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Nickel-titanium (NiTi) shape memory alloys (SMAs) undergo phase transformation between austenitic and martensitic phases in response to applied thermal or mechanical stress, resulting in unique properties and applications. However, machinability often becomes challenging due to property and temperature sensitivity attributes. The use of chilled air to influence machinability in macro-milling was investigated in this study. Other than that, differential scanning calorimetry (DSC) was used to determine the temperature of phase transformation. The results showed that milling with chilled air and minimal lubrication significantly improved machining performance by reducing tool wear and burr formation. Moreover, surface quality has also improved significantly. A notable discovery is that the machining process can change the critical conditions for phase transition, enabling new performance capability of tuning material hysteresis. [ABSTRACT FROM AUTHOR]

This study suggests reverse compensation as a method to secure the dimensional stability of automotive parts manufactured using carbon fiber-sheet molding compound (CF-SMC), even after molding. After completion of molding, the uncured material undergoes shrinkage during curing, resulting in distortion of the dimensions. At this stage, the dimensions can be corrected by suppressing the distortion caused by shrinkage. This method can reduce the cost and time required for development. To evaluate the degree and condition of shrinkage of the material during curing, the shrinkage rate was measured using a dilatometer, and the curing behavior during product molding was examined by differential scanning calorimetry (DSC). After molding, the temperature change of the demolded product was inspected, and the glass transition temperature (Tg) of the product was evaluated using dynamic mechanical analysis (DMA) to confirm that reverse compensation was possible within a certain amount of time, even for thermoset products. To examine the possibility of reverse compensation, the material properties were measured and used as input data for finite element method (FEM), in which the degree of distortion was observed after free cooling and after using reverse compensation cooling. To confirm the actual performance, a jig for reverse compensation was manufactured, and reverse compensation was performed immediately after molding. The flush values were measured after seven days, considering the possible dimensional regression caused by residual stresses. The results confirm the possibility of reverse compensation because the thermosetting product can reach temperatures higher than the mold temperature during molding owing to heat generation by curing and can maintain its temperature above the onset of Tg for a certain period of time after demolding. Therefore, the dimensional quality can be improved by manufacturing an appropriate jig. [ABSTRACT FROM AUTHOR]

Fused filament fabrication (FFF) is an additive manufacturing (AM) technology which is rapidly progressing from production of prototypes to manufacture of customized end use parts for the automotive, biomedical, and aerospace industries. The properties of manufactured parts have been proven to be dependent on not only the material's inherent properties but importantly the FFF process parameters. Commodity thermoplastics such as acrylonitrile butadiene styrene (ABS) and polylactic acid (PLA) have been on the forefront of FFF research since its development. However, as FFF technology progresses from rapid prototyping to rapid manufacturing, understanding the behaviour of high-performance engineering thermoplastics in this process is imperative. While previous studies have investigated the effects of FFF process parameters on polyether ether ketone (PEEK) and polyetherimide (PEI), more limited research has been performed on polyether ketone ketone (PEKK) despite its widespread applications in the biomedical and aerospace industries. This study investigated the effects of process parameters including build orientation, infill pattern, number of contours and raster angle on the tensile properties of PEKK. Tensile test results showed significant variations in Young's modulus and elongation at break. Statistical analysis was performed which determined the optimum process parameters to maximize tensile properties and revealed that build orientation was the most significant parameter, followed by number of contours. Fractography showed differences in failure mode and ductility among the sample groups. Analysis using differential scanning calorimetry (DSC) showed that the difference in percentage crystallinity among sample groups was not significant and thus the varied tensile properties was improbable to be due to differences in crystallinity developed within the specimens. Further analysis revealed that a variation in FFF process parameters can cause differences in percentage, size and location of porosity which in turn affects mechanical properties. [ABSTRACT FROM AUTHOR]

This research investigates the process behaviour by prediction of the pull force required to drag the raw materials through heated die at different reinforcing material configuration during pultrusion. Pultrusion is a continuous manufacturing process that is widely used in manufacture for composite profiles. A specially designed device, friction force by virtue of pulling on 'resin impregnated' fibres with both liquid resin and partially cured resin, was employed to measure pulling force against temperature and resin conversion. This allowed to experimentally simulate materials tracing in short and long die length used in process. Differential scanning calorimetry (DSC) was used to determining polymer conversion. The results shows that the downstream part of a die has no significant effect on the pulling force before a specific conversion level is achieved and that higher resin conversion leads to a higher friction at viscous/liquid zone. The difference noted is much more significant when the temperature is low (e.g. room temperature) and considerably drops due to on rising temperature. Further, a new mathematical model is proposed that predicts the rise in compaction pressure on increasing fibre volume fraction and drag velocity which is an opposite characteristic to tapping angle and part thickness considerations. Similarly, many parameters including shrinkage, viscous force and dry friction were modelled and simulated for ortho polyester resins as a function of temperature and resin conversion during dynamic pulling. The study has direct application in configuring pultrusion manufacturing customisation for a specific configured material, components manufacturing and respective designing of the die for the profile to be manufactured. [ABSTRACT FROM AUTHOR]

Manufacturing thermoplastic composites (TPCs) with excellent mechanical properties require advanced methods with reduced costs and better overall efficiencies. In this study, fiber-reinforced thermoplastic polymer composite laminates were manufactured using an automated fiber placement (AFP) manufacturing technology. The effects of processing temperature (from 320 to 500 ℃), lay-up speed (from 20 to 260 mm/s), consolidation force (from 100 to 600 N), and prepreg tape tension (from 0 to 9 N) on the quality of the resulting laminates manufactured using the laser AFP system were investigated. The interlayer bond strength was characterized using wedge peel tests on samples prepared with different process parameters. The studies were complemented by measurements of the thermal properties of the composites using differential scanning calorimetry. The optimized process parameter windows were determined to be 360 to 400 ℃ for the irradiation temperature, 140 to 160 mm/s for the lay-up speed, 100 N for the consolidation force, and 3 to 5 N for the prepreg tape tension, respectively. The microscopic analysis of the sample cross-sections and peel-damaged surfaces revealed that the different distributions of the resin matrix resulting from the different processing parameters affected the interlayer strength. These results may provide an important reference for manufacturing TPC used in aerospace, defense, and automotive applications. [ABSTRACT FROM AUTHOR]

This paper aims to investigate the high-speed machinability and phase transformation behavior of nickel-titanium shape memory alloys considering the process and post-process perspective. The tool wear results showed that PCD tool has great potential over carbide considering the limitation of quick tool wear in the high cutting speed range. Maximum tool life was achieved at the cutting speed of 130 m/min. The results obtained from differential scanning calorimetry indicated that the latent heats and transformation temperatures of nickel-titanium shape memory alloy are highly cutting speed dependent. Decrease of the cutting speed resulted in increased impair on these properties. It was found that the decrease of the cutting speed causes a decrease in the transformation enthalpy. The results revealed that increased transformation hysteresis is highly cutting speed related. Two hundred fifty m/min and 70 m/min cutting speed values resulted in 31.5 and 37.8 °C post-machining transformation hysteresis respectively. Compared to the unmachined sample, a minimal change in functional properties was achieved at the cutting speed of 250 m/min. Likewise, the lowest cutting speed (70 m/min) led to maximum subsurface hardening and deeper machining-induced layer according to metallurgical investigations. Residual austenite formation was evident on the subsurface of the machined specimens. [ABSTRACT FROM AUTHOR]

Fused filament fabrication (FFF) is a widely used extrusion-based additive manufacturing process due to its low operating cost and available material options. Polylactic acid (PLA) is a bio-based compostable polymer extensively used as a feedstock material in FFF. The application of PLA in engineering and medical applications is limited due to the low thermal stability associated with the polymer. The present work aims to study the effect of thermal annealing on FFF-printed PLA in static and dynamic flexural loading. Response surface methodology (RSM) is chosen as a design of experiment method to study the effect of annealing time and temperature on flexural properties of printed PLA. Annealing is found to be advantageous in increasing the dynamic flexural properties. Improved glass transition temperature, stiffness, thermal stability, and crystallinity are also evident with annealing. However, annealing is found to be detrimental in improving static flexural properties. Considering the desirability function (DF) approach, annealing time and temperature are optimised for measured static and dynamic flexural properties. Samples are further investigated in scanning electron microscope for failure mode and differential scanning calorimetry for crystalline behaviour of annealed PLA. Empirical models are proposed for predicting the flexural behaviour of printed PLA. The current study has shown that the FFF-printed PLA can be tailored to specific application requirements due to its stable characteristics for thermal loading with thermal annealing. [ABSTRACT FROM AUTHOR]

The Ti9Nb1, Ti8.5Nb1.5, Ti8Nb2 and Ti7.5Nb2.5 alloys were developed by powder mixing, compaction and sintering followed by heat treatment. Phase transformation on the sintered and heat-treated Ti (10–25 wt.%) Nb alloys were investigated using the X-ray diffraction (XRD) and differential scanning calorimetry (DSC). The DSC analysis shows an endothermic peak at ~ 800 °C in Ti9Nb1 alloy. For Ti8.5Nb1.5 and Ti8Nb2 alloys, both endothermic peaks appeared with a slight variation ~ 660 °C while the Ti7.5Nb2.5 alloy occurred at 490 °C. All these endothermic peaks were reversible upon cooling and revealed exothermic peaks which confirm the α ↔ β phase transformation. These Ti–Nb alloys were all subject to heat treatment at 1100 °C (β-zone). The FCC Ti–Nb phase was detected by the XRD analysis in as-sintered Ti7.5Nb2.5 alloy. Moreover, a BCC phase coexisted with the HCP in Ti9Nb1, Ti8.5Nb1.5 and Ti8Nb2 alloys. Optical microscopy analysis revealed the equiaxed grains composed of the light β-phase segregating on the grain boundaries. The Ti9Nb1 has low Vickers hardness of all alloys while Ti8Nb2 and Ti7.5Nb2.5 alloys are harder due to high amount of Nb content. The EDS and Eltra techniques confirmed the chemical compositions and O contents. Generally, the densities of the Ti–Nb alloys increased with increasing Nb content. [ABSTRACT FROM AUTHOR]

Effect of size and shape of the additively manufactured Nickel-Titanium (NiTi) alloys on their thermomechanical properties is experimentally studied. Although additive manufacturing is shown as a solution to the difficulties of machining of NiTi shape memory alloys (SMAs), our understanding of the effect of various processing (e.g., laser power, scanning pattern, etc.) and part characteristics (e.g., part geometry) on the resulting properties is not complete. During the SLM fabrication process, various factors influence the properties of the final product. In this study, we investigated the effect of size and shape of the SLM samples on the thermomechanical behavior of the parts. Tensile specimens with different thicknesses and shapes were fabricated for this investigation. The accuracy of fabrication is discussed for all of the specimens. Differential scanning calorimetry (DSC) measurements were conducted to compare the transformation temperatures of specimens with different size and shape. Moreover, tensile tests including loading, unloading, and heating were done for all of the specimens and the mechanical responses were compared with each other. Digital image correlation (DIC) was used for strain measurements as a more accurate strain measurement tool. The transformation temperatures of the fabricated parts were similar for parts with different shapes and sizes. From the mechanical tests, higher strength was observed for the thinner parts in both rectangular and oval specimens. Also, from the mechanical behavior of different shapes, it was observed that the rectangular showed higher critical stress than their equivalent oval specimens. [ABSTRACT FROM AUTHOR]

One of the major concerns when using prepreg materials for advanced composite manufacturing is the cure advancement. Although this type of prepreg curing is usually programmed to occur at high temperatures, the exposition to environmental conditions during processing, intrinsic to the industrial production, leads to the cure advancement and, consequently, to the detriment of prepreg's processability. Therefore, techniques that provide accurate, relatively low-cost, and fast alternatives for tracking prepreg out-time are of great interest for composite industries. In this scenario, the present work aims to provide information on the use of thermal and rheological characterization techniques for monitoring the prepreg out-time. To do so, prepreg specimens were aged for pre-established periods (0 to 60 days) and characterized by differential scanning calorimetry (DSC) and dynamic shear rheometry techniques. Also, laminates were manufactured from aged prepregs, and their properties were characterized by ultrasound and volume fraction analyses and by interlaminar shear strength (ILSS) tests. The combination of the findings provides out-time tracking and properties monitoring alternatives for industries and points out to the possibility of extending prepreg out-time limits, reducing the waste on prepreg processing, one of the main challenges associated with composite manufacturing. [ABSTRACT FROM AUTHOR]

During the fabrication of composite parts, the residual stresses build up causing the shape distortion in laminated composites and deteriorate its mechanical performance. In the case of angled/cylindrical parts, the stress leads to the change in the encircled angle. The effect of adding nano/microparticles on the mechanical properties has been the focus of many researchers in the recent past, but their effect on the process induced shape distortion of composite parts has been studied rarely. This study investigates the effect of silica particles on shape distortion in glass/unsaturated polyester cross-ply C-shaped composite parts having an enclosed angle of 240°. Composite parts were fabricated with a varying fraction of silica particles (0, 3, 5, and 7% by weight of resin). In order to analyze curing behavior, thermal kinetics of the resin system was investigated using differential scanning calorimetry (DSC). The experimental results showed that the value of diameter reduction was reduced from 6 mm to 3 mm by addition of 5% silica particles. Furthermore, composite part distortion was predicted using an analytical model and compared with experimental results for validation. [ABSTRACT FROM AUTHOR]

This study focuses on the development of a process-based simulation model coupled with differential scanning calorimetry (DSC) and dynamic mechanical analyzer (DMA) experiments. The cure kinetics and rheology of an epoxy-amine resin were characterized in order to predict the degree of cure and viscosity behavior in an out-of-autoclave (OOA) process condition. Both phenomenological reactions and chemo-rheological models were applied to effectively predict the degree of cure and resin viscosity. Using these results, it is possible to predict the minimum viscosity, gelation, and vitrification, which are the main process factors of the multi-stepped cure cycles, and reduce the number of process trials. It was found that there was a good correlation between the experimental results and model predictions under isothermal and non-isothermal temperature profiles. Furthermore, this study demonstrates that there is an additional scope for optimization in the conventional cure cycles recommended by prepreg manufacturers, especially when a low viscous state is required. The optimized cure cycle led to a substantially high fiber fraction (58.96 vol%) and a low void content (0.15 vol%), as compared to the conventional cure cycles. [ABSTRACT FROM AUTHOR]

Shape memory alloys (SMAs) provide an attractive solid-state actuation alternative to engineers in various fields due to their ability to exhibit recoverable deformations while under substantial loads. This feature is of particular importance when utilising the smart composite materials reinforced by SMA. Many constitutive models describing this repeatable phenomenon have been proposed, where some models also capture the effects of rate-independent irrecoverable deformations in SMAs. This paper presents experimental investigations and numerical simulations on shape memory alloys. First, by consisting in determining the transformations of equiatomic Ti-Ni shape memory alloys by differential scanning calorimeter. Then, in order to validate a 3D numerical model of the pseudoelastic behaviour of SMA allowing a finite strain analysis, a set of experimental tests at various initial temperatures is proposed. Finally, the numerical simulations of uniaxial tests performed on shape memory alloys are presented and compared with experimental data, permitting the validation of the proposed modelling. Reasonably good correlation is obtained between the experimental and model predictions. [ABSTRACT FROM AUTHOR]

The morphology evolution of thermoplastics made by micro-injection molding (μIM) in a uniform miniaturization manner has not been documented yet. In the present study, the crystal morphologies within μIM high-density polyethylene parts were investigated with the aid of rheology measurement, polarizing optical microscopy, scanning electron microscopy, and differential scanning calorimetry. It was discovered that unlike conventional injection molded parts with spherulites predominating, uniformly miniaturized products have highly oriented lamellae starting to appear in the skin layer. For 175-μm-thick μIM parts (M175), interlocking shish–kebab structures exist throughout the thickness. Furthermore, the origins of different crystal morphologies with various part thicknesses were discussed mainly from the viewpoints of rheology and thermodynamics. It was revealed that the flow-induced crystallization is one of the key factors responsible for the unique super structures. More quantitatively, there is a critical shear rate of 3.0 × 10 5 s −1 existing for forming highly oriented molecular structures. Meanwhile, on the basis of the model from the literature, an elongational rate as high as 4.4 × 10 4 s −1 was also identified at the channel center for M175. [ABSTRACT FROM AUTHOR]