String Tension Tester

Introduction

In many engineering projects, it is critically important to know the strength of a material in a design. A material’s strength is a measure of its ability to withstand an applied tension, compression, or shear force. Tension or tensile forces pull on a material. Compression or compressive forces push on a material. Shear forces are two pushing forces that are offset from one another (like the forces used by a pair of scissors to cut paper). The ultimate strength of the material is the point at which it fails under one of these conditions. Tension, compression, and shear strengths can be quite different depending upon the material; for example, most metals are much stronger in tension than they are in shear. Concrete is stronger in compression than it is in tension.

In this project, your challenge is to build a robotic device to test the tension strength of string, fishing line, and/or sewing thread. Many of these come rated by tensile strength, which is the weight (tensile force) they can support before breaking.

Objectives

In this project, you will design and build a robotic device for testing the strength of a piece of string. Sewing thread, light fishing line and yarn are good choices for string to test. One end of the string should be tied to the hook of the Vernier Dual-Range Force Sensor with the other end pulled by the robotic device. The device should be able to pull the string at a slow and steady rate until the string breaks. Simultaneously, your program should either graph the data in real time or store it in a text file for future graphing so that the maximum tensile strength can be determined using the NXT Data Logging analysis tools. The string samples should be easy to load and unload.