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Requirements
Requirements
1. Client
The frame must withstand the loads and moment applied to it throughout the testing process.
2. User
The frame must be stable and able to hold the screw, motor, and grippers.
3. Safety
The frame’s capacity must meet or exceed the maximum capacity of the tensile testing machine’s maximum force.
4. Standard
The frame must meet or exceed the testing parameters outlined in ASTM D638.
5. Law
The frame’s design and manufacture shall not infringe upon any existing intellectual property.
6. Environment / Sustainability
All manufacturing processes in the production of the device shall conform to all applicable standards.
7. Cost Efficiency
It must be cost effective, while still meeting all requirements and standards.
8. Weight
The weight of the frame is not a critical requirement.
Specifications
Specifications
Force Capacity
0.5 [kN]
Vertical Test Space
726 [mm]
Testing Speed Range min/max (Return)
0.05-2500 [mm/min]
(1875)
Frame Axial Stiffness
8.5 [kN/mm]
Maximum Force at Full Speed
0.5 [kN]
Maximum Speed at Full Force
2500 [mm/min]
Height
104 [cm]
Width
46 [cm]
Depth
61 [cm]
Maximum Power Requirement
250 [VA]
Material and Process Selection
Material and Process Selection
The priority of the frame is to hold the motor, screw, and grippers securely and to avoid buckling and deflection. The frame must be stiff and strong. The ultimate strength is not to be consider as the frame will be designed to withstand such a load with a safety factor. Weight is not a factor but it is important to for the rails of the frame to be long enough to perform tensile tests. We also want to have the frame as short as possible in order to minimize the bending moment that will be placed on the frame while being able to perform a tensile test. It is important to consider cost and to keep it as low as possible while maintaining functionality. We want to maximize the bending stiffness of the frame.
Our prototype will be made of a homogeneous material so that calculations and design factors are all uniform and simple. Most likely, the frame will be made of some metal, but the exact process will depend on the exact one that we choose. We will be using a subtractive manufacturing process with the most likely candidate being milling or CNC milling.
Important Properties:
- Young's Modulus
- Density
Scaling
Scaling
Static Analysis
Static Analysis
Material Selection
Material Selection
In order to select a material, the main property to be considered is the modulus. We want our frame to be as stiff as possible and avoid deflection. In order to avoid buckling of the frame, we must choose a modulus of elasticity so that the frame can withstand the critical load of the motor. Which in our case is 500N.
Another factor to be considered is the bending moment the grippers will place on the frame. In order to prevent deflection, we want to choose a material that is stiff enough to withstand this.
Our frame is to have a high bending stiffness and taking a look at the Ashby chart on the left, materials with a Young's modulus in our target range contain metals, ceramics, and composites.
In order to minimize costs while maintaining a high Young's modulus, we will follow the index of E/C. Taking a look at the Ashby chart, we can imply that the materials best suited for the frame include technical ceramics, composites, metals, some nontechnical ceramics, polymers, and natural materials. By maximizing modulus, we are looking at cast irons, aluminum alloys, carbon steels, zinc alloys and silicon carbide as potential materials.
Similar considerations apply to a scaled down prototype version of its industrial equivalent.
To maximize the bending stiffness of the frame we will follow the index of E^1/2/ rho. Following this index and maximizing Young's modulus, elastomers, foams, and most polymers and natural materials are eliminated due to their lower modulus. We are left with most metals, some technical ceramics, and composites. Out of all these options, the materials with maximized modulus include, silicon carbides, boron carbides, steels, and nickel alloys.
Similar considerations apply to a scaled down prototype version of its industrial equivalent.
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