More specifically, tensile tests are conducted on a single material and a double material sample to analyze the influence of different experiment variables that can contribute to the improvement of the mechanical properties of 3D printed products. Statistical methods are then examined to estimate the maximum tensile strength of the 3D printed product before the actual product is printed. We use the Gaussian process to estimate non-stationary mechanical properties and their uncertainties related to the infill rate.
Motivation
Research Objectives
Outline of the Thesis
Mechanical Properties of 3D Printed Specimen
Carbon Fiber Reinforced Composites for Additive Manufacturing
Regression Analysis
Reliability Analysis
Background
For the detailed printing process, the sheet of material is first attached to the base structure with a heated roller and then laser cut and laminated. At the end of the stack, the platform goes down again, the new fabric sheet comes back onto the platform, and the platform to attach to the model under construction is raised again. 3D printing by the LOM method is advantageous in that the material used is cheaper than metal or photocurable resin used in other 3D printers, but it has a disadvantage in that the durability and flexibility of the printed product is poor than due to the nature of the material.
In the case of nano/microstructures, biotechnology and molds, stereolithography apparatus (SLA) systems are typical, which are favorable for the production of finer shapes. Among them, a nanometer-scale fabrication technology has recently been developed to overcome the diffraction limit of the light source and to study the fabrication of three-dimensional microstructures using two-photon absorption, which is favorable for the fabrication of three-dimensional microstructures with a precision of 100 nm. The printed substrate to be fabricated and the support to support the printed substrate are formed on the build platform, and each time layers are stacked, the build platform moves to represent the position to be stacked next.
In the scanning method, a point of light focused on a point is scanned according to the external shape of an object to form a solidified layer, and then the interior is filled in a lattice manner in a lattice manner and cured. However, it has been difficult to use the liquid crystal display for a long time because it contains a substance that deteriorates from UV rays, which is mainly used as a light source.
Objectives
Single Nozzle 3D Printer
- Experimental Setup
- Key Manufacturing Factors
- Results
- Analysis
In this thesis, the tensile tests for the tensile strength of the samples are carried out using a universal testing machine (Instron 5982) in Figure 8 with a constant strain rate of 2 mm/min [20]. The test piece exhibits a greater tensile strength in the x direction compared to that in the 45° direction. Considering the material properties of the sample, PLA showed better properties in terms of tensile strength than ABS.
An optical microscope view was used in this paper to understand these results of why the x-direction specimen has a stronger ultimate tensile strength than the 45º direction in the first experiment. The horizontal and vertical Ra of the sample with respect to the x-direction were 1.938 μm and 2.052 μm. The horizontal and vertical Ra of the sample relative to the 45º direction were 0.147 μm and 3.014 μm.
The fact that the specimen with respect to the x-direction receives less tensile strength provides an explanation for the reason why the specimen with x-direction has a stronger ultimate tensile strength than that of the 45º direction in the first experiment. To see why the PLA sample exhibits a stronger tensile strength than ABS, enlarged images of the fracture surface for each sample after the tensile test are shown in Figure 22 .
Dual Nozzle 3D Printer
Experiment for Dual Materials
The results of the average stress-strain test were expressed as a graph of the dependence of strain on stress. The tensile test results for the multi-material printing experiment are shown in Figure 27. Unlike the noticeable difference between the tensile strength values of pure ABS and PLA, the multi-material printed sample did not show much difference when variance was taken into account.
We observed the fracture part of the multi-material specimen through the optical microscope to analyze the results. Many cases of breakage are found, especially at the interface of the two materials in multi-material printed specimens. These defects are caused by printer or operator error, resulting in a weakening of the tensile strength.
Another reason why such void and overlap phenomena are present may be due to the characteristics of the FDM printing method. A general-purpose FDM printer prints the edges of the target first, as shown in Figure 29, followed by filling in the inner sides.
Experiment for Structure Effect of Dual Materials
The difference in tensile strength depending on the structural design of the specimen is shown in Figure 32. Interestingly, even if the material proportion of each specimen was kept at 50%-50%, the tensile strength shows a relatively large difference depending on the design of the structural arrangement. Considering that the 3-line and 4-line type samples tested for the experiment do not show much difference in the ultimate tensile strength, we can conclude that one additional line does not have much influence on the overall strength of the sample.
However, the pattern shows increased tensile strength as the layer in the type 3 stripe pattern is split into two vertical layers, creating a type 6 stripe. The same applies to a 4-line type instance that is split into an 8-line type instance. To analyze the reasons for the increase in tensile strength despite the same horizontal structural arrangement, we observed the structure of the preparation with an optical microscope.
On the other hand, the planes between the two materials in Figure 33 (a) and (b) show better contact compared to those in Figure 33 (c). Therefore, even if the same proportion is used for a multi-material FDM 3D printing, the tensile strength shows a large variation depending on the structural arrangement.
Mixing of Composite Material by Twin Screw Extruder
Experimental Setup
Carbon Materials Based Thermoplastic Filament
Acrylonitrile butadiene styrene (ABS) is a widely used thermoplastic polymer. it is amorphous and has no true melting point. It is also a terpolymer made by polymerizing styrene and acrylonitrile in the presence of polybutadiene. When mixing polymers, the solubility parameter is used to measure the solubility of polymers [27].
Since the solubility of epoxy resin, carbon fiber and ABS is almost the same, it is expected that interaction between them will be very good. If the filament is created with this positive aspect, the filament will be well aligned as shown on the left side of Figure 37.
![Table 8. The solubility parameter ([28], [29])](https://thumb-ap.123doks.com/thumbv2/123dokinfo/10522665.0/44.892.108.774.565.709/table-8-the-solubility-parameter-28-29.webp)
Results
Conclusion
Objectives
Estimation of Ultimate Tensile Strength
Polynomial Regression
The goal of regression analysis is to model the expected value of the dependent variable y with respect to the value of the independent variable (or vector of independent variables) x. Simple linear regression uses the model y01x, where is an unobserved random error with mean zero conditional on the scalar variable x. In this model, for each unit increase in the value of x, the conditional expectation of y increases by 1 unit.
In general, the expected value of y can be modeled as an nth-degree polynomial, yielding a general polynomial regression model as Equation (2). Conveniently, all of these models are linear in estimation, since the regression function is linear with respect to the unknown parameters 0, 1,. Therefore, in least squares analysis, the calculation and inference problems of polynomial regression can be completely handled by multiple regression techniques.
RBF Regression
GP Regression
The signal variance and the noise variance are coded with the parameters 2f and n2, and l codes the length scale of the process. It gives uncertainty about the estimate (one standard deviation) and smoothed number, which is an intuitively acceptable result.
Mechanical Properties Assessment Using Finite Element Reliability Analysis
- FERUM(Finite Element Reliability Using Matlab)
- Reliability Analysis
- Experimental Data
- Results
If the random variable space is transformed into the standard random variable space, the failure probability Pf can be rewritten as Equation (8). In the FORM, the limit state function G(u) is approximated by a linear function at the point u* defined by Equation (9) to obtain the failure probability Pf. The following table 11 shows a total of 60 results obtained from the 12 samples tested for each of the five.
The reference point was set at 30 MPa to obtain the probability that the printed sample has the ultimate tensile strength above a certain stress. The FERUM is run twelve times to derive the probability that the ultimate tensile strength of the pressed sample will be greater than 30 MPa. The [112] type specimen has a failure probability of 1, which actually has a tensile strength of nearly 40 MPa.
The results of the remaining psalms also give convincing results when compared to the actual data. The results of the tensile test were used for the FORM tensile strength analysis, in which the probability of failure was estimated.
Conclusion
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