Fereidoon Delfanian

Failure Analysis and Mechanical Characterization of 3D Printed ABS With Respect to Layer Thickness and Orientation

In contrast to conventional subtractive manufacturing methods which involve removing material to reach the desired shape, additive manufacturing is the technology of making objects directly from a computer-aided design model by adding a layer of material at a time. In this study, a comprehensive effort was undertaken to represent the strength of a 3D printed object as a function of layer thickness by investigating the correlation between the mechanical properties of parts manufactured out of acrylonitrile butadiene styrene (ABS) using fused deposition modeling and layer thickness and orientation. Furthermore, a case study on a typical support frame is done to generalize the findings of the extensive experimental work done on tensile samples. Finally, fractography was performed on tensile samples via a scanning digital microscope to determine the effects of layer thickness on failure modes. Statistical analyses proved that layer thickness and raster orientation have significant effect on the mechanical properties. Tensile test results showed that samples printed with 0.2 mm layer thickness exhibit higher elastic modulus and ultimate strength compared with 0.4 mm layer thickness. These results have direct influence on decision making and future use of 3D printing and functional load bearing parts.

Fiber bias effect on characterization of carbon fiber-reinforced polymer composites by nanoindentation testing and modeling

Fiber bias effect on characterization of carbon fiber-reinforced polymer composites by nanoindentation testing has been investigated by computer modeling and validated by experiments. IM7/PEEK composite was selected as a case study material. Nanoindentation tests using Berkovich indenter were carried out on fiber longitudinal direction and in the near fiber region of the matrix to attempt to determine the nanomechanical properties of the fibers and the interphase. A 3D finite element analysis model for simulating nanoindentation was developed, taking into account the carbon fibers’ transversely isotropic properties. A fiber bias effect inducing a gradient in modulus in fiber–matrix interphase region was observed from tests and confirmed by modeling, and this property transition thickness induced by the fiber bias is about 1–2 µm depending on the indentation depth, which suggests an inherent difficulty when attempting to determine the true interphase properties experimentally using the nanoindentation testing.

Estimating the Effect of Helium and Nitrogen Mixing on Deposition Efficiency in Cold Spray

Cold spray is a developing technology that is increasingly finding applications for coating of similar and dissimilar metals, repairing geometric tolerance defects to extend expensive part life and additive manufacturing across a variety of industries. Expensive helium is used to accelerate the particles to higher velocities in order to achieve the highest deposit strengths and to spray hard-to-deposit materials. Minimal information is available in the literature studying the effects of He-N2 mixing on coating deposition efficiency, and how He can potentially be conserved by gas mixing. In this study, a one-dimensional simulation method is presented for estimating the deposition efficiency of aluminum coatings, where He-N2 mixture ratios are varied. The simulation estimations are experimentally validated through velocity measurements and single particle impact tests for Al6061.

Phased Array Ultrasonic Technique Parametric Evaluation for Composite Materials

A series of ultrasonic elements arranged in a phased array transducer can provide the capability to activate each element separately but in a programmed sequence. This will help the acoustic signal to be generated at desired focusing distances and anticipated angles for specific materials and structures. In case of composite material inspection, this characteristic of the phased array method can improve the undesirable effects of the high attenuation and anisotropic structure of composite materials on response signals. In this study different phased array probes and wedges which are commercially available were evaluated for their response signals’ characteristics. First, the capability and resolution of bulk wave generation were studied for each set of probe and wedge, and the response signals were compared to that of the conventional single element ultrasonic transducers for different thicknesses composite plates. Then the resolution of the response signals and their sensitivity to defect size were evaluated and compared to the single element transducers as well. Next, each phased array probe and wedge set was used to generate plate waves in aluminum plates based on plate wave propagation theory, probe and wedge physical properties and the definition of delay law. Results show a general improvement in response signals’ strength and resolution for phased array method in comparison to the single element transducers. Also some plate wave modes could be generated with optimized signal generation parameters in phased array system.Copyright

Ultrasonic phased array techniques for composite material evaluation

The increasing rate of composite materials usage in the industries and researches implies finding the suitable method for testing and evaluation of composite materials. The composites are susceptible to flaws during production and the inspection costs suggest the use of NDT methods. Non-destructive testing is an appropriate method to detect the flaws and anomalies in the materials, however, due to an-isotropic structure of the composite materials, it is required to modify the techniques to find the most appropriate and accurate process for detecting flaws and anomalies in composite materials. The objective of this paper is to evaluate the feasibility and accuracy of nondestructive testing methods with emphasis on ultrasonic phased array technique for the integrity and structural evaluation of composite materials. In this approach three different composite samples were used for testing including one carbon fiber and two glass fiber samples. ultrasound phased array technique evaluated to perform the testing...

Investigating the Structural Properties of Corn Stover Biomass

The purpose of this study is to analyze structural material properties of biomass materials, namely corn stover. The microstructure of the biomass is examined by using a nano-hardness testing machine (NANOVEA®). The goal of this analysis is to test the hardness and elasticity of individual fibers using nanoindentation and to develop testing techniques to perform this task. The results of the stated tests are statistically analyzed. The measured structural properties of the biomass have the potential to be used in computer simulations for structural analysis and bulk solid flows. The bulk fluid motion of the pulverized/chopped biomass can be simulated in storage and transportation equipment, including auguring screws and pneumatic conveyance systems, as well as devices for feeding biomass feedstocks in biorefineries. Traditional biochemical and thermochemical reactors operate as batch systems because of the difficulty of feeding the biomass feedstock in a continuous manner. Having a clearer background about the structural and rheological properties of biomass feedstock will help simulate and design the bulk-solid flows within storage bins and conveyance systems.Copyright

EVALUATING THE MECHANICAL PROPERTIES OF CARBON FIBER REINFORCED POLYMER MATRIX COMPOSITE MATERIALS AT ROOM AND ELEVATED TEMPERATURES

A series of tensile, compression and shear tests in room temperature were carried out on carbon fiber reinforced polymer matrix composite materials (IM7/PEEKEK) to evaluate their mechanical properties. Also tensile tests at 160 degrees Fahrenheit (72 degrees Celsius) in longitudinal and transverse directions were done to study the effects of such temperature on the tensile strength of the mentioned composite materials. The setup of the testing equipment and the furnace that was used to provide elevated temperature conditions limited the possibility of conducting compressive and shear tests at high temperature as well as raising the temperature to higher levels. The experiments were set up in accordance with ASTM standards that best corresponded to the test specifications. Specimens were categorized into groups according to their nature of testing. All the specimens were reinforced at both ends by means of tabs which were bonded on both faces to reduce the effects of the external pressure exerted on them through the grips of the testing machines and were tested until failure. Load, elongation (displacement) and strain data were recorded by means of strain gages and data acquisition systems.The accuracy of the experimental data for the room temperature portion of the experiments is verified by comparing them to those of the most equivalent composite family, as having not been given any information regarding the structural properties and manufacturing processes of the composite materials that were used throughout the experiments made it difficult to find exact ASTM standards and reference materials for the testing and comparison of results.The results of the experiments showed that the tensile strength of this particular composite material is not effected by the 160 degrees Fahrenheit temperature; a point that is proved by the literature indicating their specific and sensitive application in aircraft heat dissipation [1].Copyright

Experimental Verification of Model Pressurized Thick-Walled Cylinder With Numerical and Theoretical Methods

Pressurized thick-walled cylinders undergo repeated cycles of high stress and temperatures that may severely shorten the life of the component. Testing pressurized cylinder can help to evaluate the strength of the cylinder. This research seeks to determine the pressure to which the component is subjected by instrumenting the outside of the cylinder, and to evaluate hoop strain and hoop stress of the internal and external surface of the pressurized thick-walled cylinder. This study provides experimental results and then compares them with theoretical and numerical data for the cylinder under investigation. Using the experimental method, an axial load up to 15,000 lb is applied to the cylinder using a Landmark 370 MTS unit to generate pressure inside the cylinder wall. Lame equations are used to calculate hoop stress theoretically. The numerical data is obtained using finite element simulation (ANSYS) to calculate hoop stress and hoop strain at the internal and external surfaces of the cylinder. This work provides useful information for evaluating the strength of thick-walled cylindrical structures in a laboratory setting.Copyright

Interface Integrity Evaluation of Explosively Welded Metallic Structures

Explosively bonded tubes have been applied in high pressure and high temperature environments, such structures are usually consisting of dissimilar metals which are very difficult to be welded together by other conventional welding methods. In this study, various experimental techniques were used for the evaluation of interface integrity between steel major tube and tantalum donor tube. First, X-ray diffraction technique was used to profile the residual stress levels in the tantalum donor tube before bonding and steel major tube after bonding, especially the hoop stress level which is critical to quality control. Also, other experimental techniques including digital microscopy for interface geometrical features, X-ray fluorescence spectroscopy for interface compositions, and nano-hardness testing for materials strength at micro/nano scale were further applied to explain bonding mechanisms and to quantify bonding interface conditions. Then nondestructive ultrasound C-scan technique was used to create acoustic images of the bonding interfaces and the results showed that the technique has the potential to find weak interface and to further quantify good and poor bonds. Finally, destructive testing techniques were used to measure the interface shear and tensile strength and to study the interface failure mechanisms, and the results agree well with other experimental techniques.Copyright

Ultrasound Characterization of IM7/PEEK Composite Materials

IM7/PEEK composite materials may experience large mechanical and thermal stresses during service, and their failure mechanisms can be complex and have various modes. In this study, IM7/PEEK specimens for interlaminar shear strength testing were evaluated by both nondestructive ultrasound method and standard destructive test. First, IM7/PEEK specimens were fabricated under various processing parameters including roller speed, torch temperature, roller temperature, compaction level, N2 flow rate, and material tension level. Then ultrasound longitudinal wave velocity that is normal to fiber direction was evaluated and the influence of measuring locations and ultrasound frequencies from 0.5 MHz to 10.0 MHz were studied. Experimental results showed that 5.0 MHz is the most sensitive frequency to fabrication conditions and that ultrasound velocity can be related to some processing parameters such as materials tension, N2 flow rate and temperature. Finally, interlaminar shear strength experiments were carried out by standard short beam bending destructive tests. The relationship between ultrasound velocity and standard destructive tests were analyzed and the potential of ultrasound velocity for interlaminar shear strength evaluation was discussed.Copyright