Pennsy Advantages

  • High elongation, 33%
  • Less Brittle and more malleable
  • Excellent wear resistance
  • Easy and safe pop-in installation
  • Eliminates Pedestal Roof wear, drastically reducing costly repairs.
  • No pre-induced stress
Pedestal Roof Liner

Introduction

Current pedestal roof liners have a short product life.Cracked pedestal roof liners must be replaced in accordance with Rule 48 A.8 of the AAR Interchange Rules. The AAR billing for this repair is $116.47.At some locations FRA inspectors consider cracked pedestal roof liners an FRA defect!This report will summarize our FEA study and physical testing done to identify failure modes and gauge product durability.

Our investigation is ongoing.

Dyna-Clip
Dyna-Clip

Why pedestal roof liners fail

Elongation–
Current pedestal roof liners are made from a metal that has low elongation. When energy is input into a part it causes excess elongation which leads to stress cracking.

Tensile strength –
Many falsely believe that by solely addressing tensile strength cracking issues can be resolved. Tensile strength can be increased by material choice or by simply increasing the thickness of the specimen. Transdyne made their Dyna-Clip thicker with this belief. This modification will only delay failure and will actually exacerbate some modes of failure.
If the materials ultimate elongation is never exceeded, tensile strength becomes irrelevant.

Hardness –
Harder materials tend to be more brittle and have lower elongation, though harder materials tend to have better wear properties, this advantage is never realized due to premature part failure. Brittle materials also tend to fail quickly with high impacts.

Why pedestal roof liners fail

Pre-induced stress –
Materials in a state of stress will seek to release stress through elongation, cracking, and the formation of heat. The original Transdyne pedestal roof liner is applied by a clipping mechanism that flexes the part beyond its natural shape.The part seeks to return to is original shape, that of zero energy state, which the sideframe prevents. The degree in which the part is deformed beyond its “zero state” depends upon the variations found within each individual sideframe. Sideframes with larger widths pedestal roofs will stretch the part to a greater extent, thereby introducing greater stresses and facilitating quicker failures. Variations in heat treatment will also effect the stress state of the part.

Also, the current part is not flat in it original state though it must conform to a flat interface in real life applications. This too prevents the part from being a in a “zero” energy state.

Pre-induced Stress

Point loading –
The geometry of the bearing adapter creates a potential failure mode similar to that of a three point bending flexural test. Thethree point bending flexural test measures bend or fracture strength of a material. Low elongation and high hardness materials do poorly in this testing.

Also, the interface between the pedestal roof and the bearing adapter is imperfect and rough. Sharp edges or points can greatly contribute to premature failure.

Point Loading

Pedestal Roof Liner FEA Pennsy Corp vs. TransDyne

All parts are not created equal.

FEA will show that pre-induced stress contributes to a premature failure of the Transdyne parts. Pennsy parts do not have pre-induced stress as they are not made of spring steel and are not heat treated.

FEA will show that low elongation parts, regardless of tensile strength, will ultimately fail sooner than lower tensile strength material with higher elongation.

Pennsy vs TransDyne

PRL FEA Setup

Static FEA Study
Forces and Displacements

  • 50,000 lbs vert. force to top of sideframe
    • Simulation of sideframe driving down onto the PRL
  • 0.15′ horizontal displacement of each clip
  • PRL
    • Note: Displacement of tabs is negligible to stress throughout body of Pennsy PRL
Boundary Conditions

  • Fixed Adapter
    • Bottom face fixed to simulate the support of the PRL
  • No-penetration contact between all bodies
    • Condition will prevent bodies from intersection during simulation

    Boundty Conditions

Pedestal Roof Liner FEA Material Properties

Pedestal Roof Liner FEA Material Properties

FEA Results – Von Mises Stress

Yielding begins when the elastic energy of distortion reaches a critical value

Yielding begins when the elastic energy of distortion reaches a critical value

Von Mises Stress

Dyna-Clip Clip Failure

Dyna Clip Failure
The design of the Dyna-Clip’s clipping feature creates a preloaded stress within the “neck” of the part.

The FEA shows a critical amount of stress within this section when the clips are displaced 0.15″, the amount of flexure force required to attach the part.

The combination of this preloaded stress and vertical loading can result in a failed part, as seen in the picture to the left.

dyna clip failure

Dyna-Clip Clip Failure

FEA Conclusions

The Pennsy Pedestal Roof Liner shows significantly less stress than the competitive parts by means of a different clipping action.

The clip-on wear liner design shows significant stress, beyond it yield strength when flexed open to a distance needed to fit onto a sideframe. Additional stress is introduced by forcing the flattening of the bowed surface of the adapter.

The Dyna-Clip shows significant stress beyond the yield strength in the neck due to the flexing of the tabs to fit onto a sideframe.

FEA Results

FEA Results

Physical Testing

Pennsy developed a test machine and fixture to replicate the interface and interaction a PRL will be subjected to.

For testing of the PRL, the test machine will be cycling a vertical force of 20,000 lbs @ 1 hz through the side frame fixture on to a bearing adapter.

This testing proved to be slow due equipment deficiencies. The test machine was limited to 20,000 lbs vertical force.

Physical Testing

Physical Testing

Accelerated Test Modification

The architectural change to the sideframe test fixture was introduced to increase stress within the PRLs and reduce testing time.

The modification consists of a thin block, 5 inches long and 1/16” thick, welded onto the sideframe interface.

This block was positioned to correspond to the indentation on the surface of the bearing adapter. This block will increase the point loading on the PRLs thereby shortening testing time.

Accelerated Testing

Accelerated Testing

Clip-On Failure

Clip-ON Failure

Dyna-Clip Failure

Dyna Clip Failure

Pennsy Testing

Pennsy Testing

Summary

Current pedestal roof wear liners are made with a high carbon spring steel which is low in elongation, high in hardness and brittle by nature.

In addition, they are formed into their desired shape, then heat treated to make a part which material properties are primarily designed to clip to a sideframe. The attachment mechanism is flawed as it imparts stress into the part before it even sees railroad forces. Testing shows that even under low loads, 20,000lbs, these parts suffer catastrophic failures in a short period of time.

Pennsy’s pedestal roof liner will significantly outlast competitors parts for two reasons. This part was designed to clip onto a sideframe in a way that does not preload the part with stress. In addition, the material selected allows the PRL to withstand impacts and point loading without cracking.