Key Engineering Materials Vol. 751

Abstract: This paper proposes a new joining approach for dissimilar materials, called ‘the fastenerless-riveting,’ employing the friction stir forming (FSF). The FSF is a friction stir process invented by Nishihara in 2002. In FSF, a substrate material was put on a die firstly. Next, friction stirring was conducted on the back surface of the material. The material then deformed and precisely filled the cavity of the die due to high pressure and heat caused by the friction stirring. The authors utilized the FSF approach to generate rivet like joints as followings. First, a substrate which is capable for friction stirring, i.e. an aluminum alloy plate, was put on a dissimilar material plate having holes, i.e. a steel plate. The authors call the former ‘the host member,’ the latter ‘a joined member.’ These members were put on a die having the cavity to fabricate the head of the rivet-like structure. Then FSF was conducted to form the stems and heads of the structure. Joint members are able to be stacked within the forming limit. In the study, the authors firstly conducted the proof of the concept (PoC) tests to generate rivet-like structure between steel and aluminum alloy plate and between CFRP and aluminum alloy plate, then investigated the forming conditions, i.e. tool feed rate, tool pass and the corresponding results, including the volume of the generated stem and head of the individual rivet-like structure. 3mm-thick A5083P-O aluminum alloy plates was utilized as the host member, and a 0.7mm-thick SPCE steel plate and a 0.8mm-thick CFRP plate as the joined members.

Abstract: The aim of this work is to use x-ray diffraction (XRD) technique to analyze ZnO particles prepared by the reaction between the zinc vapor and oxygen within microwave plasma. The microwave plasma was created by the interaction between the 1200-W 2.45-GHz microwave, the conductive material, and the argon-oxygen gas mixture. Due to the high effective temperature of the plasma, it was thermodynamically and kinetically possible to generate zinc vapor from the solid zinc and then reacted with the oxygen in the gas mixture to form ZnO particles. The synthesis of ZnO in the microwave plasma has been done for 10 to 15 minutes. The XRD results show that the synthesized ZnO samples have wurtzite structure. Moreover, the increasing of synthesis time from 10 to 15 minutes affects the lattice constants, the crystallite size, and the magnitude of strain in ZnO crystals.

Abstract: The aim of this work is to study the influence of x-ray diffractometer scanning parameters on the integrated intensity and full-width at half maximum (FWHM) of copper powder x-ray diffraction peaks by using statistical analysis methods. X-ray diffraction (XRD) analysis of the copper powder was accomplished using step scan mode with step sizes of 0.03^o and 0.05^o 2q, and preset time changes from 0.1-3.5 s. Integrated intensity of an x-ray peak was calculated by the numerical method. FWHM was measured as the width of Pearson VII model of the x-ray peak at the half-maximum intensity. The statistical analysis methods including linear regression and statistical hypothesis test were used to analyze the correlation between the preset time and the error on integrated intensity calculation, and the FWHM of a peak on the XRD pattern. The results from statistical analysis show that increasing the preset time from 0.1 s to 3.5 s does not affect the FWHM of an x-ray peak, but it reduces the relative error in integrated intensity calculation. Moreover, using the preset time greater than 1 s will minimize the relative error in integrated intensity calculation of an x-ray peak. While step size did not affect both the relative error in integrated intensity calculation or FWHM, the smaller step size would provide more data points for better accurate model of an x-ray peak.

Abstract: This research aims to study and describe the effect of microstructure on shape of distance amplitude correction (DAC) curve and ultrasonic inspectability of stainless steel weld joint. Two calibration blocks (side drilled hole block) were prepared from AISI 316 stainless steel plate according with ASME section V version 2013. One calibration block was varied the grain size by annealing process. The annealing temperature and holding time were 1,200 °C and 4 hours, respectively and then cooled down in furnace. AISI 316 Butt joint welding specimens were prepared to establish the artificial discontinuities. Lack of fusion and drill hole, diameter 1 and 2.5 mm, were selected to establish as discontinuities. Specimens were welded by gas tungsten arc welding and shielded metal arc welding process. Then, the gain size and microstructure of two calibration blocks were analyzed by microscope. The macrostructure, gain size and microstructure of weld joint were determined by microscope. Longitudinal and transverse wave with probe frequency 2.25 and 4 MHz and angle probe 45, 60 and 70 degrees were used to describe the effect of microstructure on shape of DAC curve and investigate the ultrasonic inspectability in stainless steel weld. The experiment results found that the ultrasonic energy of longitudinal and transverse wave in calibration blocks decreased as the gain size increased. The attenuation due to gain size affected to the shape of DAC curve. The grain size in heat effected zone (HAZ) of weld specimen is larger than base material and the ultrasonic transverse wave can detect lack of fusion and drill hole diameter 2.5 mm but cannot detect drill hole diameter 1 mm. The usefulness of this research is utilizable for searching the discontinuities in the weld zone of stainless steel by ultrasonic. The attenuation of ultrasonic energy in the weld zone of AISI 316 is usually high and the amplitude displayed at the screen is very low. This reason can be made the operator wrong result interpretation, if they did not consider about the attenuation from microstructure.

Abstract: The Magnetic Barkhausen Noise (MBN) technique can evaluate the residual stresses in carbon steel and provide information about the relationship between residual stress level and MBN signal. This research work is based on the analysis of MBN signals obtained from carbon steel samples. ASTM A36 and A516 carbon steel were used to vary the residual stress by heat treatment process with 5 conditions: annealing, normalizing, quenching in oil, quenching in water and quenching in salt water. The microstructure and hardness of samples also were varied by these heat treatment processes. Twelve samples (including base materials) were cut to analyze the microstructure and hardness by the microscope and hardness testing machine. Reference materials from each condition were established to represent the MBN signals. The MBN technique was used to evaluate the residual stresses from heat treatment process on each reference material. Then each sample was prepared to tensile specimen. All specimens were applied static tension load below yield point. The load was increased at 25 N/mm² (MPa) in increment. Each tensile stress level was measurement by MBN technique at 0 and 90 degree of direction of tension axis. The experimental results found that the MBN signal amplitude changed as the condition of heat treatment changed and the relationship between tensile stress and MBN signal showed linear correlation. This research is useful to understand and guide for establishing the reference materials for residual stress measurement by MBN technique.

Abstract: The influence of molecular weight of poly (D-lactide) (PDL) on the melt crystallization was successfully investigated by non-isothermal differential scanning calorimetry (DSC) technique. The synthesized PDLs with three different number average molecular weights (Mn) of 2.39×10⁵ (PDL1), 1.09×10⁵ (PDL2) and 0.61×10⁵ (PDL3) were utilized in this study. From DSC kinetics analysis, it was found that the rate of PDLs crystallization increased with increasing cooling rate. Furthermore, the crystallization rate of PDLs was dependent on molecular weight and determined to be in the following order: PDL3 > PDL2 > PDL1. The crystallization mechanism was analyzed by the Avrami, Ozawa and Liu models. The mechanism of all PDLs crystallization was nucleation with three dimensional growths. Furthermore, the molecular weight of PDLs affected not only the crystallization rate but also the thermal property. As the molecular weight of PDLs increased, the melting temperature (T_m) increased but the heat of melting (∆H_m) decreased.

Abstract: This study aimed to develop gelatin (GEL) and gelatin/Alpha starch (GEL/αSt) dissolving films as drug delivery by casting method. Because these films were brittle and lack of elasticity, therefore, glycerin (GLY), propylene glycol (PG) or polyethylene glycol 400 (PEG) in various amounts (5-30 part per hundred of gelatin; phg) was used as plasticizer. It was found that all types and amounts of plasticizer could be blended into gelatin solution and the transparent GEL films were formed, except the GEL/PEG films presented in opaque characteristics. However, 30 phg GLY blended film was too softy. Increasing amount of plasticizer caused a decrease in tensile strength and increase in elongation at break (EAB) of films. These GEL films swelled, dissolved and eroded in 2 hours. The αSt was also blended, and the effects of αSt amounts (5-30 phg) and plasticizer types (at 25 phg) on GEL film properties were studied. The αSt dispersions mixed well in gelatin solution and gave homogenous films. The swelling and erosion of GEL/αSt films in water were faster than those of GEL films. Increasing αSt amount prolonged the swelling time and decreased the degradation rate of GEL/αSt films. The tensile strength of GEL/αSt/GLY films slightly increased when the αSt amount increased but those of PEG and PG blended films were not different. The EAB of all plasticizer blended films decreased when the amount of αSt increased. Either lidociane or lidociane hydrochloride was mixed in GEL/αSt/GLY dissolving films to use as local anesthetic. The morphology, Fourier Transform Infrared Spectroscopy confirmed their compatibilities in these films, but Differential Scanning Calorimeter showed some changes that should be further evaluated.

Abstract: STR-5L is a high quality block rubber in Thailand that is interesting to apply in medical and pharmaceutical products because it has very low impurity but high uniformity. In this study, medicated pressure sensitive adhesive (PSA) patches were developed by melt blending technique using hydroxyethyl cellulose (HEC) as tackifier and paraffinic oil as softener. Two rolls mill was used to blend all ingredients and the thin PSA patches were rolled out. Various preparation parameters were studied such as initial viscosity of rubber (60 or 80 Mooney viscosity; MV), mastication time (5-20 minutes), step of mixing, mixing time (35-80 minutes) and gap between rollers (0.1-0.4 mm). The suitable processing conditions were optimized. It was found that the rubber having initial viscosity of 80 MV provided better physical properties, for example, higher force T-peel, lap shear strength and shear holding time. Longer mastication time increased the shear holding time of patches. At 70 minutes of mixing time, the patches showed the highest shear holding time and did not leave any residue on the testing equipment surface. Moreover, the shear holding time decreased when the gap between rollers was expanded. Mixing method with the sequential addition of STR-5L, HEC and then paraffinic oil, provided good PSA patches. However, preparation process did not affect the plasticity retention index of PSA patches due to there were not significant change of values when those all parameters were varied. Next, lidocaine or its hydrochloride salt in powder form could be blended into this PSA to be the homogeneous patches. This lidocaine PSA patches for local anesthetics application on the skin would be evaluated in further study.

Abstract: The effects of calcium carbonate (CaCO₃) concentration on crystallization behaviors and morphology of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) were investigated. Composites of PHBV with CaCO₃ were prepared with filler loadings of low (5%wt) and high concentration (20%wt) and these were subsequently compared to unloaded PHBV. The morphologies of PHBV composites on the freeze-fractured specimens were examined using scanning electron microscopy (SEM). The SEM images revealed that increasing concentration of CaCO₃ resulted in agglomeration. This agglomeration might affect crystal growth rate and mechanism. The crystal growth behavior of melt-crystallized PHBV with different amounts of CaCO₃ was studied by polarized optical microscopy (POM), while the crystal structure was examined by X-ray diffraction (XRD). The rate of crystal growth determined from POM at selected crystallization temperatures revealed that the addition of a small amount of CaCO₃ accelerated crystal growth rate, whereas excess amount of CaCO₃ had the opposite effect. The POM images were also used to illustrate the change of crystal growth process presence of CaCO₃. The unloaded PHBV clearly showed nucleation and growth mechanism, while PHBV composites displayed nucleation and then combination of crystals during the growth process. However, CaCO₃ did not affect the crystal structure of any PHBV composite as observed by XRD. Molecular weight determination via gel permeation chromatography (GPC) indicated that there was no significant difference among PHBV composites.

Abstract: Natural rubber is an important export product of Thailand, which presently contributes about 40% of global production and export. In order to make the natural rubber latex to be durable material, the proper vulcanization process is needed. In typical vulcanization process, chemical substances are added to improve the rubber properties. This may cause some problems e.g. toxicity, blooming effects and unpresented smell due to the additive substances. Vulcanization using an accelerated electron beam does not need to add possibly toxic chemical compounds, especially sulfur. Thus, it was proved to be an alternative method for high quality natural rubber vulcanization. This paper presents about simulation of electron beam irradiation for natural rubber vulcanization with variable electron beam energy and current of 0.5-4 MeV and 10-100 mA, respectively. These ranges of the electron beam energy and current will give adjustable absorb dose, which is the most important parameter for electron beam processing. The absorb energy and its distribution in the natural rubber latex are simulated by using a Monte Carlo method program, GEometry ANd Tracking 4 (GEANT4), with the aim to find the optimal conditions of electron beam properties for sufficient natural rubber vulcanization. Study results of the energy distribution for electron beam penetration in the natural rubber latex are presented and discussed in this paper.