Mechanical Characterizations of 3D-printed PLLA/Steel Particle Composites

The objective of this study is to characterize the micromechanical properties of poly-L-lactic acid (PLLA) composites reinforced by grade 420 stainless steel (SS) particles with a specific focus on the interphase properties. The specimens were manufactured using 3D printing techniques due to its many benefits, including high accuracy, cost effectiveness and customized geometry. The adopted fused filament fabrication resulted in a thin interphase layer with an average thickness of 3 μm. The mechanical properties of each phase, as well as the interphase, were characterized by nanoindentation tests. The effect of matrix degradation, i.e., imperfect bonding, on the elastic modulus of the composite was further examined by a representative volume element (RVE) model. The results showed that the interphase layer provided a smooth transition of elastic modulus from steel particles to the polymeric matrix. A 10% volume fraction of steel particles could enhance the elastic modulus of PLLA polymer by 31%. In addition, steel particles took 37% to 59% of the applied load with respect to the particle volume fraction. We found that degradation of the interphase reduced the elastic modulus of the composite by 70% and 7% under tensile and compressive loads, respectively. The shear modulus of the composite with 10% particles decreased by 36%, i.e., lower than pure PLLA, when debonding occurred

Glocal integrity in 420 stainless steel by asynchronous laser processing

Cold working individual layers during additive manufacturing (AM) by mechanical surface treatments, such as peening, effectively “prints” an aggregate surface integrity that is referred to as a glocal (i.e., local with global implications) integrity. Printing a complex, pre-designed glocal integrity throughout the build volume is a feasible approach to improve functional performance while mitigating distortion. However, coupling peening with AM introduces new manufacturing challenges, namely thermal cancellation, whereby heat relaxes favorable residual stresses and work hardening when printing on a peened layer. Thus, this work investigates glocal integrity formation from cyclically coupling LENS® with laser peening on 420 stainless steel

Potential of natural rubber latex in cement mortar for thermal insulating material in buildings

The improvement of cement mortar’s thermal and mechanical properties has been greatly impacted by the addition of polymeric materials. However, polymers added to mortar shouldn’t impair either its mechanical or thermal conductivity properties. The main idea of this project is to insulate buildings by reinforcing their constituent mix with natural rubber latex (NRL) to reduce thermal conductance from excessive solar radiation which causes discomfort to building occupants. Consequently, this study presents experimental findings on the influence of natural rubber latex (NRL) on the properties of NRL-modified mortar. Five varying percentages of NRL (0.5%, 1.0%, 1.5%, 2.0% and 2.5%) were added into the mortar. Properties such as thermal conductivity, water absorption capacity, compressive and flexural strengths were evaluated. In addition, scanning electron microscopy was employed for the microstructural investigation. The experimental findings demonstrated that adding 2.5% NRL to mortar increased its thermal conductivity of mortar significantly thus enhancing its insulative properties. Even though adding NRL to mortar decreased the compressive and flexural strengths of some mixes, this wasn’t too substantial nor substandard. The tests that were executed demonstrate that the NRL has a huge potential to insulate cement mortar

Dynamic Mechanical Behavior from Hybrid Additive Manufacturing

The overarching objective of this research was to investigate the dynamic mechanical behavior from an enabling surface treatment technology employed during additive manufacturing (AM) to print functional 3D mechanical properties layer-by-layer. More specifically, this study combined peening with additive manufacturing to print favorable 3D mechanical properties, such as compressive residual stress and work hardening, in preferential layer intervals throughout the entire build volume. The effects of coupling printing and peening were examined for both metal and polymer material systems. For metals, the dynamic mechanical behavior was assessed by Split-Hopkinson Pressure Bar. For polymers, the dynamic mechanical behavior was assessed by low velocity impact and by dynamic mechanical analysis. The metal of interests was 420 stainless steel. The polymer of interest was arylonitrile butadiene styrene (ABS). ABS was tested by drop tower impact and Charpy tests to examine the energy absorption and fracture strength. The additive processes for 420 stainless steel and ABS were laser engineered net shaping (LENS®) and fused filament fabrication (FFF), respectively. The peening processes for 420 stainless steel and ABS were laser peening (LP) and shot peening (SP), respectively. Printing consistently superior mechanical properties in metals is an essential but currently difficult aspect of AM that often results in poor strength, fatigue, and corrosion performance. Substandard mechanical properties and poor performance is the critical technical barrier to more widespread adoption of AM technology. Current 3D metal printers lack the capability to enhance mechanical properties while printing a part. Apart from fine-tuning a print recipe, there is currently no in-situ method to improve the properties throughout the build. A hybrid approach that cyclically couples additive manufacturing with peening is a new and untested method to improve performance of complex geometries not possible by traditional manufacturing; by enabling functionally gradient mechanical properties throughout the entire build volume. Results indicated that hybrid-AM was capable imparting a unique structural integrity throughout the entire build volume. Favorable mechanical properties were not completely cancelled from the thermal loads of printing on a previously peened layer. An optimum layer peening frequency was found to exist that favorably enhanced static and dynamic mechanical properties. The study also showed a dependence of the dynamic mechanical behavior on the hybrid processing conditions, namely layer peening frequency. Results showed that the ability to absorb and dissipate energy was influenced by coupling printing and peening

Ultrasonic Mapping of Hybrid Additively Manufactured 420 Stainless Steel

Metal hybrid additive manufacturing (AM) processes are suitable to create complex structures that advance engineering performance. Hybrid AM can be used to create functionally graded materials for which the variation in microstructure and material properties across the domain is created through a synergized combination of fully coupled manufacturing processes and/or energy sources. This expansion in the engineering design and manufacturing spaces presents challenges for nondestructive evaluation, including the assessment of the sensitivity of nondestructive measurements to functional gradients. To address this problem, linear ultrasound measurements are used to interrogate 420 stainless steel coupons from three manufacturing methods: wrought, AM, and hybrid AM (directed energy deposition + laser peening). Wave speed, attenuation, and diffuse backscatter results are compared with microhardness measurements along the build/axial direction of the coupons, while microstructure images are used for qualitative verification. The ultrasound measurements compare well with the destructive measurements without any substantial loss in resolution. Furthermore, ultrasonic methods are shown to be effective for identification of the gradient and cyclic nature of the elastic properties and microstructure on the hybrid AM coupon. These results highlight the potential of ultrasound as an efficient and accessible nondestructive characterization method for hybrid AM samples and inform further nondestructive evaluation decisions in AM

Glocal integrity in 420 stainless steel by asynchronous laser processing

Cold working individual layers during additive manufacturing (AM) by mechanical surface treatments, such as peening, effectively “prints” an aggregate surface integrity that is referred to as a glocal (i.e., local with global implications) integrity. Printing a complex, pre-designed glocal integrity throughout the build volume is a feasible approach to improve functional performance while mitigating distortion. However, coupling peening with AM introduces new manufacturing challenges, namely thermal cancellation, whereby heat relaxes favorable residual stresses and work hardening when printing on a peened layer. Thus, this work investigates glocal integrity formation from cyclically coupling LENS® with laser peening on 420 stainless steel

Electric Resistance Sintering of Al-TiO₂-Gr Hybrid Composites and Its Characterization

In the present work, Al-TiO2-Gr hybrid composites were fabricated through a sustainable manufacturing approach, i.e., ERS (Electric Resistance Sintering) technique. In this experimental work, sintering is performed in a high-density graphite die, which also works as a heating element. The green compacts kept in the graphite die are sintered in two ways simultaneously (conduction and resistance heating). This facilitated the accomplishment of the sintering at a lower current (300–500 A). The aluminum (Al) was reinforced with 9 wt. % TiO2 (rutile) nanoparticles and 3 wt. % graphite microparticles to synthesize a self-lubricated high wear resistance material. Mechanical properties such as density, hardness, and wear loss of the Al-TiO2-Gr hybrid composite were investigated. Scanning electron microscopy (SEM), Energy-dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD) were performed for microstructural investigation. The experiments were performed according to the Taguchi design of the experiment, where three input process parameters (temperature, holding time, and sintering load) were taken to fabricate the Al-TiO2-Gr composite. The sintering temperature of 550 °C resulted in the maximum value of mean sintered density (approx. 2.45 gm/cm3). The holding time of 10 min for the sintering resulted in the maximum value of mean sintered density and mean hardness (HRB 53.5). The mean value of wear loss was found to be minimum for the composites sintered at 600 °C for 10 min. The maximum value of the sintering load (800 N) revealed better density and hardness. Worn surfaces and wear debris were also analyzed with the help of SEM images. The sintering temperature of 600 °C resulted in imparting more wear resistance which was proved by smooth surfaces, micro-cutting, and fewer crates, grooves, and smaller pits

Low velocity impact of ABS after shot peening predefined layers during additive manufacturing

International audienc

Low velocity impact of ABS after shot peening predefined layers during additive manufacturing

International audienc