Design and Development of a Tensile Testing System for Additive Manufactured Parts - Group 3

Project Motivation and Problem Statement Additive manufacturing has become essential for rapid prototyping and custom part production in aerospace, automotive, and medical device applications. However, the mechanical properties of 3D-printed parts depend heavily on printing parameters like layer orientation, infill density, and material choice. To validate these properties, engineers typically need access to universal testing machines that cost $30,000 or more, far beyond the budget of most university labs and small companies. Our project tackles this accessibility problem by developing a tensile testing system that costs under $500 while maintaining the accuracy needed for meaningful materials characterization of additively manufactured specimens. Engineering Approach and Methods We designed our system around three core subsystems: mechanical actuation, force measurement, and data acquisition. For the actuation mechanism, we selected a stepper motor driven linear actuator with dual rail guidance to maintain proper specimen alignment and prevent unwanted bending during tests. Force measurement uses a DYMH-103 200 kg load cell connected to an HX711 amplifier, giving us resolution down to a fraction of a Newton, precise enough for testing plastic and thin metal samples. An Arduino Nano handles motor control and samples the load cell at 10 Hz, sending data in real-time over a serial connection. We performed finite element analysis on our frame design to confirm it stays rigid under maximum load, with deflection kept under 0.1 mm throughout the entire test range. Design Implementation The physical system consists of an aluminum extrusion frame with adjustable grip spacing that accepts specimens from 50 mm to 200 mm long. Rather than buying expensive commercial grips, we designed custom wedge-style clamps that we 3D-printed ourselves. They prevent specimen slippage without creating stress concentrations that would invalidate our results. All electronics live in a single ventilated enclosure with proper terminal blocks for clean wire management. We calibrated the system using precision weights and a digital caliper, achieving load measurement accuracy within ±0.5% and displacement resolution of 0.01 mm through the stepper motor's encoder feedback. The control software lets users select different test modes, constant displacement rate or load controlled, and automatically logs all data to CSV files for analysis in MATLAB or Excel. Results and Performance Evaluation We've tested the system using PLA dog-bone specimens printed at different infill densities (50%, 75%, and 100%). The resulting stress-strain curves match what we see in published literature, which validates our measurement approach. The system handles tensile loads up to 1.2 kN with ±5 N accuracy, confirmed against calibrated reference weights. We can maintain constant crosshead speeds anywhere from 0.5 mm/min to 50 mm/min with less than 2% variation. When we calculated Young's modulus for our 100% infill PLA samples, we got 2.8 ± 0.2 GPa, within 10% of the manufacturer's reported values. The total cost for components and fabrication came to roughly $600, which represents a 99% savings compared to buying a commercial machine. Impact and Applications This project makes materials testing accessible to groups that couldn't afford it before. In educational settings, undergraduates can now get real lab experience with standardized testing procedures instead of just reading about them. For researchers and small manufacturers working with 3D printing, the system enables quick iteration on print settings to maximize part strength and implement basic quality control. We're planning future improvements like adding an extensometer for more precise strain measurement, integrating computer vision for automatic specimen detection, and expanding to cyclic fatigue and creep testing. By documenting our design as open-source, we hope others will build their own systems and contribute to a shared database of material properties for different 3D printing materials and processes.