Experimental Tensile Tests Research Articles

Evaluation of the infill design on the tensile properties of metal parts produced by fused filament fabrication

Additive Manufacturing (AM) applications have expanded significantly from rapid prototyping to high-end products such as complex spare parts. AM has enabled advantages of reduced material usage, geometric freedom, and production automation, shaping the future of the manufacturing industries. With the rapid expansion of AM applications, feedstock materials have developed noticeably, from polymers and ceramics to metals and composites. The progress in metal feedstock material discoveries has empowered the exploration of implementing new AM technologies. Fused Filament Fabrication (FFF) is one of the most common and cost-effective material extrusion AM technologies. This study explores the effect of the infill pattern on the tensile mechanical properties of metal parts produced via FFF, using two feedstock materials, 17-PH stainless steel and copper. Two approaches are designed to investigate the results: experimental tensile test, and Finite Element Analysis (FEA) with digital twin reconstruction method. Results show that 17-4 PH Stainless Steel samples with a triangular infill exhibited a 42% drop in ultimate tensile strength compared to solid infill. However, it also revealed a 34% reduction in mass, cost saving of 36%, and a faster fabrication with a 25% reduction in lead time. At the same time, copper samples with triangular infill exhibited a 22% drop in ultimate tensile strength and a 12% mass reduction. However, it revealed a similar lead time with only a 3% reduction. A Scanning Electron Microscope (SEM) was used to investigate the parts’ internal structure and average pore size, to understand the failure mode of the test specimens.

Damage detection in GFRP composite structures by improved artificial neural network using new optimization techniques

Structural damage identification has been researched for a long time and continues to be an active research topic. This paper proposes the use of the natural frequencies of a novel composite structures made of glass fibre reinforced polymer (GFRP). The proposed methodology consists of an improved Artificial Neural Network (ANN) using optimization algorithms to detect the exact crack depth. In the first step, the characterization of fabricated material is provided to determine Young's modulus using an experimental static bending test, tensile test and modal analysis test. Next, numerical validation is performed using commercial software ABAQUS to extract more data for different crack locations in the structure. The comparison between experimental and numerical results shows a good agreement. ANN has been improved using recent optimization techniques such as Jaya, E-Jaya, Whale Optimization Algorithm (WOA) and Arithmetic Optimization Algorithm (AOA) to calibrate the influential parameters during training. After considering several scenarios, the results show that the accuracy of enhanced Jaya is better than that of other optimization techniques. This study on crack identification using improved ANN can be used to investigate the safety and soundness of composite structures.

Modeling Materials Coextrusion in Polymers Additive Manufacturing.

Material extrusion additive manufacturing enables us to combine more materials in the same nozzle during the deposition process. This technology, called material coextrusion, generates an expanded range of material properties, which can gradually change in the design domain, ensuring blending or higher bonding/interlocking among the different materials. To exploit the opportunities offered by these technologies, it is necessary to know the behavior of the combined materials according to the materials fractions. In this work, two compatible pairs of materials, namely Polylactic Acid (PLA)-Thermoplastic Polyurethane (TPU) and Acrylonitrile Styrene Acrylate (ASA)-TPU, were investigated by changing the material fractions in the coextrusion process. An original model describing the distribution of the materials is proposed. Based on this, the mechanical properties were investigated by analytical and numerical approaches. The analytical model was developed on the simplified assumption that the coextruded materials are a set of rods, whereas the more realistic numerical model is based on homogenization theory, adopting the finite element analysis of a representative volume element. To verify the deposition model, a specific experimental test was developed, and the modeled material deposition was superimposed and qualitatively compared with the actual microscope images regarding the different deposition directions and material fractions. The analytical and numerical models show similar trends, and it can be assumed that the finite element model has a more realistic behavior due to the higher accuracy of the model description. The elastic moduli obtained by the models was verified in experimental tensile tests. The tensile tests show Young's moduli of 3425 MPa for PLA, 1812 MPa for ASA, and 162 MPa for TPU. At the intermediate material fraction, the Young's modulus shows an almost linear trend between PLA and TPU and between ASA and TPU. The ultimate tensile strength values are 63.9 MPa for PLA, 35.7 MPa for ASA, and 63.5 MPa for TPU, whereas at the intermediate material fraction, they assume lower values. In this initial work, the results show a good agreement between models and experiments, providing useful tools for designers and contributing to a new branch in additive manufacturing research.

Experimental Analysis of Transseptal Puncture to Investigate the Mechanical Properties of Fossa Ovalis

Background/Objective: Optimization of needle characteristics for trans-septal puncture is of paramount importance to reduce the extent of tissue deformation. This was achieved by studying the mechanical behavior of fossa ovalis (FO) in lamb hearts. The fossa ovalis tissue samples obtained after dissection were subjected to experimental indentation and tensile tests to determine tissue deformation. Methods: Lamb hearts (n = 20) were dissected to obtain fossa ovalis tissue samples. These were subjected to indentation and tensile tests to determine the puncture and rupture forces respectively. Indentation tests were performed using two different indenters: A steel indenter with a hemispherical tip and a Brockenbrough (BRK) needle (bevel tip). Tensile tests were formed using Zwick Roell (Z005) tensile machine at 100 N load cell. ImageJ analysis was also performed to determine the diameter and shape of FO. Results: Indentation results demonstrated that the hemispherical indenter requires a greater punch force compared to the puncture force with the BRK needle. The mean punch force of the hemispherical indenter (15.57 N) was nearly 3 times greater than the puncture force of the BRK needle (5.47 N). Variations between the two indenters provide an insight into the importance of device geometry on trans-septal procedures. The tensile test results illustrated a typical failure pattern with a toe region, linear region, and failure region. The mean rupture force determined was 10.51 N. ImageJ analysis confirmed an oval shape of FO and the diameters measured were in the range 9.0–15.3 mm. Conclusions: The mechanical aspects of fossa ovalis in lamb hearts were successfully studied through a series of experimental indentation and tensile tests. This study serves as a guide to dissecting the challenging FO sample. The procedures for indentation and tensile tests are detailed with common experimental challenges encountered addressed. The correlation of the parameters involved in these experimental tests to the collagen fiber orientation in tissues is also discussed, providing an insight into the deformation of tissues and variations in fiber orientation before and after trans-septal procedures.

Multiscale modelling of material degradation and failure in plain woven composites: A novel approach for reliable predictions enabled by meta-models

In this paper a multiscale method for modelling damage evolution at meso and macro scales with application to plain woven composites is presented for the first time. The method couples the macro and micro-scale simulations using an averaging theorem in which the computations in the two scales are performed simultaneously. Unlike the local–global approach, the developed multiscale analysis is carried out over the entire macro domain rather than a predefined segment. To address the computational challenges in multiscale damage analysis, the proposed method a) employs a non-local approach in constructing the macro–micro interface to avoid the pathological localisation effect introduced by microdamage at the macro continuum; b) reduces the considerable computing effort incurred by the non-linear behaviours in multiscale damage analysis by the introduction of machine learning meta-models. Experimental tensile tests conducted are shown to be in good agreement with the proposed method for both on-axis and off-axis load directions. The biaxial loading cases are also investigated with the results illustrated by the failure envelopes and compared with the existing damage criteria. Finally, an example of open-hole tension test is presented to demonstrate an application of the proposed method to model progressive damage and crack propagation in composite plates.

Fitting mechanical properties of the aortic wall and individual layers to experimental tensile tests including residual stresses

The authors have observed that a stress-strain curve for uniaxial tension of an aortic intact wall cannot be simply obtained by combining the strain energy functions of the three individual aortic layers – intima, media and adventitia – even taking into account the interaction among the three layers; the strain energy functions of the three layers are obtained fitting tensile tests on strips from the individual layers. Due to the layer separation, the residual stresses are released and thus they do not affect the stress-strain curves of the individual layers. The present study shows that it is instead possible to fit the intact wall experimental curves with the combination of the strain energy functions of the three individual layers if residual strains are added. The residual strains are used as optimization parameters with specific constraints and allowing for the buckling (wrinkling) of the intima under unpressurized condition of the aortic wall, as experimentally observed. By varying these parameters in the experimentally observed range of values, it is possible to find a solution with the combined responses of the individual layers matching the experimental stress-strain curves of the intact wall.

Thermoplastic elastomer composite strips with damage detection capabilities for self-healing elastomers

Self-healing materials can increase the lifetime of products and improve their sustainability. However, the detection of damage in an early stage is essential to avoid damage progression and ensure a successful self-healing process. In this study, self-healing sensor composite strips were developed with the embedding of a thermoplastic styrene-based co-polymer (TPS) sensor in a self-healing matrix. Piezoresistive TPS sensor fibers composites (SFCs) and 3D printed sensor element composites (SECs) were fabricated and embedded in a self-healing matrix by lamination process to detect damage. In both cases, the value of the initial resistance was used to detect the presence of damage and monitor the efficiency of healing. A higher elongation at fracture could be achieved with the extruded sensor fibers. However, for the composite strips the SECs could achieve a higher elongation at fracture. Mechano-electrical analysis revealed that the strips maintained a monotonic, reproducible response after the healing of the matrix. The SFCs had significantly lower drift of the sensor signal during cyclic mechanical analysis. Nevertheless, on a tendon-based soft robotic actuator, the SECs obtained a drift below 1%. This was explained by the lower deformation (e.g.) strain in comparison to the tensile test experiments.

A probabilistic virtual process chain to quantify process-induced uncertainties in Sheet Molding Compounds

The manufacturing process of Sheet Molding Compound (SMC) influences the properties of a component in a non-deterministic fashion. To predict this influence on the mechanical performance, we develop a virtual process chain acting as a digital twin for SMC specimens from compounding to failure. More specifically, we inform a structural simulation with individual fields for orientation and volume fraction computed from a direct bundle simulation of the manufacturing process. The structural simulation employs an interpolated direct deep material network to upscale a tailored SMC damage model. We evaluate hundreds of virtual specimens and conduct a probabilistic analysis of the mechanical performance. We estimate the contribution to uncertainty originating from the process-induced inherent random microstructure and from varying initial SMC stack configurations. Our predicted results are in good agreement with experimental tensile tests and thermogravimetric analysis.

Experimental investigation and numerical prediction of rupture in SS304 stainless steel sheet under tension

This work is focused on prediction of rupture in the tensile tests of SS304 stainless steel sheet. The tensile test experiments were performed up to rupture and the strain was measured using extensometer and digital image correlation (DIC) system. The experimental results obtained from the tensile tests were utilized for the numerical simulation. In the numerical simulation, four macroscopic rupture criteria were used to predict rupture. The numerical results show the good agreement with the experimental results. Damage factor was calculated using the macroscopic rupture criteria in numerical simulation. The critical values of the damage factor based on the macroscopic criteria were obtained at rupture in simulation. These values are unique for all the mechanical tests and can be utilized for prediction of rupture in numerical simulation of mechanical tests. This study shows that Oh, Brozzo and Ayada criteria have good agreement for strain at rupture whereas Rice-Tracey criterion doesn’t show any agreement within the range of triaxiality from 0 to 0.66.

A mixed mode phase-field model of ductile fracture

We present the first mixed mode phase-field model of ductile fracture. The contribution of crack opening and shearing deformations to the propagation of a crack is expressed by introducing two phase fields. Constitutive relations are then introduced to couple and distinguish these phase fields. Special attention is given to the maximum shear stress and its effect on the development of fractures. The proposed model is validated by tensile testing experiments found in the literature on Al 2024 T-351. Model predictions of the crack path and load-displacement response are compared to a plane-strain tension experiment, a round bar tension experiment and a notched round bar tension experiment. The model is shown to accurately capture the slant and cup-cone crack paths as well as force-displacement curves.

Patient–Specific Immersed Finite Element–Difference Model of Transcatheter Aortic Valve Replacement

Transcatheter aortic valve replacement (TAVR) first received FDA approval for high-risk surgical patients in 2011 and has been approved for low-risk surgical patients since 2019. It is now the most common type of aortic valve replacement, and its use continues to accelerate. Computer modeling and simulation (CM&S) is a tool to aid in TAVR device design, regulatory approval, and indication in patient-specific care. This study introduces a computational fluid-structure interaction (FSI) model of TAVR with Medtronic’s CoreValve Evolut R device using the immersed finite element-difference (IFED) method. We perform dynamic simulations of crimping and deployment of the Evolut R, as well as device behavior across the cardiac cycle in a patient-specific aortic root anatomy reconstructed from computed tomography (CT) image data. These IFED simulations, which incorporate biomechanics models fit to experimental tensile test data, automatically capture the contact within the device and between the self-expanding stent and native anatomy. Further, we apply realistic driving and loading conditions based on clinical measurements of human ventricular and aortic pressures and flow rates to demonstrate that our Evolut R model supports a physiological diastolic pressure load and provides informative clinical performance predictions.

Analysis and optimization of FFF process parameters to enhance the mechanical properties of 3D printed PLA products

Abstract In this work, the combined effects of fused filament fabrication (FFF) process parameters on the mechanical properties of 3D printed PLA products have been determined by focusing on the tensile strength at R 2 (97.29%). ASTM D638 test standard is used for the preparation of specimens for tensile tests. The optimization technique has been used to determine the optimal combinations of FFF process parameters for the validation of experimental tensile tests and computational fluid dynamics (CFD) simulations. From the results obtained the optimum cooling fan speed of 79.3%, extrusion temperature of 214.4 °C, printing speed of 75.9 mm/s, raster width of 0.4814 mm, and shell number 5 were determined with a 2.266% error of the tensile strength (45.06 MPa). SEM morphology examination shows that the fabricated part cooled at 80% cooling fan speed illustrates good inter-layer bond strength which is also confirmed by CFD temperature distributions analysis.

A simplified stress–strain relationship for the mechanical behavior of corroded prestressing strands: The SCPS‐model

AbstractThis article presents a simplified stress–strain relationship for the definition of the mechanical behavior of prestressing strands subjected to chloride‐induced corrosion, named SCPS‐model (Simplified Model for Corroded Prestressing Strands). The constitutive law adopts the equivalent spring model, that reproduces the overall behavior of a corroded strand by summing the contributions of each wire, assumed as a spring working in parallel to the others. The SCPS‐model is designed for the application in the daily engineering practice; to this aim, it is based on a single input parameter that is the maximum penetration depth of the most corroded wire. Following a detailed description of the model formulation and parameters, the article shows the validation of the stress–strain relationship through several comparisons with experimental tensile test outcomes coming from scientific literature. Finally, a statistical analysis of the dimensionless ratio of experimental and analytical results in terms of ultimate corroded strength and strain is carried out to demonstrate the effectiveness of the SCPS‐model. Concluding, the accurate and safe side prediction of the residual mechanical behavior of corroded prestressing strands is proposed using the SCPS‐model.

Identification of a soft matrix-hard inclusion material by indentation

A new procedure for identifying the mechanical behavior of individual phases within a bi-material (matrix-particles) is presented. The case of AlSi10Mg (large globularized Si-rich particles surrounded by an α-Al phase) processed by additive manufacturing and post-treated is taken as a typical example. Grids of nano-indentation tests are performed at different locations on the nanocomposite using a Berkovich indenter and show an impact of the hard inclusions on the experimental curves. The elastoplastic properties of the matrix are identified based on the lowest load–indentation depth curves. Several representative finite element (FE) models demonstrate the influence of the particles on the nano-indentation response. The capacity of the FE model to predict the indentation curve of a cube corner indenter experiment and the Berkovich grid result scattering was checked. A representative volume element (RVE) based on a scanning electron microscope (SEM) image is defined. The identified material parameters of the α-Al phase and Si phase, it allows the prediction of the stress-strain curve of a macroscopic experimental tensile test.

3D printing of alginate/thymoquinone/halloysite nanotube bio-scaffolds for cartilage repairs: experimental and numerical study.

One of the newest advances in 3D printing is the printing process of bio-scaffolds. The 3D printing of true materials for cartilage repairs accelerates cell growth and proliferation. In this study, a novel biomaterial was developed for the 3D printing of cartilage scaffolds composed of alginate, thymoquinone and halloysite nanotube. Calcium chloride was used as a cross-linker to form hydrogels. Experimental and numerical studies such as scanning electron microscopy, experimental tensile tests, and compression tests, chondrocyte cell seed, and MTT assay were also done. According to the results, alginate and halloysite nanotube increased the printing quality and mechanical performance of biomaterials. Tensile strength in bio-ink with the 30mg/ml of alginate, 40mg/ml of halloysite nanotube with 5% of thymoquinone increased up to 372 ± 42kPa, while compressive stress reached 894 ± 39kPa. Numerical results indicated that tensile and compressive properties of the scaffold structure depend on the space between printed rows. The best structure was obtained when the distance of rows was chosen at 0.4mm, and the nozzle diameter was 0.3mm. Finally, the biomaterial with the 30mg/ml of alginate, 40mg/ml of halloysite nanotube with 5% of thymoquinone showed a high mechanical and biological performance, compared to pure alginate bio-scaffolds. Biomaterials included alginic acid sodium salt/thymoquinone/halloysite nanotube mixed and 3D printed in high technology bioprinter, then mechanical and biological properties of printed bio-scaffolds obtained by different experimental tests.

A Study on Multi-Objective Optimization of Large Deformable Elastic Plates

Metallic yielding dampers are damaged early before the main frame during earthquakes and take over the damage of the main frame. Under the assumption of the main frame elasticity, both maximum and residual deformation are expected to be reduced. However, the main frame may be damaged, and the assumption of the main frame elasticity may not hold under major earthquakes. However, large deformable elastic plates have larger yielding deformation than standard steel core plates of the damper and can be used as braces to reduce the seismic response of buildings. This study presents a simple definition of design variables for a topology optimization problem involving large deformable elastic plates with rectangular shapes. As bi-objective functions, yielding deformation and yielding force capacity maximization were used. The optimization results were compared with the findings of a previous study. Finally, the efficacy of the braces was verified by experimental tensile tests. The obtained results are as follows. (1) A distinct trade-off relationship was obtained between tensile yielding deformation and tensile yielding load through muti-objective optimizations using the proposed formulation. (2) The Pareto fronts using the proposed formulation were almost identical to the findings of the previous study. (3) While the experimental test results of yielding tensile load are overestimated by the analysis results by the 10 mm rough grid elements, the test results almost correspond to reanalysis results with the 2.5 mm fine grid elements.

Comparison of Models to Predict Mechanical Properties of FR-AM Composites and a Fractographical Study

Continuous fiber-reinforced additive manufacturing (cFRAM) composites improve the mechanical properties of polymer components. Given the recent interest in their mechanical performance and failure mechanisms, this work aims to describe the principal failure mechanisms and compare the prediction capabilities for the mechanical properties, stiffness constants, and strength of cFRAM using two distinct predictive models. This work presents experimental tensile tests of continuous carbon fiber AM composites varying their reinforced fraction, printing direction, and fiber angle. In the first predictive model, a micromechanical-based model for stiffness and strength predicts their macroscopic response. In the second part, data-driven models using different machine learning algorithms for regression are trained to predict stiffness and strength based on critical parameters. Both models are assessed regarding their accuracy, ease of implementation, and generalization capabilities. Moreover, microstructural images are used for a qualitative evaluation of the parameters and their influence on the macroscopic response and failure surface topology. Finally, we conclude that although predicting the mechanical properties of cFRAM is a complex task, it can be carried on a Gaussian process regression and a micromechanical model, with good accuracy generalized onto different process parameters specimens.

Numerical simulation on mechanical properties and damage behavior of CFRP with self-healing microvascular channels

In this study, 3D representative volume element models with microchannels were established based on measured data. And the periodic boundary conditions were moderately modified to adapt to the actual constraints of the studied object. The effects of different microvascular parameters on the tensile and compressive properties of composites were studied. And the damage pattern of carbon fiber as the main load-bearing phase under the force was analyzed. The models were verified by tensile testing and micromorphology experiments. The research results are of application to the design and analysis of CFRP laminates containing similar microchannel structures.

Numerical and Experimental Investigations on the Mechanical Properties of Milled Specimens from an AA7020 Tube

The reduction of weight is crucial in the automotive sector to reach a lower energy consumption and an increased range, especially for electrically powered vehicles. In this regard, body-in-white parts offer a high potential for the application of lightweight construction. The required weight savings can be achieved by implementing parts with a high strength-to-weight ratio. A promising approach is the combination of lightweight materials and lightweight design, which can be realized by tubular components made of high strength aluminum. Due to their structural stiffness and high crashworthiness, those structures are often used as safety-relevant car body components. However, the material characterization of tube profiles is a major challenge, which in turn impedes an accurate numerical simulation and precise process design. In contrast to flat semi-finished parts, various effects of the production process and the geometry, regarding the stress state under load, must be taken into account. For this purpose, adapted testing methods considering the geometrical and mechanical properties of the tubular parts have to be investigated, in order to generate an accurate material model and process design. Within this research work, tubular components made out of AA7020 in W-temper condition were used to analyze the mechanical properties. In this regard, several tensile specimens are milled from a tube, so they also have a curvature profile. The experimental tensile tests have been performed at different strain rates by using an universal testing machine from type Gleeble 3500. To ensure a proper measurement of the mechanical properties, the clamping jaws of the testing machine are adjusted to the curved samples. The investigated material parameters are subsequently transferred to an FE-Model with curved specimen to enable an accurate prediction of the forming behavior. In addition, an FE model of a flat tensile specimen was also created for comparison, in order to gain a profound knowledge regarding the influence of the geometric and mechanical properties of tubular components.

Experimental and Numerical Investigation of Intact, Defective and Repaired Countersunk Composite Joints under Tensile Loading.

Bolted joints are commonly used for assembling carbon fiber/resin composite structures. Since drilling may generate defects at hole edges which affect mechanical properties, it is of great engineering significance to develop proper repair methods to restore the mechanical properties of the defective parts. However, there are few studies on hole edge defects and their repair methods. Therefore, a novelty short fiber filling repair method was proposed to repair defective holes in this study. The mechanical properties of intact, defective and repaired countersunk composite joints were compared and investigated. Experimental tensile tests showed that defective joints had lower initial stiffness and failure loads compared to intact joints, while the mechanical properties were effectively restored after repair. Three-dimensional finite element models were also established to analyze the damage process of the joints. Results of numerical modelling were consistent with the experimental results. The simulations showed that changes in contact behaviors and local deformations caused by hole edge defects led to the low initial stiffness and stiffness transition point of the joint, while this phenomenon was reduced after repair. Additionally, despite different joint types, laminate failure mainly occurred around the hole and countersink.