Polymer Specimens Research Articles

A nature-inspired gradable elliptic-cell lattice structure based on cypress wood texture; theoretical and experimental analysis for mechanical properties

The accessibility and commercialization of additive manufacturing allow scientists to design affordable, light weighted cellular-graded structures with customized mechanical properties. This study introduced a new functionally graded lattice structure inspired by the porous wood texture of cypress. This structure can simultaneously alter the relative density and unit cell shapes by gradual cell size grading and its porosity in each repetition which can provide graded properties along the particular axis and in each structural point. Different mechanical properties and geometrical features are easily achievable by altering the unit cell’s shape and dimensions. Elastic modulus, Poisson’s ratio, and specific energy absorption values depend on ellipses radii in cell scales, layers of lattices, and structures. Porosity and surface-to-volume ratio are calculated with high accuracy for different structures, which can be optimized for biomaterial and bioimplant substitution. Numerical simulation is carried out as two perpendicular uniaxial compressions for extracting the structural properties. In addition, an experimental test on the polymeric specimen, made by the DLP technique, validates the results, which shows good agreement with numerical ones. Designs of experiments were set up to determine the parameters’ main and interaction effects on the mechanical properties. RSM function is evaluated for two radii as factors in three levels in both unit cells and layers. Linear tessellation of a layer and parallel array of two perpendicular sets results in a highly porous, ultra-light, weighted structure.

Ultrasonic welding of printed/molded sustainable polymer specimens with energy directors

Fused deposition modeling is preferred to fabricate the biodegradable poly lactic acid (PLA) parts, owing to its impeccable characteristics, such as, customization, waste minimization and scalability. However, limited printing volume constraint restricts the ubiquitous applications of this technique. The current experimental investigation is focused on the employment of ultrasonic welding technique to address the printing volume challenge. The effect of infill density, type of energy directors (triangular (TED), semicircular (SCED) and cross energy directors (CED)) and different levels of welding parameters have been investigated on the mechanical and thermal behavior of welded joints. Presence of rasters and gap between them plays a pivotal role in overall heat generation at weld interface. The joint performance of 3D printed parts has also been compared with injection molded specimens of same material. All printed/molded welded specimens with CED recorded higher tensile strength than equivalent specimens with TED and SCED. Moreover, These specimens also performed better than specimens without energy directors and recorded higher tensile strength, that is, 317, 73.5, 59.7 and 42% higher for injection molded (IM), 80%, 90% and 100% infill density (IF) specimens without energy directors at lower level of welding parameters (LLWP). These specimens also exhibited higher tensile strength at optimal levels of welding parameters. Although, at medium and higher levels of welding parameters, both printed/molded specimens with CED observed comparatively more degradation of joints due to higher concentration of energy at weld interface. The dynamic mechanical analysis (DMA), thermogravimetric analysis (TGA), derivative thermogravimetry (DTG) and field emission scanning electron microscopy (FESEM) analysis have been performed to substantiate the experimental results.

Mechanical design of a convex-deformable polymer plate

The authors’ previous study introduced a convex-deformable sandwich plate consisting of a pyramid truss core and two face sheets that exhibit a two-dimensional auxetic pattern. Owing to its unique micro-architecture, the sandwich plate successfully underwent adequate convex deformation under bending, even when many chips were embedded in its core. However, the plate was fabricated by adhesively bonding stainless-steel face sheets to a polymer truss core, and this fabrication process was complex and expensive. Moreover, the detailed dimensions of this plate were determined iteratively through trial-and-error. In this study, we develop a fresh approach to monolithically fabricate the entire body of the auxetic plate from a polymer by using three-dimensional printing. First, three mechanical constraints, which are needed for designing the face sheets and the core to realize compliant and convex deformation, unlike that of an ordinary sandwich plate, are defined. A precise mechanical design procedure is applied for dimensional optimization of the plate, and the mechanical behaviors of the fabricated specimen are observed by subjecting it to tensile and bending loads. The optimally designed polymer specimen exhibited a high level of convex deformation, as indicated by its adequate flexural rigidity (D = 0.0565 Nm2) and curvature ratio (0.625) when bent to the minimum curvature radius of ρ = 150 mm.

Elastomeric biodegradable poly(ester amide urethane) as a tough and robust material

Poly(ester amide)s belong to a special class of polymers and their intrinsic properties can be tailored by tuning their chemical structures. In this regard, poly(ester amide urethane) resins were synthesized to circumvent the shortcomings as well as to impart new features into the poly(ester amide) framework. In the present work, various compositions of poly(ester amide urethane) were prepared by varying the proportions of isophorone diisocyanate. The structural analysis of the synthesized polymeric material was accomplished using various techniques viz., FTIR, XPS, PXRD, etc. On investigating the mechanical profile study, it was noted that the polymeric specimens exhibited excellent elongation at break values ranging from 640.81 % to 1875.91 %, thereby rendering traits of a sturdy elastomeric material. The samples also demonstrated outstanding toughness values from 1125.11 MJm−3 to 1895.62 MJm−3. In turn, the polymeric material displayed satisfactory thermal stability above 200 °C along with good chemical resistance values. Disparate aging tests were conducted to assess the durability of the material under stringent environmental conditions. The materials demonstrated remarkable enhancement in tensile strength parameters upon exposure to various aging regimes (heat, UV, etc.) which further promote their utility as robust materials for outdoor applications. Additionally, they revealed exceptionally good biodegradable attributes along with significant cytocompatibility behavior.

Investigation on the fracture behavior of octet-truss lattice based on the experiments and numerical simulations

Octet-truss lattice is an excellent carrier for structure–function integration because of its natural porous characteristics and remarkable bearing capacity. Currently, a significant discussion in its engineering applications revolves around assessing the fracture toughness of the lattice structure. In this paper, the single edge notched bend (SENB) specimens composed of PolyMaxTMPLA with shallow crack are prepared using the Fused Deposition Modelling (FDM) method, and three-point bending tests are conducted to investigate the fracture behavior of the octet-truss lattices. Based on the elastic–plastic fracture behavior of the specimens, the J-integral method is used to calculated the effective fracture toughness and the effect of shallow crack on the fracture toughness was considered. The experimental results show that the effective fracture toughness of the polymer specimens increases linearly with the relative density and the square root of truss length. To study the fracture behavior of lattice structure deeply, the numerical simulations are performed to further analyze the fracture behavior of the structures and verified by the experimental results. The results suggest that the fracture at the nodes and the truss near the nodes is the main failure mode of the specimens. Specially, the truss in the X-Z plane always breaks before the X-Y plane, while the deformation of truss in the Y-Z plane is always elastic. A prediction formula of the effective fracture toughness of 3D printed PLA polymer octet-truss lattice is determined based on a non-dimensional parameter sensitive to the loading mode.

Wear Effect on the Contact between a Metallic Pin and a Rotating Polymeric Specimen

Debris formation is a crucial aspect that determines the lifespan of prosthetic joints. The wearing contact between ultra-high molecular weight polyethylene (UHMWPE) and a Ti alloy surface has been studied in the literature. However, when measuring mass loss, potential errors can arise due to the very small values involved (on the order of some units of 0.1 mg in experiments lasting several hours) and be caused by the absorption of humidity in the specimen, in addition to the lack of accuracy typical of weight scales. These errors can hardly be avoided, but accurate cleaning and drying processes can minimize them. With these premises, the present work aims to determine, by pin-on-disc test, the wear effect in the UHMWPE rotating sheet and Ti6Al4V pin produced by Electron Beam Melting (EBM) under dry and lubricated conditions. The morphology of the worn surface was documented by optical microscopy, and the volume loss of both the rotating specimens and the pin was accurately calculated through the detection of the wear track observed by optical microscopy. In particular, the present work proposes a method for directly determining the volume loss of the polymer to compare it with that obtained with the weight measurement. For both procedures, the uncertainty in evaluating the specific wear rate was analyzed, demonstrating that volume measurement allows for avoiding any possible error associated with weighing the polymeric specimens.

Influences of abrasive particles on tribological behaviours of rotary vane steering gear seals under oil

The wear particles often cause the abnormal wear processes to the rotary vane seals, which lead to seals failure and dropping hydraulic oil pressure, and eventually result in losing of the function of rotary vane steering gear. Clarifying the friction and wear mechanisms between the vane seals and the cylinders and extracting their key wear characteristics are the keys to extend the service life and realize intelligent fault diagnosis of the rotary vane steering gears. Different kinds of hydraulic oils mixed up with different sizes of iron particles were chosen to investigate the abrasive particles on the wear behaviours between the polyurethane polymer and carbon steel specimens. The wear characteristics such as coefficients of friction (COF), wear morphologies, frictional-induced vibration signals were examined and analyzed synthetically. The results showed that the coefficients of friction, wear morphologies, surface roughnesses and vibration signals increased as a function of the iron particle sizes, which indicated that the wear state was gradually worsening. The three-body friction and wear mechanisms were disclosed clearly. There was a certain mapping relationship between the wear characteristics and wear states, and sensing the tribological information between the rubbing pairs, including coefficient of friction, abrasive particle size in hydraulic oil, wear morphology, vibration signal and other characteristics, was a potential and effective way for evaluating or predicting the wear states or failure modes of rotary vane steering gear seals. This study provides a theoretical basis for revealing the friction and wear mechanisms of ship rotary vane steering gear seals, and is useful for accomplishing their intelligent monitoring and fault diagnosis.

Transmission electron microscopy of thick polymer and biological specimens

We explore the properties of elastic and inelastic scattering in a thick organic specimen, together with the mechanisms that provide contrast in a transmission electron microscope (TEM) and scanning-transmission electron microscope (STEM). Experimental data recorded from amorphous carbon are used to predict the bright-field image intensity, mass-thickness contrast and dose-limited resolution as a function of thickness, objective-aperture size, and primary-electron energy E0. Combining this information with estimates of chromatic aberration, objective-aperture diffraction and beam broadening in the specimen, we calculate the achievable TEM and STEM resolution to be around 4 nm at E0 = 300 keV (or below 3 nm at MeV energies) for a 10 µm-diameter objective aperture and 1 – 2 µm thickness of hydrated biological tissue. The 3 MeV resolution for a 10-μm tissue sample is probably closer to 10 nm. We also comment on the error involved in quadrature addition of resolution factors, when one or more of the point-spread functions are non-Gaussian.

Experimental and Numerical Study of the Effect of the Presence of a Geometric Discontinuity of Variable Shape on the Tensile Strength of an Epoxy Polymer

Abstract The presence of geometric discontinuity in a material reduces considerably its resistance to mechanical stresses, therefore reducing the service life of materials. The analysis of structural behaviour in the presence of geometric discontinuities is important to ensure the proper use, especially if it is regarding a material of weak mechanical properties such as a polymer. The objective of the present work is to analyse the effect of the notch presence of variable geometric shapes on the tensile strength of epoxy-type polymer specimens. A series of tensile tests were carried out on standardised specimens, taking into account the presence or absence of a notch. Each series of tests contains five specimens. Two notch shapes were considered: circular (hole) and elliptical. The experimental results in terms of stress–strain clearly show that the presence of notches reduces considerably the resistance of the material, where the maximum stress for the undamaged specimen was 41.22 MPa and the lowest stress for the elliptical-notched specimen was 11.21 MPa. A numerical analysis by the extended finite element method (XFEM) was undertaken on the same geometric models; in addition, the results in stress–strain form were validated with the experimental results. A remarkable improvement was obtained (generally an error within 0.06%) for strain, maximum stress, Young’s modulus and elongation values. An exponential decrease was noted in the stress, strain, and Young’s modulus in the presence of a notch in the material.

Experimental and Numerical Investigation on the Influence Factors of Damage Interference of Patch-Repaired CFRP Laminates under Double Impacts

The impact responses of a patch-repaired carbon-fiber-reinforced polymer (CFRP) specimen under double impacts were compared to study the damage interference mechanism through the combination of experiment and numerical analysis. A three-dimensional finite element model (FEM) with iterative loading based on continuous damage mechanics (CDM) and a cohesive zone model (CZM) was employed to simulate the double-impacts testing with an improved movable fixture at an impact distance of 0 mm-50 mm. The influence of impact distance and impact energy on the damage interference was explored by mechanical curves and delamination damage diagrams of the repaired laminates. When impactors fell within the range of the patch with an impact distance of 0 mm-25 mm at a low level of impact energy, delamination damage of the parent plate caused by the two impacts overlapped, resulting in damage interference. With the continuing increase in impact distance, the damage interference gradually disappeared. When impactors fell on the edge of the patch, the damage area caused by the first impact on the left half of the adhesive film gradually enlarged, and as the impact energy increased from 5 J to 12.5 J, the damage interference caused by the first impact on the second impact was gradually enhanced.

Enhanced compressive mechanical properties in stochastic bicontinuous porous structures

Inspired by the morphology of dealloyed nanoporous metals, we derive a novel open-celled porous structure with stochastic bicontinuous cell. The polymeric porous specimens are fabricated by additive manufacturing (AM), and the compressive mechanical properties and energy absorption capacity are explored experimentally. Results show that Young’s modulus, yield stress, plateau stress, and energy absorption characteristics are monotonically increasing with the relative density, obeying the Gibson-Ashby power correlation. Due to more defects generated in the specimen with smaller ligament diameter during AM, there is a significant decrease in Young’s modulus and a slight decrease in yield stress with the decrease of ligament diameter, which is opposite to the size effect in nanomaterials. Attributing to the bending and yielding deformation of ligaments, the stochastic bicontinuous porous solids show an enhanced energy absorption capacity. The ligament morphological structure has shown to be an additional factor affecting the mechanical responses of porous solids, and might magnify its sensitivity to structural characteristics. This study provides valuable idea and guidance for designing efficient open-celled porous structures in the promising application of energy absorption.

Wettability of two different artificial saliva substitutes on injection moulded heat polymerized acrylic resin and CAD-CAM acrylic resin: an in vitro study.

Aim: The purpose of this in vitro study was to evaluate the wettability of two different artificial saliva substitutes on injection moulded heat-polymerized acrylic resin and CAD-CAM acrylic resin and to compare these properties with natural saliva and distilled water.Materials and method: Forty heat polymerized (injection moulded) acrylic resin specimens and forty CAD-CAM acrylic resin specimens were fabricated with each specimen measuring 10x10x2mm. Four groups of liquids namely distilled water, Wet mouth™, Mouth Kote™ and human saliva were used. A contact angle goniometer was used to measure the contact angles. Two contact angle readings were obtained on the right side and on the left side of the test specimen. The observations were recorded and a mean of the two readings was calculated. The same procedure was repeated for all specimens (heat cure resin and CAD-CAM) with all the four test groups of liquids.Results: Contact angle measurements were significantly higher in Wet mouth™ and Mouth Kote™ solution of heat cure resin group compared to the CAD-CAM group (p-value<0.05 for both). Mouth Kote™ had lower mean contact angle (62.63 ± 4.59) than Wet mouth™ (77.46 ± 9.16) on CAD/CAM denture base resin. Mouth Kote also had lower mean contact angle (70.80 ± 4.79) than Wet mouth™ (97.77 ± 7.79) on injection moulded denture base resin.Conclusion: Mouth kote had better wettability than wet mouth on both CAD-CAM and injection moulded acrylic resin. Both the saliva substitutes had better wettability on CAD-CAM than on injection moulded acrylic resin.

Analysis and construction of a pneumatic-powered portable friction stir welding tool for polymer joining

ABSTRACT The increasing use of polymer products in transportation and almost all sectors is a distinctive sign of the current decade. On-site repair of defects along the spatial path are important advantages of a portable welding and repair system. The current article presented an in-house developed pneumatically powered portable set-up and tool for defect repair based on friction stir welding (FSW). The suggested tool can be used for welding polymer products such as car bumpers, motorboats, and polymer vessels. Further, acrylonitrile butadiene styrene (ABS) polymer specimens were joined by FSW and friction stir spot welding (FSSW), and the maximum temperature was monitored. FSW process parameters: rotational speed and traversing velocity, and FSSW parameter: rotational speed and dwell time, were varied, and the design of experiment-based investigations was carried out. Response surface method (RSM) and analysis of variance (ANOVA) were used to analyse the results. The acceptable results were obtained for rotational speed of less than or equal to 1100 rpm and welding velocity lower than 6.5 mm/min (for FSW). Good quality welds were obtained for dwell time equal to or higher than 25 s (for FSSW). The preferred temperature for a good quality weld was found to be 105°C in both processes.

Compression Behavior of Concrete Columns Strengthened with Fiber-Reinforced Inorganic Composites Based on Magnesium Phosphate Cement.

Fiber-reinforced polymer (FRP) composites have become attractive for strengthening and repairing deteriorated concrete structures. However, their poor high-temperature resistance and durability in some extreme environments, such as frequent water-vapor erosion and temperature changes, limit their application. Magnesium phosphate cement (MPC) has been used to repair damaged concrete due to its excellent high-temperature resistance and durability. Therefore, this paper aims to study the compressive behavior of concrete columns strengthened with fiber-reinforced inorganic polymer (FRiP) composites based on magnesium phosphate cement so as to evaluate the confinement effect. Twenty-one cylindrical specimens were prepared to examine the axial compressive behavior of carbon-fiber-reinforced inorganic polymer (CFRiP) specimens based on magnesium phosphate cement confined by one to three layers of carbon-fiber fabrics. They are compared with concrete specimens strengthened with epoxy-based FRP and unconfined concrete specimens. The test results show that compared with the unconfined concrete specimen, the strength of the CFRiP-strengthened specimens based on magnesium phosphate increases by 1.69-2.50 times, and their ultimate strain is enlarged by 1.83-3.50 times. The strength and ultimate strain of the CFRiP-strengthened specimens based on magnesium phosphate are approximately 95% and 60% of those of the specimens strengthened with epoxy-based FRP, respectively. A semiempirical model of concrete confined by the CFRiP system based on magnesium phosphate cement is also proposed. The theoretical prediction is finally compared with the experimental results, indicating that the developed model provides a prediction close to the test results.

An evaluation of elution of leachable components from composite resins after light curing by light emitting diode and halogen light: An in vitro study.

The purpose of our study was to determine the amount of eluted triethyleneglycol dimethacrylate (TEGDMA) and to compare the eluted TEGDMA in different composite resins after light curing with conventional halogen light curing unit and light emitting diode (LED). The present study was conducted on the two types of composite resins, which were divided equally into four groups - Group I: Denoted as Hybrid-LED, Group II: Denoted as Microhybrid-LED, Group III: Denoted as Hybrid-Halogen Group IV: Denoted as Microhybrid-Halogen. Polymerized specimens of hybrid and microhybrid composite resins were stored in air tight centrifuge tubes at 37°C for 24 h, then extract the monomers in high-performance liquid chromatography (HPLC) grade acetonitrile and water and incubated at 37°C for 24 h. All extracts were analyzed by HPLC. Eluted TEGDMA was detected by ultraviolet detector. The results obtained for TEGDMA were computed and analyzed using the one-way ANOVA and independent samples F-test at significance level 0.05. Elution of TEGDMA from all the samples of Group III (Hybrid-Halogen) was greatest and from Group II (Microhybrid-LED) was lowest. The sequence of TEGDMA elution was Group III > Group I > Group IV > Group II. From our results, we can conclude that the LED light curing unit may be more efficient than standard halogen light curing unit. The extractable quantities of composite resin components should be minimized. Furthermore, all ingredients of a dental composite should be declared by the manufacturers, in order to identify those substances in a product which may cause adverse side effects in patients and dental personnel.

Numerical investigations on mechanical properties of bio-inspired 3D printed geometries using multi-jet fusion process

PurposeThe purpose of this study is to find the best geometries among the cylindrical, enamel and honeycomb geometries based upon the mechanical properties (tensile test, compression test and shear test). Further this obtained geometry could be used to fabricate products like exoskeleton and its supporting members.Design/methodology/approachThe present research focuses on the mechanical testing of cylindrical, enamel and honeycomb-shaped parts fabricated through multi-jet printing (MJP) process with a wall thickness of 0.26, 0.33, 0.4 and 0.66 mm. The polymer specimens (for tensile, compression and shear tests) were fabricated using a multi-jet fusion process. The experimental results were compared with the numerical modelling. Finally, the optimal geometry was obtained, and the influence of wall thicknesses on various mechanical properties (tensile, compression and shear) was studied.FindingsIn comparison to cylindrical, enamel structures the honeycomb structures required less time to fabricate and had lower tensile, compressive and shear strengths. The most efficient geometry for fully functional parts where tensile, compressive and shear forces are present during application – cylindrical geometry is preferred followed by enamel, and then honeycomb. It was found that as the wall thickness of various geometries was increased, their ability to withstand tensile, compressive and shear loads also enhanced. The enamel shape structure exhibits greater strain energy storage capacity than other shape structures for compressive loads, and the strength to resist the compressive load will be lower. In the case of cylindrical geometries for tensile loading, the resisting area toward the loading will be higher in comparison to honeycomb- and enamel-based structures. At the same time, the ability to store the stain energy is less. The results of the tensile, compression and shear load finite element analysis using ANSYS are in agreement with those of the experiments.Originality/valueFrom the insight of literature review, it is found that a wide range of work is done on fused deposition modeling (FDM) process. But in comparison to FDM, the MJP provide the better dimensional accuracy and surface properties (Lee et al., 2020). Therefore, it is observed that past research works not incorporated the effect of wall thickness of the embedded geometries on mechanical properties of the part fabricated on MJP (Gibson, n.d.). Hence, in this work, effect of wall thickness on tensile, compression and shear strength is considered as the main factor for the honeycomb, enamel and cylindrical geometries.

Evolution of Statistical Strength during the Contact of Amorphous Polymer Specimens below the Glass Transition Temperature: Influence of Chain Length.

A comprehensive study of the statistical distribution of the auto-adhesion lap-shear strength (σ) of amorphous polymer-polymer interfaces using various types of statistical tests and models is a useful approach aimed at a better understanding of the mechanisms of the self-healing interface. In the present work, this approach has been applied, for the first time, to a temperature (T) range below the bulk glass transition temperature (Tgbulk). The interest of this T range consists in a very limited or even frozen translational segmental motion giving little or no chance for adhesion to occur. To clarify this issue, the two identical samples of entangled amorphous polystyrene (PS) with a molecular weight (M) of 105 g/mol or 106 g/mol were kept in contact at T = Tgbulk - 33 °C for one day. The as-self-bonded PS-PS auto-adhesive joints (AJ) of PSs differing in M by an order of magnitude were fractured at ambient temperature, and their σ distributions were analyzed using the Weibull model, the quantile-quantile plots, the normality tests, and the Gaussian distribution. It has been shown that the Weibull model most correctly describes the σ statistical distributions of the two self-bonded PS-PS AJs with different M due to the joints' brittleness. The values of the Weibull modulus (a statistical parameter) m = 2.40 and 1.89 calculated for PSs with M = 105 and 106 g/mol, respectively, were rather close, indicating that the chain length has a minor effect on the σ data scatter. The Gaussian distribution has been found to be less appropriate for this purpose, though all the normality tests performed have predicted the correctness of the normal distribution for these PS-PS interfaces.

Mechanical behavior of carbon and aramid fiber reinforced composites with various layups under tension

The present paper deals with investigation of mechanical properties of aramid and carbon fiber reinforced polymer specimens with different layups. Experimental results were obtained for tensile testing of ±45° laminate and tensile testing of orthotropic and quasi-isotropic layups. Digital image correlation was utilized to process the images of the specimen's surfaces captured throughout mechanical testing and to obtain the strain data. The localization of deformations in composites based on aramid and carbon fibers occurs in different ways. It depends on the layup, fabric or fiber has been used and inherent properties of fibers used. The pliability of aramid fibers, their high potential for deformation, as well as the woven of fibers into a fabric, leads to localization of deformations in the area of bundles due to the combined action of all these factors. Carbon fibers are also prone to strain localizations at low applied loads due to misalignments and the absence of preloading.

Influence of PBS, PBAT and TPS content on tensile and processing properties of PLA-based polymeric blends at different temperatures

PLA-based blends were prepared with different ratios of PBS, PBAT and TPS additives to adjust their mechanical and processing properties in various temperatures ( − 20 °C, 0 °C, 20 °C, 40 °C). Biodegradable polymeric specimens were obtained by preliminary extrusion and subsequent injection molding. Tensile properties, e.g., tensile strength, elongation at break, Young’s modulus and yield strength were evaluated. Next, melt flow and melt volume ratios were established. Softening, glass transition, cold crystallization and crystallization temperatures were determined with the use of the DSC method. Heat Deflection Temperatures for 1.8 MPa (HDT A) and 8 MPa (HDT C), as well as Vicat Softening Temperatures at 10 N (VST A) and 50 N (VST B), were examined. The manufacturing method was intentionally simplified to eliminate the need for additional mixture’s modification with compatibilizers. Each of the ductile compounds enhanced the deformability of PLA—most significantly in the case of PBAT and TPS, while at the same time reducing its tensile strength. The effect of the test conditions (strain rate and temperature) on the specimens was evaluated in order to determine the stability of the manufactured blends in dependence on these parameters.

Efficient characterization on the interlayer shear strengths of 3D printing polymers

Shear strength measurement becomes increasingly important because three-dimensional (3D) printing materials are used in load-bearing structures subjected to a combined normal and shear stress state. Hence, this paper presents a combined experimental and numerical investigation of the interlayer shear strength measurement approach, and its application to four kinds of 3D printing polymers including acrylonitrile butadiene styrene (ABS), polycarbonate (PC), and polylactic acid (PLA) made with fused deposition modeling (FDM), and polyamide 12 (PA12) made with selective laser sintering (SLS). First, a traditional Iosipescu shear specimen was employed to validate the uniform shear strain field using digital image correlation. Second, a new necking-shaped shear specimen was proposed to measure the shear strength efficiently with the aid of an effective alignment assistant beam. Third, 3D finite element analysis was conducted to highlight the stress comparisons of the Iosipescu shear specimen and the necking-shaped shear specimen. In order to quantify the anisotropic strengths, three kinds of shear specimens with different build directions were designed and tested. The results demonstrated that the minimum shear strength of a 3D printing polymer specimen was the interlayer shear strength when the shear force was acting along the printing surface. Our measurement was consistent with the shear strength measurements of the same type of 3D printing PA reported by other researchers. Moreover, our measurement was more conservative and accurate due to the pure shear stress state of all specimens.