Simple Stresses in Machine Parts

2. Simple Stresses in Machine Parts • Introduction • Load • Stress • Strain • Tensile stress & strain • Compressive stress & strain • Shear stress & strain • Young’s modulus • Shear stress or modulus of rigidity • Bearing stress

3. Introduction In engineering practice, padakomponen-komponenmesinbekerjagaya-gaya yang terdiridarisatuataulebihgaya-gayaberikutini: • Energy transmitted • Beratmesin • Frictional resistances • Inertia of reciprocating parts • Perubahantemperatur, dsb.

4. Load (beban) Definisi: sembaranggayaluar yang bekerjapadasuatukomponenmesin. Adatigajenisbeban : • Dead or steady load • Live or varying load • Suddenly applied or Shock load Suatukomponenmesinlebihmudahmenahanbebanmatidaripadabebanhidup, danlebihtahanterhadapbebanhidupdaripadabebankejut.

5. Stress (tegangan) Ketikaadasuatusistemgayaluarataubebanbekerjapadasuatubenda, makapadasetiappotonganmelintangbendatersebutakanmunculgayadalam (internal forces: besarnyasamatetapiarahnyaberlawanan) menahanbebantersebut. Gaya dalam per satuanluaspenampangmelintangbendatersebut : stress.

6. Mathematically :

7. Strain (regangan) Besarnyadeformasi per satuanpanjang : strain.

8. Tensile stress&strain x P P x P P ft ft

9. Compressive stress&strain x P P x P P ft ft

10. Shear stress&strain P P P P

11. Modulus Young Hukum Hooke bilasuatu material dibebanidalambataselastisnya, makategangan yang bekerjaakanproporsionalterhadapregangan.

12. Shear Modulus atau modulus of rigidity Experimentally: bilasuatu material dibebanidalambataselastisnya, makategangangeser yang bekerjaakanproporsionalterhadapregangangesernya.

13. Tabelharga E dan G untukbeberapa material yang seringdipakaisehari-hari

14. Bearing stress Definisi: tegangantekanlokal yang bekerjapadasuatuluasankontakantaradua members (komponen). Tergantungdaribentukpermukaankontakdan properties kedua material tegangankontakbiasanyadihitungdenganmembagibeban yang bekerjaterhadapluasankontak pin P

15. Contoh A rectangular base plate is fixed at each of its four corners by a 20 mm diameter bolt and nuts as shown in Fig. The plate rests on washer of 22 mm internal diameter and 50 mm external diameter. Copper washer which are placed between the nut and the plate are 22 mm internal diameter and 44 mm external diameter. If the base plate carries a load of 12 tonnes (including self weight, which is equally distributed on the four corners), calculate the stress on the lower washer before the nuts are tightened. What could be the stress in the upper and lower washer, when the nuts are tightened so as to produce a tension of 500 kg on each bolt ?

16. Tugas A pull of 80 kN is transmitted from a bar X to the bar Y through a pin as shown in fig. If the maximum permissible tensile stress in the bar is 100 N/mm2 and the permissible shear stress in the pin is 80 N/mm2, find the diameter of bars and of the pin. • Dikumpulhariini (senin, 08 feb 2010) nilaimaksimum 100 • Dikumpulselasanilaimaksimum 75 • Dikumpulrabunilaimaksimum 60 • Dikumpulkamisnilaimaksimum 40