This paper reports the fatigue analysis for a failure of a shaft in a wind turbine in which reinforced-welding elbow to support the shaft load. The shaft was broken near the reinforcing elbow. When designing mechanical and structural components, the diameter and the characteristics of materials have been considered not to exceed the permissible limit. However, after 40 days of the cycle operation, the shaft was broken at the accepted loading conditions within reasonable limits at a wind speed of 6-10 m/s. The crack initiate fatigue in the shaft is influenced by many variables that may due to uniaxial, bending, torsion, the shape of loading curve, part size, part finish, operating temperature, and atmosphere. For these reasons, it is important to investigate the fatigue behavior on the failure of the shaft. The main goal is to investigate and analyze the fatigue behavior on a broken shaft of the wind turbine gearbox to determine the features that cause the failure. A microscopic investigation of the fatigue-fracture surface was done. The microscopic analysis was carried out in terms of the chemical composition using ARL Spark Spectrometer, energy dispersive spectroscopy (EDS), the morphology of the fatigue by using scanning electron microscopy (SEM) and hardness test. Moreover, a theoretical analysis was made to illustrate the results and comparison between these results and the corresponding stress distribution data from a finite element method (FEM) simulation to know how the fatigue fracture began and propagated along the shaft. The result of the analysis shows that the fatigue occurred due to the unbalanced of the bending and torsion stress in the junction of the reinforced-welding elbow with hardness testing at the extreme cracking area is 435 HV. It is emphasized that the microstructure of fatigue surface structure shows sensitization to facilitate intergranular cracking and fatigue corrosion.

Pelumas merupakan salah satu bahan yang penting dalam pengoperasian mesin kapal agar bekerja secara optimal, dan memberikan pelumas yang salah dapat mengakibatkan mesin mengalami kerusakan. Sedangkan Viskositas (Viscosity), adalah suatu angka yang menyatakan besarnya perlawanan/hambatan dari suatu bahan cair untuk mengalir atau ukuran besarnya tahanan geser dari bahan cair. Tujuan dari analisis sampel pelumas (Shell Rimula R4X 15W 40) di laboratorium ini adalah untuk mengetahui kondisi pelumas dan penyebab viskositas pelumas turun dari dua sampel pelumas (oli baru dan oli setelah tergunakan dengan jam kerja pelumas 312 jam).Hasil dari analisa sampel pelumas di laboratorium ini menunjukan bahwa kondisi dari dua sampel pelumas tidak normal. Dilihat dari uji fisik viskositas uji nilai di oli baru 11.33 seharusnya pada oli normal uji fisik Viskositas 100ºC uji nilai 14.7. Uji nilai TBN 17.1. Uji nilai Oksidasi 0.56 apabila oli baru seharusnya nilai Oksidasi 0 karena belum mengalami proses operasi mesin, indikasi oli baru itu adalah oli bekas, atau indikasi oli palsu. Dilihat dari uji fisik Viskositas uji nilai di oli setelah tergunakan 11.00, terindikasi mesin yang Overheat, karena tercampurnya bahan bakar, dilihat bahan bakar dengan Destilasi uji nilai 0.5 adanya kebocoran bahan bakar. Uji nilai TBN 15.03, normal karena TBN menetralisir asam sulfur di bahan bakar. Jadi hasil pengujian sampel pelumas merk Shell Rimula R4X 15W 40 olibaru dan oli setelah digunakan mengalami penurunan nilai viskositas.