mechanics of solid lab

Lab 3: Hooke’s Law and Elastic Properties

In this lab you will design 4 experiments to explore Hooke’s Law and tensile properties. Type your responses to the questions given below and attach all plots, data, & sample calculations.

Equipment:

·

· Mass and Hanger Set

· Mass scale

· Free Springs (1 wide, 1 narrow)

· Ruler

· Caliper and/or micrometer

· Lever-and-Fulcrum Apparatus

· Rubber Bands (~9 skinny, 1 wide)

· 2 Binder clips, 3 s-hooks

Questions:

· 1) Determine the spring constant or stiffness k of two springs: a narrow one (k1) and a wide one (k2). Next, place the springs in series and experimentally determine the total elongation (delta) as a function of load F. Plot F vs. delta for the 3 data sets and determine k1 and k2 (units of N/mm). Come up with a formula to describe the elongation of springs in series as a function of F and k1 and k2 and check whether this matches your experimental results.

· 2) Generate a stress-strain curve for 1 LONG(L) rubber band and 1 SHORT(½ L) rubber band (*load only for the elastic regime not to point of failure*). Are the curves the same? Why/why not? Units of stress are MPa.

· 3) Generate a stress-strain curve for 1 narrow rubber band, 2 narrow rubber bands, and several narrow rubber bands braided together (*load only for the elastic regime not to point of failure*). Are the curves the same? Why/why not? Compare the elastic modulus E of the single, double, and braid. Discuss the cable effect!

· 4) Determine Poisson’s ratio for a wide elastic band. You will want to do more than one data point!

***Compare rubber E and v to literature values for extra credit!!!

Tips to consider:

· LEVEL the apparatus

· Record all original data, do conversion after

· Repeated measurements yield more consistent results; you should have at least 4-5 good data points for a trend or average (determine if there are true outliers)

· Is the lever-and-fulcrum apparatus may provide a mechanical advantage?

· The springs and rubber bands must not exceed their elastic limits!

· Check for slipping and always mark and measure your starting length

· Be consistent with units (report results in standard metric units)

· Record the uncertainty of EVERY measurement! And your overall uncertainty in the result.

· Everyone does their own analysis and report; however note your data collection partner(s) on your assignment.