Uji Lelah (Fatigue)

Summary

This video provides an in-depth demonstration of a rotary bending test (Pengujian Petik) using a specialized machine. The speaker walks through the preparation of samples, including surface sanding, and the setup of the machine. The process involves applying bending stress to test material properties, such as fracture behavior. Observations are made on past test results, showing how samples break in a brittle manner. The session concludes with a brief discussion of the significance of the test in material analysis.

Takeaways

• 😀 The script discusses the process of conducting a bending test (pengujian petik) on material samples.
• 😀 The speaker emphasizes the importance of surface preparation, requiring the samples to be sanded with a specific grit size (e.g., 400 or 800) before testing.
• 😀 The samples being tested exhibit varying thickness and some signs of corrosion due to prolonged storage.
• 😀 There are two types of samples: uniform and non-uniform in shape, providing a comparative view of material behavior.
• 😀 The testing machine used is a rotary bending machine, which rotates the sample while applying bending loads.
• 😀 The machine setup includes a motor for rotation, bearings for stability, and a load application system with adjustable parameters.
• 😀 A crucial step in the test setup involves placing the sample correctly and ensuring it is positioned in the middle of the machine's fixture.
• 😀 The bending load is applied through a lever arm, and the frequency of rotation can be adjusted using an inverter.
• 😀 Continuous monitoring of the test is essential to ensure the machine does not stop and that the load is consistently applied.
• 😀 Once the sample breaks, the fracture surface is examined to determine the nature of the material's failure (e.g., brittle or ductile).
• 😀 The test provides insights into the material's behavior under stress and its potential to withstand bending forces without failure.

Q & A

What is the main purpose of the 'petik' test demonstrated in the video?

The main purpose of the 'petik' test is to evaluate the performance of material samples under bending fatigue conditions, specifically examining how they handle repeated stress and their failure characteristics.

Why is surface roughness important in the petik test?

Surface roughness is crucial because it can significantly affect the results of the test. A rougher surface may lead to earlier material failure, so the samples need to be properly sanded before testing to ensure accurate results.

What are the differences between the two sample types shown in the video?

The two sample types differ in their section reductions. One sample has a uniform reduction, similar to a tensile test, while the other has an irregular reduction, which can influence how they respond to bending stress.

How does the rotary bending machine work?

The rotary bending machine applies stress to the samples by rotating them while they are subjected to a bending force. This is achieved by a motor that turns the sample, a flexible coupling, and bearings that stabilize the rotation. A lever arm mechanism applies the load.

What is the role of the inverter in the testing machine?

The inverter controls the frequency of the motor's rotation. This frequency corresponds to the number of rotations per second and allows the operator to adjust the testing parameters for different material stress conditions.

What is the significance of the 'reduction' section in the sample?

The 'reduction' section is the part of the sample where the cross-section has been narrowed. It is where the sample is most likely to fail under stress. This section is critical in observing how materials break under repeated load cycles.

How are the samples mounted in the rotary bending machine?

The samples are mounted in the machine by securing them in place with bearings and ensuring the reduced section is centered properly. The setup involves aligning the sample with key components like the motor and the lever arm.

What happens to the samples during the test?

During the test, the samples are rotated while being subjected to a bending force. The force is applied continuously, and the samples undergo repeated stress cycles until they fail, typically at the reduced section.

What type of fracture do the samples typically experience?

The samples typically experience brittle fractures, meaning the material breaks suddenly and without significant deformation. The fractures occur in the reduced section of the sample, as it is the weakest point.

Why is it important to maintain continuous operation of the machine during the test?

It is important to maintain continuous operation to ensure that the samples undergo the full range of stress cycles necessary for an accurate assessment of their fatigue resistance. Stopping the machine would invalidate the results.