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Torsten’s Training Tips: Mechanical Material Behavior

by Torsten Kruse

Injection molding is a widespread manufacturing process used to create various everyday items, ranging from pipette tips to car bumpers, using different polymer materials. These parts can be made from either pure, unfilled polymers or those that are enhanced with reinforcements and additives. It’s crucial for designers of these parts to understand the mechanical behaviors and properties of various polymers to select the most suitable one for different applications.

Mechanical Material Behavior

There are two primary types of polymer behavior: isotropic and anisotropic. The term “isotropic”, coming from the Greek word “isos”, signifies uniform material properties.

On the other hand, “anisotropic”, derived from “anisos”, means the properties are not uniform or consistent. The suffix “tropic”, from “tropos”, translates to “way” or “direction”.

Typically, isotropic behavior is observed in pure, unfilled materials, while anisotropic behavior is seen in materials that are reinforced with fibers or contain additives that impart directional characteristics.

In the context of molded parts, stress refers to the internal pressure caused by an external load. Molded parts can experience various types of stress, including tension, compression, shear, torsion, or a mix of these. Strain is how the material reacts to this stress or load, leading to physical changes like stretching or compressing the part. Factors like flow-induced stress, residual stress from molding, and thermal stress can affect how the part shrinks or warps.

Understanding that molded-in stress, along with the material’s properties, plays a key role in determining the shrinkage and warping of a part is vital. This knowledge is fundamental to the successful design of both the part and the mold, particularly when working with polymers.




Kruse Analysis, Inc. has been providing CAE simulation services to the plastic injection molding industry since 1995. By using advanced Moldex3D technology, Kruse helps customers troubleshoot from product design to development, optimize design patterns, shorten time-to-market, and maximize product return on investment (ROI). For more information, visit

Kruse Training, Inc. offers a state-of-the-art online knowledge and training solution that use 3D process simulation technology to demonstrate cause and effect of molding behavior. This interactive training program illustrates how “The Circle of Knowledge” between the part designer, mold designer, and process engineers works in the real world of plastic mold and design. For more information, visit

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