LAB 4: Modulus of elasticity

Transcription

1 LAB 4: Modulus of elastcty 1. Preparaton: modulus of elastcty (chapter15, p.79) Hook s law graphcal determnaton of modulus of elastcty (p.8) determnaton of modulus of elastcty n tenson and flexural stress mechancal stran gauges, electrcal resstant gauges basc stran at basc loadng ( (chapter , p.84) 2. Procedure The students wll be dvded nto 3 groups, each wll measure the modulus of elastcty n the flexural stress of the dfferent materals The stran wll be measured by the electrcal resstance gauge wth the help of apparatus TSA. The prncpal of the measurng s descrbed n the chapter Scheme of measurng: F measurng gauge R 1 compensatng gauge R 2 R 3 R 4.57 varable resstance for balancng of the brdge Measurng: Materal wll be loaded gradually and after each loadng step the load goes back to the basc load F. Scheme of the loadng wll be gven at the lesson. 1. Swtch on the apparatus 2. Zero the apparatus by the button 3. Apply load F 1 on the materal. 1

2 4. After the stablzaton read the value of deformaton n promles from the dsplay and wrte t nto the table as a 1 st set of readng at the load F 1 [ ]. 5. Unload to the load F and wrte the value on the dsplay as a 1 st set at the load F [ ]. 6. Repeat the procedure from ponts 3 to 5 for the loadng F 2 and F After each loadng to F there s necessary to unload to F and wrte down the value of the deformaton 8. Durng the one loadng set the materal shouldn t be fully unloaded. 9. After one complete loadng set swtch off the apparatus. 1. Measure the cross-sectonal dmensons b, h at the place of measurng (be careful not to touch glued gauge!), each dmenson mnmally twce. 11. Measure the dstance between supports l 12. Repeat the measurng accordng ponts 1 to 9 and the results wrte down as a 2 nd set of readng 3. Protocol Modulus of elastcty n flexural stress (form LAB 4:a) Modulus of elastcty n flexural stress) determne relatve elastc deformatons (elastc stran) ε [ ] as a dfferences between readngs at loadng stages F and subsequent readng at basc load F for both sets and count ther mean value ε [ ] count the basc stran ε [ ] between zero and basc loadng F from smlarty of trangles (Fg. 44 p.84) and count the total stran (ε + ε ) [ ] for each loadng step count the stranσ [MPa] flexural stress, tenson) at each loadng step accordng the type of loadng count the modulus of elastcty E [MPa] from Hook s law count mean value of the modulus of elastcty E [MPa] from all loadng stages Modulus of elastcty n tenson (form LAB 4:a) Modulus of elastcty n flexural stress) the data, measured on the steel, wll be gven the mechancal gauges (Fg. 4 p. 81) were used for measurng determne the real deformaton l as a dfferences between readngs at loadng stages F and at basc load F count the relatve strans (relatve deformatons) ε [ ] from the real deformatons and the orgnal gauge length (l 1, l 2 ) the rest of the determnaton s the same as a determnaton of modulus of elastcty n flexural stress For protocol you can use the form attached. If you use the hand made form, t has to be smlar to ths form. 2

3 LAB 4: Modulus of elastcty Name: Sgnature: Study group: PIN: Date: Number of annexes : (all calculatons, gven data) Results: Tested materal : Modulus of elastcty n flexural stress MPa Steel Modulus of elastcty n tenson GPa 3

4 LAB 4: a) MODULUS OF ELASTICITY IN FLEXURAL STRESS Materal : Cross sectonal sze: Loadng scheme : Source of loadng : Secton modulus : [mm 3 ] Measurng apparatus : Basc stran (between and F ): F ε ε1. F1 F l M F l 4 Loadng F 1 F F 2 F F 3 F F Readng of apparatus Relatve stran durng unloadng from F to F 1 st set 2 nd set Mean.ε 4 Total stran (ε + ε ) Bendng moment M Stress M σ W Modulus of elastcty σ E ε / + ε ( ) 1 3 [N] [ ] [ ] [ ] [N. mm] [MPa] [MPa] Mean value of the modulus of elastcty:

5 LAB 4: b) MODULUS OF ELASTICITY IN TENSION Materal : STEEL Source of loadng: Press FP 1 Dameter: d1 d2 mean d Cross sectonal area: [mm 2 ] A Loadng scheme : orgnal gauge lengths:: l 1 Measurng apparatus: 2 mechancal stran gauges Basc stran (between and F t ): Ft ε ε1. F F t1 t l 2 Loadng F t F t1 F t F t2 F t F t3 F t Stran durng unloadng from F t to F t Readng of the gauges l real l relatve ε l 1 st gauge 2 nd gauge mean ε 5 Total stran (ε + ε ) Stress F t σ A Modulus of elastcty σ E ( ε / + ε ) [N] [-] [-] [MPa] [MPa] Mean value of the modulus of elastcty of steel: