ABS Trouble Shooting - Molded Part Cracking

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Molded Part Cracking

Chemical stress

Fatigue failure

Plated part cracking

Molding Defects
   Silver streaks
   Short shot
   Jetting
   Flow marks
   Color streaks
   Weld lines
   Flash
   Delamination
   Stringiness
   Sink marks
  Warping or twisting

Weathering

Painting Defects
   Pinholes
   Cracks
   Sinking
   Crawling
   Sealing defects

Molded Part Cracking

Cracking of ABS molded parts can be classified as one of the following three typical types in accordance with visual examination of the broken or cracked surface. The corresponding fracture mode constitutes important information for the purposes of cause identification and countermeasure.

Scanning electron microscope photographs

Pictorial representation of fracture surface

The fracture surface has turned white.
Ductile fracture

There are many undulations on a ductile fracture surface and it appears to have a fuzzy texture.

Ductile fractures occur when a part is simply subjected to a force that is larger than the material strength - in other words, when it is simply exposed to a large external force.

The fracture surface has not turned white.
Brittle fracture

Chemical stress cracking is a typical example of brittle fracture. In such a case, there are no undulations on the fracture surface and it takes on a smooth appearance.

Brittle fracture is caused by a combination of a force or stress which is less than the material strength and some other factor (i.e., chemical agents, temperature, paint, plating, state of external force application, etc.).

Clam-shell marking is visible on the fracture surface.
Fatigue failure

Fatigue failure surfaces exhibit a unique clam-shell marking (or conchoidal) pattern.

Simplified Causes and Countermeasures for Different Crack Types

Type of Ductile Failure	Cause	Characteristics and Countermeasures
Ductile fracture	Excessive external force	Whitening of failure or crack surface Elimination of excessive external force

Type of Brittle Failure	Cause	Characteristics and Countermeasures
Chemical stress crack*	Chemical agents and stress	In certain significant cases, the fracture surface exhibits a mirrored finish. Change the chemical agents and/or material.
Fatigue failure	State of external forces and repetitive loading	Clam-shell markings are visible on the fracture surface.** Switch to highly fatigable material
Fracture of painted parts	External force and inferior paint characteristics (for impact and extension)	Eliminate the external force
Fracture of plated parts	External force and inferior plating characteristics (for impact and extension)	Eliminate the external force
Fracture due to deterioration of material properties	External force and deterioration of the molded part's physical properties
Fracture due to deterioration of material properties	Mixing of different materials Deterioration as a result of weathering or light Thermal degradation Thermal degradation in the cylinder	Eliminate the cause of mixing Use materials with good weather resistance Use materials with good thermal properties Ensure that conditions are suitable for molding
Fracture due to usage of materials with poor impact characteristics	External force and low-strength molded parts	Switch to materials with high impact strength
Fracture at low temperatures	External force and a drop in molded part strength	Switch to materials with high impact strength
Creep fracture	Application of loading over an extended period of time	Reduce initial deformation and load Increase the modulus of section Reduce the stress

*: Environmental stress cracking **: Conchoidal pattern

UMG ABS, Ltd accepts no responsibility for the quality or safety of any customer products which use our materials or which have made use of any type of data provided by this company. Customers are requested to independently determine the suitability of our materials for their products. We also request that sufficient attention also be paid to laws, regulations, and industrial rights.