Measurement of elastic properties of materials employing 3-D DIC in a Cornu’s experiment

Measurement of elastic properties, especially the Poisson's ratio, utilizing non-contact techniques in a tensile experiment is very challenging. This is primarily due to the poor spatial resolution and the large strain noise inherent to these techniques. The difficulty level increases many folds when Poisson's ratio of less elongating, stiffer, and/or brittle materials, like ceramics and ablatives, is measured. This paper reports a newer approach that employs 3-D digital image correlation (3-D DIC) in a Cornu's experiment to enable accurate measurement of elastic properties in a single test. The deflection field obtained from 3-D DIC in the form of anticlastic surfaces during Cornu's experiment is utilized for determining Poisson's ratio. In the same experiment, the elastic modulus is estimated using the center point deflection method. The proposed methods are validated with standard materials and extended to newly developed materials. Cornu's method with 3-D DIC can provide the elastic properties with ease and has many advantages over other conventional techniques.

An Inverse Method for Measuring Elastoplastic Properties of Metallic Materials Using Bayesian Model and Residual Imprint from Spherical Indentation

In this paper, an inverse method is proposed for measuring the elastoplastic properties of metallic materials using a spherical indentation experiment. In the new method, the elastoplastic parameters are correlated with sub-space coordinates of indentation imprints using proper orthogonal decomposition (POD), and inverse identification of material properties is solved using a statistical Bayesian framework. The advantage of the method is that model parameters in the numerical optimization process are treated as the stochastic variables, and potential uncertainties can be considered. The posterior results obtained from the measuring method can provide valuable probabilistic information of the estimated elastoplastic properties. The proposed method is verified by the application on 2099-T83 Al-Li alloys. Results indicate that posterior distribution of material parameters exhibits more than one peak region when indentation load is not large enough. In addition, using the weighting imprints under different loads can facilitate the uniqueness in identification of elastoplastic parameters. The influence of the weighting coefficient on posterior identification results is analyzed. The elastoplastic properties identified by indentation and tensile experiment show good agreement. Results indicate that the established measuring method is effective and reliable.

Research on fracture behaviour of the adhesive sealant based on energy failure criterion for TFT-LCD

The adhesive sealant is a crucial structure connecting color filters and thin film transistors in liquid crystal panels. Research on the fracture progress of the connection structure is heavily needed in reliability evaluation engineering. In this work, three types of adhesive sealants with different widths were tested by the uniaxial tensile experiment to obtain their fracture process curves, which conformed to the brittle fracture characteristics described by the bilinear cohesion zone model. Then, according to the theory of engineering fracture mechanics, the Dugdale-Barenblatt plastic zone model was employed to analyze the adhesive sealant with hole defects, and it was simplified to mode ? fracture mechanics problem. Calculating with finite element numerical simulation, the numerical relationship between the stress field of the internal defect and the external stress of the material was obtained, and the brittle fracture behavior model was deduced as related to the defect size. Applying the model to the adhesive sealant, the average error of the model value after the correction was reduced from 7.98-12.13% to 6.84-7.53%, and the overall error was only within 15%. The model includes the material’s basic characteristics and the defect’s size that affect the fracture process, provides a theoretical basis for predicting the fracture of the sealant and improving the strength of bonded joints, thus is of great significance for material application and fracture analysis in engineering.

Response Analysis of a Scraper Conveyor under Chain Faults Based on MBD-DEM-FEM

To tackle the difficulty in obtaining the response data of chain and bulk coal under chain faults, this paper uses a new method for the fault simulation of scraper chains based on the coupling of multi-body dynamics (MBD), discrete element method (DEM), and finite element method (FEM). With the force and stacking angle as response values, the contact parameters of bulk coal were revised using a rotary transport test. The simplified DEM-MBD model was verified from the resistance using the point-by-point method. The static structure model of the chain was verified by the chain tensile experiment. The DEM-MBD coupling results show that when the chain is stuck or broken, the dynamic properties of the chain and bulk coal fluctuate sharply, and the wear of the medium plate increases. Based on the DEM-MBD coupling results and the DEM-FEM unidirectional coupling, the stress, strain and life were acquired, and were verified experimentally. Regarding the fracture, the Plackett-Burman test was used to determine that the crack depth, initial angle, and tensile load significantly affect the stress intensity factor (SIF). The quadratic model between significant factors and SIF was constructed using the response surface method, which provides a reference for the simulation of the scraper conveyor, the fault mechanism, and the optimization of the design of the chain.

Prediction of Tensile Strength of 3D Printed Bronze PLA Part Using Response Surface Modelling

Background - 3D printing is a dynamic process with many process parameters influencing the product, including the type of the material; it is often difficult to understand the combined influence of these parameters. Purpose - The tensile strength of 3D printed parts is important for the functionality of components. The effects of process parameters on tensile strength must therefore be examined. The objective of this study is to develop a response surface model (RSM) to predict the final quality of a 3D printed bronze part from a different set of input parameters. Methods - The tensile test specimen was built in a Makerbot 3D printer with bronze polylactic acid (PLA) material. The three controllable input parameters were; thickness of layers, number of shells, and infill density. The three levels of layer thickness were 0.1mm, 0.2mm and 0.3mm. The number of shells was 2, 3 and 4. The infill densities were 20%, 30% and 40%. A tensile experiment tested the strength of the specimens. RSM is a statistical approach for modelling and analyzing how different variables affect the response of interest, and for optimizing it. Results - The result obtained shows that the specimen with a high layer thickness of 0.3mm and infill density of 40% is the best among all the other parameters. Finally, the regression equation produced was used for random values of layer thickness, the number of shells, and infill density, to see whether the values obtained from the tests fall into the range of experimental data. Conclusion - Infill density and layer thickness are the two criteria that significantly influence the tensile property. The number of shells has the least influence on the tensile property. However, the best tensile strength is the part printed with higher infill density, a greater number of shells, and higher layer thickness.

Dry vs. wet testing: quasi-static tensile experiment setup for polymer based biomaterials

Polymer materials can be manufactured with high reproducibility and do offer the potential for chemical modification. This enables matrix property modification and fine-tuning of several material characteristics, such as tissue-implant interaction, inflammatory potential or susceptibility to biofilm formation. Whereas manufacturing protocols are crucial for the resulting material properties, also the evaluation in terms of performance and safety has to be considered. Regarding this, both, temperature and composition of test medium may affect the physicochemical properties of implant materials. The present study addresses the influence of test medium compared to dry test conditions, each at two different temperatures, on the mechanical properties of elastomeric film and nonwoven materials.

Selective Laser Melting of 316L Stainless Steel: Influence of Co-Cr-Mo-W Addition on Corrosion Resistance

The selective laser melting (SLM) of o-Cr-Mo-W/316L composite with 10wt% Co-Cr-Mo-W addition to 316 L stainless steel (SS) powder is produced to explore it’s the corrosion behavior. The tensile experiment of SLM composites is also measured to investigate the difference between the two samples. The optimum parameters of SLM 316 L SS and it’s composite samples are obtained by adjusting laser power and scanning speed with the relative density of 99.04 ± 0.69 and 99.15 ± 0.43. The yield strength of samples is increased from 731.96 MPa to 784.09 MPa after doping, and no obvious crack or fracture failure in the tensile samples are observed, indicating that the excellent plasticity is still maintained. The corrosion resistance of samples is improved largely with an order of magnitude lower corrosion current density than that of 316 L SS and increasing of 277 mv of epit Ep. The addition of Cr element in the doped powder contributes to the formation of the passivated film containing Cr. The different pitting corrosion pit occurs mainly around the pre-existing pores of the powder and further extends outward to form pits with the increase of voltage.

Structural Design and Tensile Experiment of Connection Node between acrylic and Stainless Steel

Acrylic are widely used as load-bearing structural parts. In this study, the structural design, finite element analysis (FEA) and tensile experiment of the connection node of the acrylic spherical vessel designed for Jiangmen Underground Neutrino Observation (JUNO) are carried out. The acrylic connection node needs to withstand a tensile load of 90 kN for 20 years, and its ultimate bearing capacity is required to be 6 times the working load. Under working load, the stress of the acrylic structure should be less than 3.5 MPa. In the study, a connection node connecting acrylic and stainless steel is designed. By embedding the steel ring in the acrylic structure to connect with the support rod, the acrylic connection node can withstand high loads. A 1/4 symmetric model of connection node is established, and the FEA method is used to solve nonlinear problems such as material nonlinearity and frictional contact. The results of FEA show that the maximum principle stress of the connection node is about 2.92 MPa. By comparing the stress of the FEA results with the experimental results, the relative difference is 7.24 %, indicating that the FEA results are credible. The experiment results also show that the ultimate tensile load of the connection node can reach 1000 kN, which is about 11 times the working load. The breakdown of the connection node occurs at the sharp corner of the groove instead of the maximum stress point. Through the design, simulation and experiment of the connection node, for the brittle materials such as acrylic, the structure should avoid the defects such as sharp corner.

Processing and properties of hollow glass microsphere particulate-filled PA2200 composites produced by selective laser sintering

Selective laser sintering (SLS) to prepare composites by adding filler into polymer is an effective method to save costs and reinforce the sintered parts. This article investigated the fabrication of PA2200 composites filled with different volume fractions of hollow glass microsphere (HGM) by SLS. HGM was prepared by silane coupling agent surface treatment. The particle size distribution, microstructure, thermal and mechanical properties of PA2200/HGM composites were studied by scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and tensile experiment. The results indicated that the density of the composite was significantly reduced compared to the neat PA2200 and the density decreased with the HGMs content increasing. HGM improved the warping deformation in the process of sintering. The tensile modulus increased while tensile strength and elongation at break decreased as a function of HGM volume fraction in a certain range. This work indicated that thermal properties and tensile properties of polyamide-matrix composites can be reinforced by adjusting HGM content, and PA2200/HGM composite powder is a good material for SLS with less density and lower cost.