheet-Ti/Na. The as-prepared Sheet-Ti/Na exhibited excellent flame retardancy and smoke suppression performance. In addition, the Sheet-Ti/Na can firmly adhere to the steel plate through hot pressing and adhesive bonding methods, acting as a non-traditional fireproof “coating”. This feasible coating method can effectively enhance the fireproof and thermal insulation of the steel plates under the action of the hydrocarbon fire at about 1100 ℃. After testing, the char layer of Sheet-Ti/Na can still firmly adhere to the steel plate without any detachment or cracking. Finally, a ceramic-like reaction among TiO2, APP, OPS and sodium silicate to generate pyrophosphates (TiP2O7 and SiP2O7) was clarified. The thermal insulation, flame retardancy and smoke suppression mechanisms of the Sheet-Ti/Na system also were stated. This work offers a promising strategy for rapidly and efficiently preparing fireproof and thermal insulation “coatings” for steel structures.

Processing Method and Performance Evaluation of Flame-Retardant Corrugated Sandwich Panel.

In this study, in order to expand the engineering application range of thermoplastic corrugated sheets, flame-retardant thermoplastic corrugated sheets were prepared by the thermoplastic molding method. Based on our previous research results, we prepared flame-retardant prepreg tapes with the flame retardant addition accounting for 15%, 20%, and 25% of the resin matrix. Then, we prepared flame-retardant thermoplastic corrugated sandwich panels with corresponding flame retardant addition amounts. The limiting oxygen index test, vertical combustion test, cone calorimetry test, and mechanical property test were carried out on each group of samples and control group samples. The results showed that when the flame retardant was added at 25%, the flame retardant level could reach the V0 level. Compared with the control group, the flexural strength and flexural modulus decreased by 2.6%, 14.1%, and 19.9% and 7.3%, 16.1%, and 21.9%, respectively. When the amount of flame retardant was 15%, 20%, and 25%, respectively, the total heat release decreased by 16.3%, 23.5%, and 34.1%, and the maximum heat release rate decreased by 12.5%, 32.4%, and 37.4%, respectively.

Preparation and properties of semi-alicyclic thermoplastic polyimide sheets from stereoisomeric hydrogenated pyromellitic dianhydrides and fluorinated diamine

Preparation and properties of semi-alicyclic thermoplastic polyimide sheets from stereoisomeric hydrogenated pyromellitic dianhydrides and fluorinated diamine

Thermoforming Simulation of Woven Carbon Fiber Fabric/Polyurethane Composite Materials

A finite element simulation was utilized in this work to analyze the thermoforming process of woven carbon fiber fabric/polyurethane thermoplastic composite sheets. In the simulation that may be classified as a discrete method, the woven carbon fiber fabric was treated as an undulated fill yarn crossed over an undulated warp yarn, and the resin was considered separately. Then, they were combined to represent the composite sheets. To verify this simulation, bias extension tests under three constant temperatures were executed. After that, the composite was thermoformed into a U-shaped structure and small luggage. From the bias extension tests, the finite element simulation and material properties of the fiber and resin were confirmed. From the comparison of the thermoformed products, the present simulation could provide the deformed profile and fiber-included angles and has good agreement with the experiment. The results also indicate that the stacking sequences of [(0°/90°)]4 and [(+45°/−45°)]4 have quite different product profiles and fiber-included angles.

Simplified Appliance for Lip Biting Habit—A Case Report

Lip biting habit can cause severe malocclusions and should be intercepted early in age. The lip bumper device is a helpful treatment as it can stop the habit and prevent the resulting malocclusion. Lip biting habit is intercepted by removable or fixed lip bumper. A simplified appliance for lip biting habit that is easy to fabricate and is more accepted and comfortable for the patient was designed. It consists of a thermoplastic sheet with a labial acrylic pad as in a conventional lip bumper appliance. Improved patient compliance was noted with added advantage of ability to maintain better oral hygiene.

Influence of Processing Conditions on the Generation of Surface Defects in a Heat-and-Cool Hybrid Injection Molding Technique for Carbon Fiber-Reinforced Thermoplastic Sheets and Development of a Suitable Mold Heated by Far-Infrared Radiation.

Recently, hybrid injection molding-a type of overmolding technology in which a short carbon fiber-reinforced thermoplastic is injection molded over a compression-molded carbon fiber-reinforced thermoplastic (CFRTP) sheet-has been introduced. A heat-and-cool hybrid injection molding technique has also been introduced for practical use. The technique yields high-quality molded products. This is achieved through the heating of the mold cavity surface to a temperature higher than the melting point of the base polymer impregnated into the carbon fiber fabric. However, few experimental analyses of the molding phenomena in heat-and-cool hybrid injection molding have been reported. In particular, the effect of the processing conditions on the transfer of the mold cavity surface shape to the CFRTP sheet has not been clarified in detail. Therefore, it has been impossible to take extensive measures when defects are generated in molded products. In this study, a mold is designed and fabricated for use with far-infrared radiation heating, a variotherm technology that is suitable for the experimental analysis of the heat-and-cool hybrid injection molding phenomenon. In particular, a mold is designed and fabricated to continuously perform the following three processes using only an injection molding machine: (1) the radiation heating of both the CFRTP sheet and the mold cavity surface using a far-infrared radiation heater, (2) the compression molding of the CFRTP sheet, and (3) the injection molding of the melt. The effects of the heating conditions of the mold and the injection molding process conditions on the appearance characteristics of the molded products are clarified using this mold and a far-infrared radiation heater.

Heated press welding: analysis of the parameters influencing the mechanical strength of hybrid PA66/PA12 thermoplastic and S235 steel sheet joints

ABSTRACT This study aims to optimize and characterize hot pressed polyamide/steel hybrid joints as a potential solution for reducing energy costs in public transport through structural lightweighting. The mechanical performance of these joints is compared to traditional bonding methods, specifically investigating two types of joints: PA66/steel and PA12/steel. A design of experiments approach is employed to explore the influence of process parameters, with a particular focus on the cooling rate and heating temperature as key factors. By determining the optimal process parameters, the study emphasizes the importance of reaching the polymer pyrolysis point and achieving the fastest cooling rate to achieve optimal results. The findings reveal that these hybrid joints exhibit comparable average shear strength values to bonded joints, showcasing their potential as effective joining methods. In conclusion, future developments in hybrid polymer/metal joining processes utilizing thermal methods should prioritize rapid and uniform heating at the polymer/metal interface to initiate pyrolysis selectively at the polymer surface for bond formation. Subsequent rapid cooling is essential to cease pyrolysis and prevent polymer degradation within its volume. These insights are crucial for successful implementation of such processes in various industrial applications.

Wearable Electrospun Piezoelectric Mats Based on a PVDF Nanofiber-ZnO@ZnS Core-Shell Nanoparticles Composite for Power Generation.

This work adopted a strategy to use new functional high-performance piezoelectric materials for sustainable energy production in wearable self-powered electrical devices. An innovative modification in electrospinning was used to produce highly aligned nanofibers. In the nanogenerator, the flexible membrane constituents were tunefully combined. The novel composite nanofibers were made of Poly (vinylidene fluoride) PVDF, loaded with ZnO@ZnS core-shell nanoparticles to achieve a non-brittle performance of the hetero nanoparticles and piezoelectric polymer. A nanofiber mat was inserted between two thermoplastic sheets with conductive electrodes for application in wearable electronic devices. Complete spectroscopic analyses were performed to characterize the nanofiber's material composition. It is shown that the addition of 10 wt % ZnO@ZnS core-shell nanoparticles significantly improved the piezoelectric properties of the nanofibers and simultaneously kept them flexible due to the exceedingly resilient nature of the composite. The superior performance of the piezoelectric parameter of the nanofibrous mats was due to the crystallinity (polar β phase) and surface topography of the mat. The conversion sensitivity of the PVDF device recorded almost 0.091 V/N·mm3, while that of the PVDF-10 wt % ZnO@ZnS composite mat recorded a sensitivity of 0.153 V/N·mm3, which is higher than many flexible nano-generators. These nanogenerators provide a simple, efficient, and cost-effective solution to microelectronic wearable devices.

Development and Characterization of Sugar Palm (Arenga Pinnata (Wurmb. Merr)) Fiber Reinforced Cassava (Manihot esculenta) Starch Biopolymer Composites

ABSTRACT The study aims to develop a biopolymer composite made of sugar palm fiber and cassava starch that may degrade over time and to investigate the physical and structural characteristics of biocomposite films. Sugar palm fiber (SPF) was cast into a biocomposite with cassava starch (CS) as the matrix and fructose as the plasticizer using the casting process. The thermoplastic CS composite sheet was loaded with different amounts of SPF (0%, 5%, 10%, 15%, and 20% dry starch). The addition of SPF considerably improved the physical and thermal properties. It enhanced the thickness of the material while lowering its density, water content, and biodegradability. However, there was no significant increase in the tensile properties of the composite films. The filler had been absorbed into the matrix, according to SEM micrographs. With a higher concentration of SPF, the SPF/CS films had a more heterogeneous surface. It is indeed possible that the addition of SPF changed the film characteristics of cassava starch, potentially compromising the performance of the films. Overall, the findings of this study concentrate on enlightening about biopolymer composite film and highlighting its great potential for the food packaging market.

Investigation of Metal Wire Mesh as Support Material for Dieless Forming of Woven Reinforcement Textiles

Within the rapidly growing market for fiber-reinforced plastics (FRPs), conventional production processes involving molds are not cost-efficient for prototype and small series production. Therefore, new flexible forming techniques are increasingly being researched, many of which have been inspired by incremental sheet metal forming (ISF). Due to the different deformation mechanisms of woven reinforcement fibers and metal sheets, ISF is not directly applicable to FRP. Instead, shear and bending of the fibers need to be realized. Therefore, a new dieless forming process for the production of FRP supported by metal wire mesh as an auxiliary material is proposed. Two standard tools, such as hemispherical punches, are used to locally bend a reversible layup of metal wire mesh and woven reinforcement fiber fabric enclosed in a vacuum bag. Therefore, the mesh aids in introducing shear into the material due to its ability to transmit compressive in-plane forces, and it ensures that the otherwise flexible fabric maintains the intended deformation until the part is cured or solidified. Basic experiments are conducted using thermoset prepreg, woven commingled yarn fabric, and thermoplastic organo sheets, proving the feasibility of the approach.