IMPROVEMENT ON SEVERAL PHYSICAL AND MECHANICAL PROPERTIES OF JATI UTAMA NUSANTARA WOOD BY THERMAL COMPRESSION TREATMENT

Jati Utama Nusantara (JUN) adalah salah satu tipe jati (Tectona grandis Linn. F) cepat tumbuh yang berasal dari Jati Plus Perhutani (JPP). Pohon JUN memiliki sedikit percabangan dan batang yang lebih berbentuk silinder serta menunjukkan pertumbuhan yang lebih cepat dibandingkan jati budidaya dari biji (konvensional), sehingga dapat dipanen dalam waktu singkat. Meskipun cepat tumbuh, berbagai penelitian menunjukkan kayu JUN belum memenuhi standar SNI 01-0608 sebagai bahan baku furnitur. Penelitian ini bertujuan untuk meningkatkan beberapa sifat fisis dan mekanis kayu JUN umur muda melalui perlakuan pemadatan menggunakan kempa panas. Contoh uji kayu JUN umur 5 tahun berukuran 2,5 cm (tebal/radial), 10 cm (lebar/tangensial), dan 30 cm (panjang/longitudinal) diberi tekanan sebesar 25 kg/cm2 selama 40 menit dengan 3 perlakuan suhu, yaitu 170°C, 180°C, dan 190°C. Pengujian sifat fisis dan mekanis kayu mengacu pada standar ASTM D143. Perubahan kristalinitas kayu diamati menggunakan X-ray Diffractometer (XRD), dan permukaan kayu diamati secara visual. Sebagai penunjang, pengamatan struktur sel kayu dilakukan menggunakan mikroskop stereo (Zeiss). Hasil penelitian menunjukkan bahwa contoh uji kayu JUN yang diberi perlakuan tekan-panas dapat memperbaiki sifat fisis dan mekanisnya dibandingkan contoh uji kayu JUN tanpa perlakuan (kontrol). Berdasarkan hasil simulasi data, sifat fisis dan mekanis contoh uji terbaik diperoleh pada suhu kempa sekitar 185°C.

Flow Stress Behavior and Microstructure Evolution of Austenitic Stainless Steel with Low Copper Content during Hot Compression Deformation

In order to study the microstructure evolution and flow stress behavior of as cast antibacterial austenitic stainless steel containing 1.52 wt.% copper, Gleeble 3800 was used for thermal compression simulation test. Through OM and EBSD analysis, it is found that the dynamic recrystallization mechanism of thermal deformation is mainly discontinuous dynamic recrystallization. With the increase of deformation temperature and deformation rate, the proportion of recrystallization nucleation gradually increases. The growth of twins relies on recrystallization and, at the same time, promotes dynamic recrystallization. Considering the influence of strain on flow stress, the strain compensation Arrhenius model is established according to the obtained stress-strain curve, and high accuracy is obtained. The correlation coefficient and average relative absolute error are 0.979 and 7.066% respectively. These results provide basic guidance for the technology of microstructure control and excellent mechanical properties of antibacterial stainless steel.

Manufacturing Process of Polymeric Microneedle Sensors for Mass Production

In this work, we present a fabrication process for microneedle sensors made of polylactic acid (PLA), which can be utilized for the electrochemical detection of various biomarkers in interstitial fluid. Microneedles were fabricated by the thermal compression molding of PLA into a laser machined polytetrafluoroethylene (PTFE) mold. Sensor fabrication was completed by forming working, counter, and reference electrodes on each sensor surface by Au sputtering through a stencil mask, followed by laser dicing to separate individual sensors from the substrate. The devised series of processes was designed to be suitable for mass production, where multiple microneedle sensors can be produced at once on a 4-inch wafer. The operational stability of the fabricated sensors was confirmed by linear sweep voltammetry and cyclic voltammetry at the range of working potentials of various biochemical molecules in interstitial fluid.

Low Sintering Temperature Nano-Silver Pastes with High Bonding Strength by Adding Silver 2-Ethylhexanoate

A silver precursor (silver 2-ethylhexanoate) and silver nanoparticles were synthesized and used to prepare a low sintering temperature nano-silver paste (PM03). We optimized the amount of silver 2-ethylhexanoate added and the sintering temperature to obtain the best performance of the nano-silver paste. The relationship between the microstructures and properties of the paste was studied. The addition of silver 2-ethylhexanoate resulted in less porosity, leading to lower resistivity and higher shear strength. Thermal compression of the paste PM03 at 250 °C with 10 MPa pressure for 30 min was found to be the proper condition for copper-to-copper bonding. The resistivity was (3.50 ± 0.02) × 10−7 Ω∙m, and the shear strength was 57.48 MPa.

Hot Deformation Behavior and Dynamic Recrystallization of Ultra High Strength Steel

In this paper, in order to improve the microstructure uniformity of an ultra-high strength martensitic steel with a strength greater than 2500 MPa developed by multi-directional forging in the laboratory, a single-pass hot compression experiment with the strain rate of 0.01 to 1 s−1 and a temperature of 800 to 1150 °C was conducted. Based on the experimental data, the material parameters were determined, the constitutive model considering the influence of work hardening, the recrystallization softening on the dislocation density, and the recrystallized grain size model were established. After introducing the model into the finite element software DEFORM-3D, the thermal compression experiment was simulated, and the results were consistent with the experimental results. The rule for obtaining forging stock with a uniform and refinement microstructure was acquired by comparing the simulation and the experimental results, which are helpful to formulate an appropriate forging process.

Examining Parameters of Surface Quality Performance of Paulownia Wood Materials Modified by Thermal Compression Technique

The aim of this study was to evaluate the effect of thermal compression process on some surface properties of paulownia solid wood materials. The widest surface of wood samples was mechanically compressed at high temperatures. The duration was 45 min. Four different process combinations were created, including two temperatures (150 °C and 170 °C) and two pressure levels (20 bar and 22.5 bar). The surface roughness, wettability and color properties of treated and untreated samples were compared. The roughness properties, both parallel and perpendicular to grain direction, were determined according to JIS B 0601:1994 standard. The contact angle changes of water dripped to the surface were measured according to time. For color properties, a spectrophotometer was used according to CIE L*a*b* system. The color changes were classified according to a grading method from literature. The most remarkable results on wettability were observed. The contact angle values significantly increased with this method. Although higher temperature increased the contact angle values, higher pressures did not change the values. When the surface roughness values were generally considered, this technique could decrease the values up to 40 % ratio according to the control group. Only the combination of 150 °C and 20 bar did not significantly change the values. Lastly, the results of color properties showed that all treatment parameters significantly affected total color change values of samples. Grading results were similar and the color change of modified samples graded as the lowest color difference, except with the combination of 150 °C and 20 bar. The combination of 170 °C and 22.5 bar (highest treatment conditions) significantly changed all color characteristics of samples, except b* parameter. The results of this research showed that mechanical thermal compression method could change surface properties of this fast-growing species.