Polyamide Specimens Research Articles

On the difference in material structure and fatigue properties of polyamide specimens produced by fused filament fabrication and selective laser sintering

The present paper describes the influence of both flexure quasi-static and fatigue loading on polyamide 12 (PA12) specimens fabricated by fused filament fabrication (FFF) and selective laser sintering (SLS) processes. Rectangular prisms (ISO 178:2010) of polymer were printed and tested under sinusoidal three-point bending fatigue loading at a frequency of 5 Hz. The differences in porosity, surface roughness, and degree of crystallinity are systematically measured and linked to the mechanical fatigue properties. Fatigue analysis in the visco-elastic domain of the polymer is fully described, from fatigue behavior to energy analysis. Here, we have shown that the fatigue properties of the FFF specimens are found to be higher than those of the SLS specimens, despite their lower degree of crystallinity (more than four times). The presence of pores and their growth during fatigue tests in the sintered PA12 specimen seem to be responsible. The fatigue loss factor analysis shows that at lower stress levels, PA12 material reveals its characteristic slight visco-elastic dissipation and heating as its lifetime was exhausted. Also, the obtained results of additively manufactured PA12 were compared with those of materials obtained by injection molding (IM) and extrusion techniques. The quasi-static flexural properties of PA12 obtained by FFF and SLS processes reveal better characteristics compared to IM and extruded specimens. However, the fatigue properties of the SLS-processed polymer are 24% and 40% less than those of materials obtained by IM and extrusion.

Transmission Laser Welding of Polyamides: Effect of Process Parameter and Material Properties on the Weld Strength

Transmission laser welding (TLW) is an environmentally friendly and versatile process for assembling polymeric parts. Welding by transmission requires the upper element to be transparent to the laser wavelength whereas the inferior part is absorbent to the same wavelength. Thus, the energy of the laser beam is concentrated at the interface, allowing both polymeric parts to be melted. Upon temperature, the interdiffusion of polymeric chains takes place at the interface, creating bridges between both parts, resulting in a strong assembly. Laser welding is in principle applicable to any thermoplastic, provided that it is transparent to the laser wavelength.In the present work, carbon black filled polyamide has been assembled with two types of 2 mm and 4 mm thick partially transparent polyamide specimens. The effect of the process parameters such as energy density, speed of the laser beam and the part thickness have been correlated with the mechanical strength of welds, measured by wedge tests. The thermomechanical and optical properties of the samples have been assessed and correlated to the dimensions of the heat affected zone (HAZ). For a deeper understanding of the effect of optical and thermal properties of the materials on the quality of the welded joint, a numerical modeling is proposed. The ray tracing method is able to determine the light scattering and the absorption at the micro-scale in the polyamide semi-transparent part. The results of the ray tracing are the volume term source and the heat flux that generates temperature elevation.

Bond strength of different wood-plastic hybrid components prepared through back injection moulding

Golf tees with a plastic head and wooden shaft were prepared by back injection moulding of a beech wood (Fagus sylvatica) shaft with different polymers (i.e. ionomer, polypropylene, and polyamide). In order to facilitate adhesion between the polymer melt and the wood surface, the wooden shafts were pre-treated with different primer substances, including a commercially available primer for ABS edges, a 10% solution of alkyl ketene dimer (AKD) in toluene and tumbling lacquer. The mechanical strength of the wood-plastic interphase was characterized by applying a pull-out test. Bond strength values of more than 9 N/mm² were observed for polyamide, whereas ionomer and polypropylene specimens achieved values between 0.7 and 3.8 N/mm². Surprisingly, the used primers failed to improve interfacial adhesion with the exception of the ionomer sample pre-treated with the commercial ABS-primer. Although light microscopy and SEM revealed some differences in the penetration behaviour of the different polymers as well as in the extent of plastic wood deformation imposed during injection moulding, the chemical nature of the polymer seems to be the most important determinant for the bond strength of wood-plastic hybrid components.

Build Orientation Influence on some Mechanical Properties of 3D-Printed Polyamide Specimens

Additive manufacturing [AM] is a type of production technology characterized by the additive nature of stacking and unifying individual layers, with the main advantage that parts with complex geometries can easily be obtained, compared to conventional production methods. Due to its working principle, i.e. stacking layers, obtained by melting and solidification, the mechanical characteristics of the built part might be influenced by the build orientation chosen for the specific part. The mechanical behavior, cyclic deformation and fatigue behaviors of additively manufactured metallic parts as compared to their counterparts obtained by conventional processing technologies was reported to be highly dependent on the build orientation. The aim of this study was to assess whether the build orientation will have an impact on the mechanical properties of parts built by Selective Laser Sintering, using polyamide powder as raw material. Samples were built at various inclination degrees, and were further tested in terms of bending, compressive, impact and hardness tests. It was observed that the build orientation has a significant effect on the mechanical properties of parts additively manufactured from polyamide, compared to the behavior presented on the technical sheet of the material, provided by the manufacturer. Keywords: additive manufacturing, mechanical properties, build orientation, Selective Laser Sintering

Moisture transport in PA6 and its influence on the mechanical properties

Various studies have reported the changes in the mechanical properties and the modification in morphology of polyamide due to the absorption of water. However, the relation between the local water content and the alteration in the properties has not been consolidated in a coupled model yet. In the current work, a simulation model is proposed that can capture the diffusion of water as well as simulate the effect of the local moisture content on the stiffness of polyamide (PA6). To this end, a finite element model was developed by coupling of a nonlinear diffusion model and a viscoelastic material model. The Galerkin finite element method was used to formulate the weak form of the equations for the two physical processes. The coupled nonlinear equations were solved with the help of the Newton method. The diffusion process was studied experimentally with the help of gravimetric measurements. Relaxation tests were conducted on the polyamide specimens that were saturated under different moisture levels. Based on these experimental results, the dependency of the material parameters on the local moisture content was identified and an efficient and stable numerical simulation model has been developed.

Impact behavior and fractography of additively manufactured polymers: Laser sintering, multijet fusion, and hot lithography

To reduce the lead time, polymer fuel tanks could be toollessly produced using additive manufacturing (AM) technologies. Detailed knowledge of the performance of AM polymers is essential for the design and development of such components. In instrumented static (0.01 mm/s) and dynamic (2.5 m/s) three-point bending and puncture tests, the impact behaviors of polyamide and methacrylate-based photopolymer test specimens were compared. The polyamide test specimens were produced by laser sintering and multijet fusion, and the photopolymer test specimens were produced by a hot lithography process. Fractography was performed using stereo light and scanning electron microscopy to investigate the fracture surface morphology. The test results were used to analyze the relationships among the surface roughness, shear modulus, and glass transition temperature. The AM polymers revealed comparable force–displacement behaviors in a static three-point bending test, but their impact behaviors differed greatly. The obtained results highlight that the impact performance of AM polymers is an essential design variable for fluid-containing parts.

The macroscopic behavior of pantographic sheets depends mainly on their microstructure: experimental evidence and qualitative analysis of damage in metallic specimens

Recently the exotic properties of pantographic metamaterials have been investigated, and various mathematical models (both discrete and continuous) have been introduced. However, the experimental evidence available up to now concerns only polyamide specimens. In this paper, we use specimens printed using metallic powder. We prove experimentally that the main qualitative and quantitative features of pantographic sheets in planar deformation are independent of the constituting materials, at least when they can be regarded as homogeneous and isotropic at micro-level. Of course, the absolute value of Young’s modulus of constituent material affects the overall reaction force needed to the hard device to impose a given displacement: A first investigation on this effect is also attempted.

Bacterial Colonization and Tissue Compatibility of Denture Base Resins.

Currently, there is minimal clinical data regarding biofilm composition on the surface of denture bases and the clinical tissue compatibility. Therefore, the aim of this experimental study was to compare the bacterial colonization and the tissue compatibility of a hypoallergenic polyamide with a frequently used PMMA resin tested intraorally in a randomized split-mouth design. Test specimens made of polyamide (n = 10) and PMMA (n = 10) were attached over a molar band appliance in oral cavity of 10 subjects. A cytological smear test was done from palatal mucosa at baseline and after four weeks. The monolayers were inspected for micronuclei. After four weeks in situ, the appliance was removed. The test specimens were immediately cultivated on non-selective and selective nutrient media. All growing colonies were identified using VITEK-MS. The anonymized results were analyzed descriptively. A total of 110 different bacterial species could be isolated, including putative pathogens. An average of 17.8 different bacterial species grew on the PMMA specimens, and 17.3 on the polyamide specimens. The highest number of different bacterial species was n = 24, found on a PMMA specimen. On the two specimens, a similar bacterial distribution was observed. Micronuclei, as a marker for genotoxic potential of dental materials, were not detected. This study indicates that the composition of bacterial biofilm developed on these resins after four weeks is not influenced by the type of resin itself. The two materials showed no cytological differences. This investigation suggests that polyamide and PMMA are suitable for clinical use as denture base material.

Z-pin insertion process for through-thickness reinforced thermoplastic composites

This paper presents a novel method for the ultrasonically assisted insertion of metallic z-pins into thermoplastic composites. Mechanical and microstructural investigations were carried out on glass fiber-reinforced polyamide and polypropylene specimens. The insertion of steel pins into thermoplastic composites led to microstructural changes that differ significantly from the known microstructure of z-pinned thermoset fiber-reinforced plastics. Optical microscopy showed an absence of notable fiber waviness and resin-rich zones around each pin. Instead, the fibers were predominantly deflected in the through-thickness direction by the high insertion forces arising during pin penetration. To gain an initial insight on the resulting properties of the z-pin/thermoplastic interface, the mechanical properties of z-pinned thermoplastic composites under mode I loading were investigated using pullout tests. For reference, the pullout behavior of thermoset carbon fiber-reinforced plastic specimens, reinforced with steel pins was determined too. Due to the poor bonding and lack of friction between the pin and laminate, the determined traction loads of the thermoplastic specimens are well below typical values achieved from pin pullout in thermoset laminates.

Double-Layer Surface Modification of Polyamide Denture Base Material by Functionalized Sol-Gel Based Silica for Adhesion Improvement.

Limited surface treatments have been proposed to improve the bond strength between autopolymerizing resin and polyamide denture base materials. Still, the bond strength of autopolymerizing resins to nylon polymer is not strong enough to repair the fractured denture effectively. This study aimed to introduce a novel method to improve the adhesion of autopolymerizing resin to polyamide polymer by a double layer deposition of sol-gel silica and N-2-(aminoethyl)-3-aminopropyltrimethoxysilane (AE-APTMS). The silica sol was synthesized by acid-catalyzed hydrolysis of tetraethylorthosilicate (TEOS) as silica precursors. Polyamide specimens were dipped in TEOS-derived sol (TS group, n = 28), and exposed to ultraviolet (UV) light under O2 flow for 30 minutes. UV-treated specimens were immersed in AE-APTMS solution and left for 24 hours at room temperature. The other specimens were either immersed in AE-APTMS solution (AP group, n = 28) or left untreated (NT group, n = 28). Surface characterization was investigated by fourier transform infrared spectroscopy (FTIR) and atomic force microscopy (AFM). Two autopolymerizing resins (subgroups G and T, n = 14) were bonded to the specimens, thermocycled, and then tested for shear bond strength with a universal testing machine. Data were analyzed with one-way ANOVA followed by Tukey's HSD (α = 0.05). FTIR spectra of treated surfaces confirmed the chemical modification and appearance of functional groups on the polymer. One-way ANOVA revealed significant differences in shear bond strength among the study groups. Tukey's HSD showed that TST and TSG groups had significantly higher shear bond strength than control groups (p = 0.001 and p < 0.001, respectively). Moreover, bond strength values of APT were statistically significant compared to controls (p = 0.017). Amino functionalized TEOS-derived silica coating is a simple and cost-effective method for improving the bond strength between the autopolymerizing resin and polyamide denture base. Amino-functionalized silica coating could represent a more applicable and convenient option for improving the repair strength of autopolymerizing resin to polyamide polymer.

Reverse time migration: introducing a new imaging technique for ultrasonic measurements in civil engineering

ABSTRACTUltrasonic echo testing is widely used in non‐destructive testing in civil engineering to investigate concrete structures, to measure thickness, and to locate and characterise built‐in components or inhomogeneities. Currently, synthetic aperture focusing techniques are mostly used for imaging. These algorithms are highly developed but have some limitations. For example, it is not possible to image the lower boundary of built‐in components like tendon ducts or vertical reflectors. We adopted reverse time migration for non‐destructive testing in civil engineering in order to improve the imaging of complicated structures in concrete. By using the entire wavefield, including waves reflected more than once, there are fewer limitations compared to synthetic aperture focusing technique algorithms. As a drawback, the required computation is significantly higher than that for the techniques currently used.Simulations for polyamide and concrete structures showed the potential for non‐destructive testing. The simulations were followed by experiments at a polyamide specimen. Here, having acquired almost noise‐free measurement data to test the algorithm, we were able to determine the shape and size of boreholes with sufficient accuracy. After these successful tests, we performed experiments at a reinforced concrete foundation slab. We obtained information from the data by reverse time migration, which was not accessible by traditional imaging. The imaging of the location and structure of the lower boundary of the concrete foundation slab was improved. Furthermore, vertical reflectors inside the slab were imaged clearly, and more flaws were found. It has been shown that reverse time migration is a step forward in ultrasonic testing in civil engineering.

Spallation occurrence from polyamide materials irradiated by thermal plasma with water absorption

This paper first describes the effect of water absorption in polyamide material irradiated by thermal plasmas on the occurrence of spallation phenomena. The interaction between polyamide materials and arc plasmas occurs particularly in the low voltage circuit breaker and aerospace fields. Spallation phenomena are those in which polymer particles are ejected from polymer bulk materials irradiated by high heat flux. To confirm the effect of water absorption into the polyamide material on spallation phenomena, polyamide specimens with and without water absorption were irradiated by Ar inductively coupled thermal plasma. The results show that the polyamide specimen with water absorption ejected spallation particles, whereas the polyamide specimen without water absorption were only slightly ejected, indicating that water absorption promotes the occurrence of spallation. The cooling effects of the spallation polyamide 66 (PA66) particles ablation were also estimated in hot air to assess the arc quenching ability from the spallation particle inclusion. This estimation showed that 10 and more PA66 particles inclusion might decrease the air temperature by 3000 K effectively, which can be useful to enhance arc quenching in circuit breakers working in air.

Recycling of PA-12 in Additive Manufacturing and the Improvement of its Mechanical Properties

This study explores possible ways to make Additive Manufacturing (AM) a cradle-to-cradle process, that is, use the leftover from one process as the raw material for another process. The main goal of this study is to develop a set of new polymeric blends with innovative properties, suitable for using in 3-D printing of prosthetic limbs using Fused Deposition Modeling (FDM) technology. Sustainable acting is achieved by reusing polymeric material left over from Selective Laser Sintering (SLS) processes for making raw material for FDM processes. Test specimens of polyamide 12 (PA-12) in its virgin form and used- , un-sintered form alongside specimens of used PA blended with TPU, aramid, or graphite, were produced in a micro-injection moulding machine and then tested for their mechanical properties. This paper provides information about the differences in mechanical characteristics of these different material blends. An unexpected but positive finding was that the differences between virgin and recycled PA-12 are insignificant. The aforementioned additives influenced PA-12 by producing specimens that responded with predictable characteristics which is a significant accomplishment as it lays the groundwork for the next stages of the project.

Effect of Laser Power on Component Strength in Laser Sintering

Prototyping or model making is one of the important steps to finalize a product design. It helps in conceptualization of a design. Before the start of full production a prototype is usually fabricated and tested. RP processes namely Stereo-lithography (SL), Selective Laser Sintering (SLS), Fused Deposition Modeling (FDM) and Laminated Object Manufacturing (LOM) are described. In Selective Laser Sintering (SLS) process, fine polymeric powder like polystyrene, polycarbonate or polyamide etc. (20 to 100 micrometer diameter) is spread on the substrate using a roller. Before starting CO2 laser scanning for sintering of a slice the temperature of the entire bed is raised just below its melting point by infrared heating in order to minimize thermal distortion (curling) and facilitate fusion to the previous layer. The laser is modulated in such a way that only those grains, which are in direct contact with the beam, are affected. Once laser scanning cures a slice, bed is lowered and powder feed chamber is raised so that a covering of powder can be spread evenly over the build area by counter rotating roller. In this process support structures are not required as the un-sintered powder remains at the places of support structure. It is cleaned away and can be recycled once the model is complete. This research has examined the effect of Laser power as well as processing parameters on the mechanical properties of selective laser sintered parts from DURAFORM PA In this research tensile specimens of Polyamide (DURAFORM PA) material as per the test standard ‘ASTM D638’ are fabricated. This test method covers the determination of the tensile properties of unreinforced and reinforced plastics in the form of standard dumbbell-shaped test specimens when tested under defined conditions of pre-treatment, temperature, humidity, and testing machine speed. The effects of varying the Laser power, generated by the laser, on the physical and mechanical properties of produced specimens. The energy density is varied by changing the laser power at a fixed value of laser scan spacing. Knowing the relationship between SLS parameter settings and material properties will make it possible to manufacture parts with predetermined properties, customized for various applications.

Comparison of Three Different Methods for Pile Integrity Testing on a Cylindrical Homogeneous Polyamide Specimen

Three different methods for pile integrity testing are proposed to compare on a cylindrical homogeneous polyamide specimen. The methods are low strain pile integrity testing, multichannel pile integrity testing and testing with a shaker system. Since the low strain pile integrity testing is well-established and standardized method, the results from it are used as a reference for other two methods.

Effect of surface treatment methods on the shear bond strength of auto-polymerized resin to thermoplastic denture base polymer.

PURPOSEPolyamide polymers do not provide sufficient bond strength to auto-polymerized resins for repairing fractured denture or replacing dislodged denture teeth. Limited treatment methods have been developed to improve the bond strength between auto-polymerized reline resins and polyamide denture base materials. The objective of the present study was to evaluate the effect of surface modification by acetic acid on surface characteristics and bond strength of reline resin to polyamide denture base.MATERIALS AND METHODS84 polyamide specimens were divided into three surface treatment groups (n=28): control (N), silica-coated (S), and acid-treated (A). Two different auto-polymerized reline resins GC and Triplex resins were bonded to the samples (subgroups T and G, respectively, n=14). The specimens were subjected to shear bond strength test after they were stored in distilled water for 1 week and thermo-cycled for 5000 cycles. Data were analyzed with independent t-test, two-way analysis of variance (ANOVA), and Tukey's post hoc multiple comparison test (α=.05).RESULTSThe bond strength values of A and S were significantly higher than those of N (P<.001 for both). However, statistically significant difference was not observed between group A and group S. According to the independent Student's t-test, the shear bond strength values of AT were significantly higher than those of AG (P<.001).CONCLUSIONThe surface treatment of polyamide denture base materials with acetic acid may be an efficient and cost-effective method for increasing the shear bond strength to auto-polymerized reline resin.

Fatigue mechanisms description in short glass fibre reinforced thermoplastic by microtomographic observations

Short glass fibre reinforced thermoplastics are promising materials for weight reduction of structures thanks to its very good specific mechanical properties. The current challenge is to provide experimental data concerning damage mechanisms and their kinetics in order to enhance micromechanical models for these materials with complex behaviour. The objective of this work is therefore to observe and explain damage mechanisms regarding spatial configuration of the microstructure. Fatigue tests have been running on reinforced polyamide specimens and interrupted at different levels of the estimated life. 3D pictures of the gage length of these specimens have been obtained by microtomography with high resolution (0.65 µm). This data presents damage location at different stages of lifetime. Thus, debonding, matrix damage and fibre failure have been identified as the three damage mechanisms for these materials. The analysis of the evolution of the damage markers quantity, volume and aspect ratio inform about the kinetic for each mechanism during the material life.

Comparison of Fungal Biofilm Formation on Three Contemporary Denture Base Materials

ABSTRACTStatement of problem: Modern polyamide ‘flexible’ denture base materials have increased in popularity for use in removable partial dentures in the last several years. The introduction of these newer products warrants investigation of their relative potential to develop fungal biofilms.PurposeThe purpose of this study was to investigate the potential of three denture base materials to support fungal biofilm formation.Materials and methodsSpecimens of two ‘flexible’ nylon type materials and one traditional heat processed, methyl methacrylate resin material were studied (both polished and unpolished surfaces). The specimens were coated with saliva and evaluated for fungal (Candida albicans) biofilm formation. The fungal biofilm mass formed on denture substrates were evaluated by dry weight analysis and by determining the number of viable fungal cells in the biofilm by MTT viability assay. Alteration in fungal metabolic function following the treatment of the biofilmC. albicanswith nystatin and fluconazole was determined by XTT assay.ResultsIn general, the unpolished surfaces of the denture disks favored the fungal biofilm, the most being on polyamide specimen, Valplast. Significantly, less biofilm was formed on Duraflex and Lucitone surfaces. Biofim on C. albicans was also found to be resistant to antifungal agents. As compared to freshly incubated (grown) planktonic cells, biofilm fungal cells required significantly higher concentrations of nystatin and fluconazole in order to obtain 50% reduction in metabolic activity.ConclusionThis study demonstrated the differences in denture materials to support fungal biofilm formation, and also difference between polished and unpolished denture material surfaces. The results demonstrated that one of the polyamide materials (duraflex) had lesser potential to biofilm formation than the others.Clinical significanceUnfavorable tissue responses can ensue from the presence of fungal biofilms on dental prosthetics. Resistance to biofilm formation is a factor for dental materials in their selection and usage. This study helps to quantify, evaluate and compare biofilm formation on polished and unpolished surfaces of three commonly used denture base materials. The results of this study helped to identify materials, which may, therefore, be better indicated in clinical applications. Evaluations for the newer denture base materials, specific to these testing methods, appear to be novel in the scientific literature.How to cite this articleJain V, Babu J, Ahuja S, Wicks R, Garcia-Godoy F. Comparison of Fungal Biofilm Formation on Three Contemporary Denture Base Materials. Int J Experiment Dent Sci 2015;4(2):104-108.

Influence of Fiber Orientation and Multiaxiality on the Fatigue Strength of Unnotched Specimens – Lifetime Estimation

In components for the automotive industry, short glass fiber-reinforced thermoplastic parts are increasingly used due to their potential for economical lightweight constructions, for example, by substitution of metal components. In order to guarantee the reliability of these components, fatigue-lifetime assessment concepts for plastic parts under complex service conditions are needed. The multiaxial loading fiber orientations are important factors which affect fatigue life. Therefore, different multiaxiality criteria, together with a new concept capturing the influence of fiber orientation on fatigue strength are proposed in this paper. The fiber orientation is a result of the injection molding process that leads to locally anisotropic behavior, which gives rise to multiaxial stress states. Anisotropic material behavior is modeled by a simulation chain consisting of injection molding simulations, mapping and homogenization and, finally, finite element analysis (FEA). In order to demonstrate the benefit of this simulation chain, results are compared with the isotropic case. Finally, a combined concept including multiaxiality and fiber orientation is presented and applied to fatigue experiments on unnotched specimens of polyamide 6.6 reinforced with 35wt.% short glass fibers.

Experimental Investigation of SLS Process for Flexural Strength Improvement of PA-3200GF Parts

The strength of functional parts is of key importance in additive manufacturing, and the selection of proper parameters is essential to improve manufacturing solutions. Therefore, research is currently focused on determining the influence of process parameters (i.e., part bed temperature, laser power, scan speed, and scan spacing) on the flexural strength of laser-sintered glass-filled polyamide specimens. A response surface methodology-based mathematical model was proposed to predict flexural strength, and the adequacy of the developed model was verified thorough the analysis of variance technique. Further, optimized conditions were established to maximize the output parameter through the desirability function approach.