AbstrakSinyal atau gelombang merupakan salah satu phenomena fisik yang telah banyak diaplikasi dibidang sains dan teknologi untuk mengkarakterisasi suatu bahan, seperti retakan dan kandungan dari material, dan nada. Sifat fisik yang digunakan untuk mengkarakterisasi bahan adalah frekuensi. Frekuensi yang dihasilkan oleh manusia berberda-berbeda dikarenakan tekanan, pita suara juga berbeda-beda. Penekanan suara dapat dikarakterisasi dalam domain waktu, sedangkan frekuensinya dapat dikarakterisasi dalam domain frekuensi. Untuk mengkaraterisasi, nada tersebut direkam dengan menggunakan microphone. Hasil rekaman tersebut akan tersimpan di dalam soundcard yang terintegrasi dengan personal computer (PC), kemudian dianalisis dengan menggunakan algoritma yang diimplementasi kedalam matlab. Algortima tersebut adalah algoritma recording dan discrete Fourier transform (DFT). Windows leakage dapat diminimalisasi menggunakan algoritma Blackmann dan Barthannwin modified. Frekuensi ,dan amplitudo yang dihasilkan oleh nada darihuruf vokala dalahnada I adalah 190 Hz dengan amplitudo 0,14 dB, nada o adalah 580 Hz dengan amplitudo 0,1 dB, nada u adalah 210 Hz dengan amplitudo 0,15 dB, nada e adalah 200 Hz dengan amplitudo 0,13 dB, dan nada aadalah 310 Hz dengan 0,1 dB.Noise yang dihasilkan oleh nada o pada saat pengambilan data disebabkan oleh perangkat personal computer (PC). Kata kunci: Discrete Fourier transform, algoritma Blackmann dan Barthannwin modified
Leaf spring is one of a component of the vehicle which is used to vibration damping caused by the force. Some of case that occur in the vehicle namely overload where this case can affect to fatigue life of steel leaf spring. One of method that is use to fatigue life prediction is the high fatigue cycle, and this method can be simulated by a finite element method. The numbers of both elements and nodes that have been used in this research are 6961 elements and 14726 nodes, respectively. The magnitude of the force that is applied to prediction fatigue life of leaf spring are 80 KN, 100 KN, and 200 KN. Based of the finite element analysis, fatigue life of the force 80 KN longer than force 200 KN and 200 KN was obtained which is a desired 10 6 cycle. Also, the critical value of the fatigue life 80 KN is smaller than 100 KN, and 200 KN. As such, the force 80 KN is a recommended as an allowed force which use to vehicle. This value is validated by safety factor analysis where the force allowed as 80 KN with safety factor equal to 2.56.
Leaf spring is one of component that use to vibration damping on vehicle, where one of material that use to fabrication this component is 55Si7 steel. Currently, sustainable product is main focus in industry, so that composite is a potential alternative to replace steel as leaf spring. Materials that use to composite fabrication are sisal as fiber, epoxy as matrix, and honeycomb and alumunium alloy as core, where fabrication both 55Si7 steel and composite specimen are based on ASTM D638 standard. Fabrication of composite specimen conducted by hand lay-up technique, and mechanical properties analysis of thus specimen are conducted by finite element method. Tensile test is tested on 55Si7 steel and composite specimen using finite element method. According tensile test, steel of 55Si7 type have 2.92 mm of total deformation average, and 12583 MPa of strain, composite natural fiber with honeycomb core have 62.75 mm of total deformasi average, and 18590 MPa of stress, and composite natural fiber with aluminium alloy core have 15.47 mm of total deformasi average, and 12813 MPa of stress. According that results, composite with aluminium alloy core have the mechanical properties close to 55Si7 steel than composite honeycomb core.
The mechanical properties of natural fibers are continuous development as the alternatively synthetic fibers because of the natural fibers are non-corrosive, lightweight, and environmental advantages. However, these fibers have poor interfacial adhesion properties as the fibers if used as bio-composite material. This problem can be solved by the surface modification method by the sodium hydroxide treatment used to improve the mechanical properties. A sodium hydroxide concentration which it used at 0 wt%, 5 wt%, 10 wt%, and 15 wt% and the sisal fibers were soaked in that a concentration for 2 hours. Furthermore, the bio-composite fabrication is conducted by hand lay-up technique which is using both sisals as the fibers and epoxy resin as the matrix. The tensile test RTG-1250 results show that the maximum mechanical properties, such as strains, Young's modulus, and elongation, was obtained at sodium hydroxide 5 wt% than others where the values of these mechanical properties were 25.334 MPa, 16.111 GPa, and 1.572%, respectively. The morphological evaluation carried out using a scanning electron microscope showed that the alkali sodium hydroxide treatment was improved interfacial adhesion between fiber and matrix. Finally, sodium hydroxide alkali treatment of more than 5% can be able to sisal fiber cracks so that the mechanical properties of bio-composite can decrease continuously.
Single leaf spring is one of the suspension systems on vehicles that function as vibration dampers which usually use steel. One type of steel that is often used in making single leaf springs is 55Si7 steel. However, at this time composite materials began to be used as an alternative material to replace steel. One of the composite materials used as a substitute for steel is E-glass epoxy. This study aims to determine differences in the characteristics of steel leaf springs and e-glass epoxy composites. In addition, the effect of orientation of the fiber direction to deformation, stress, and safety factors on leaf springs was also carried out in this study. The analytical method used is finite element. The results showed that the composite leaf springs had lower stress than steel leaf springs. E-glass epoxy composite leaf springs variation D (fiber orientation 45º / -45º) showed the lowest stress and highest safety factor with values of 596 MPa and 1.4 respectively.
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