失效及缺陷组织照片

leomet · 发表于 2015-11-13 16:52:15

本帖最后由 leomet 于 2015-12-4 20:36 编辑

Torsion bar failed at 50000 Km.

leomet · 发表于 2015-11-15 10:47:55

本帖最后由 leomet 于 2015-11-15 10:53 编辑

Subsurface crack origin at larger magnification.

leomet · 发表于 2015-11-22 08:03:01

More photos showing crack origin at different angles.

leomet · 发表于 2015-11-22 08:09:22

本帖最后由 leomet 于 2015-11-28 15:37 编辑

The dent on the torsion bar is the culprit of this fatigue fracture.

The dent was made by an accidental, careless impact after powder coating.

leomet · 发表于 2015-11-28 15:33:20

本帖最后由 leomet 于 2015-12-4 20:27 编辑

撞擊凹痕起裂點 → 發展成起裂面 1  → 發展出疲勞(緩)裂面2 → 最後: 過載(驟)裂面

                           1: (與軸線呈45°角)          2: (受帶狀組織引導轉而與軸線平行,)

leomet · 发表于 2015-12-19 18:15:19

本帖最后由 leomet 于 2015-12-20 22:56 编辑

Inter-dendritic pores in the QT 600 test bar which failed its tensile test by only 240 Mpa. Dark oxided area is micro-voids that was interconnected to the open air after freezing.

Sharp points of the shrinkage pore served as stress raisers, and thus, crack initiation sites. This is the reason why its tensile stress got so low.

leomet · 发表于 2015-12-27 23:03:26

HK焊接焊道..............

leomet · 发表于 2016-3-22 18:11:09

A fatigue crack surface. Origin found to be a corrosion pit.

What caused the corrosion reaction? Well, it's a hard nut to crack.

路冰 · 发表于 2016-5-5 15:36:00

太帮了，学到了很多知识，谢谢

猪头三 · 发表于 2016-6-8 11:30:55

很有营养！leomet 老师！请常赐教！

leomet · 发表于 2016-6-12 16:44:06

本帖最后由 leomet 于 2016-6-12 17:51 编辑

leomet 发表于 2016-3-22 18:11
A fatigue crack surface. Origin found to be a corrosion pit.

What caused the corrosion reaction? ...

This tooling is called "core rod" for making holes in PM parts.
Its material is CPM 15V. Very fine iron powders "cold welded" onto its surface during powder compacting, forming a Galvanic couple in which the CPM 15V is positive while iron powder is negative in polarity. Therefore corrosion pits created on the CPM 15V rod surface. Under tensile stress, microcrack iniitated, propagated and finally, the rod fractured.

leomet · 发表于 2016-6-12 17:21:20

本帖最后由 leomet 于 2016-6-12 17:55 编辑

Macro and SEM photos of the core rod (rough surface) and welded iron powder (smooth surface surrounded by small arrows).
細小鐵粉粘黏到心棒表面 → 產生蝕孔 → 造成疲勞破斷.

leomet · 发表于 2016-6-12 19:00:35

本帖最后由 leomet 于 2016-6-12 19:03 编辑

Fatigue failure of "hammering shafts". Life span: 1.4 and 1.9 hour during testing.

傻瓜相機+ 日光照的.

leomet · 发表于 2016-8-13 15:33:39

本帖最后由 leomet 于 2017-12-9 13:50 编辑

leomet 发表于 2015-11-9 17:06
淺蝕後又拋光, 再重蝕, 所以孿晶碳化物薄片有點碎裂.

http://www.rclbbs.com/forum.php? ... p;extra=&page=3

新接的分析case, I was told this tooling cracked in one day, and one day only.

Very serious segregation and high density of twin and coarse boundary carbide are present.
These flaws appeared before (segregation) and right after ingot forging(twin carbide).