Electronic Theses and Dissertation

Exhaust valve merupakan komponen penting pada mesin diesel yang bekerja pada kondisi temperatur dan tekanan tinggi serta mengalami pembebanan siklik selama operasi. kegagalan pada komponen ini dapat menyebabkan penurunan performa mesin dan meningkatkan risiko kerusakan lanjutan. penelitian ini bertujuan untuk menganalisis mekanisme kegagalan exhaust valve mesin diesel menggunakan metode eksperimental. tahapan penelitian meliputi pengamatan visual, pengujian kekerasan, analisis komposisi kimia, pengamatan struktur mikro, serta analisis permukaan patahan menggunakan scanning electron microscope (sem). selain itu, dilakukan analisis tegangan dan evaluasi potensi buckling pada batang exhaust valve. hasil penelitian menunjukkan bahwa material exhaust valve tergolong baja tahan panas austenitik 21-4n, namun kandungan kromium dan nikel yang relatif lebih rendah dari standar menurunkan ketahanan oksidasi dan stabilitas, mikrostruktur nya terdiri dari pearlite dan ferrite.. nilai kekerasan rata-rata sebesar 341,7 vhn dengan variasi antar titik pengujian menunjukkan pengaruh siklus termal selama pengoperasian. berdasarkan analisis euler, beban kritis buckling batang exhaust valve diperoleh sebesar ±49 kn. tegangan kerja sebesar 31,9 mpa masih berada di bawah tegangan luluh material 21-4n (154 mpa), yang mengindikasikan bahwa kegagalan terjadi akibat ketidakstabilan struktural (buckling), bukan karena luluh material.hasil pengamatan sem menunjukkan mekanisme kegagalan berupa kelelahan termo-mekanik yang diawali inisiasi retak, diikuti perambatan retak, dan diakhiri patahan ulet. penelitian ini diharapkan dapat menjadi referensi dalam upaya pencegahan kegagalan exhaust valve pada mesin diesel.

The exhaust valve is a critical component in diesel engines that operates under high temperature and pressure conditions and is subjected to cyclic loading during service. Failure of this component can lead to reduced engine performance and an increased risk of secondary damage. This study aims to analyze the failure mechanism of a diesel engine exhaust valve using an experimental approach. The research stages include visual inspection, hardness testing, chemical composition analysis, microstructural observation, and fracture surface analysis using a Scanning Electron Microscope (SEM). In addition, stress analysis and evaluation of the buckling potential of the exhaust valve stem were conducted. The results indicate that the exhaust valve material is classified as austenitic heat-resistant steel 21-4N; however, the chromium and nickel contents, which are relatively lower than standard values, reduce oxidation resistance and microstructural stability. The microstructure consists of pearlite and ferrite phases. The average hardness value obtained was 341.7 VHN, with variations among test points indicating the influence of thermal cycling during operation. Based on Euler analysis, the critical buckling load of the exhaust valve stem was approximately ±49 kN. The calculated working stress of 31.9 MPa remained below the yield strength of the 21-4N material (154 MPa), indicating that the failure was primarily caused by structural instability (buckling) rather than material yielding.. SEM observations reveal that the failure mechanism is dominated by thermo-mechanical fatigue, characterized by crack initiation, crack propagation, and final ductile fracture. This study is expected to serve as a reference for preventing exhaust valve failures in diesel engines.