Toughening of Plastics and Its Design

Applied load deforms the molded products of plastic. When the load is further increased, the products are destroyed into the several pieces together with a larger sound or it is greatly deformed by a constant load and a permanent strain remains by unloading. The fracture which forms the several pieces together with the large sound is called as brittle fracture, and the deformation which brings to a permanent strain is called as ductile deformation. On the brittle fracture, the crack propagates with extremely a high speed and it is impossible to prevent the propagation of crack by unloading. On the other hand, on the ductile materials, the increase of plastic strain stops by unloading. Ductility, that is, tough plastics are excellent to use the products at ease compared with brittle plastics.

If molded product of what shape is designed or what kind of material is chosen, is it appropriate to the control of the brittle fracture of it ?. It is necessary to understand the mechanisms of destruction of polymeric materials in order to produce the plastic parts with high confidence about the mechanical properties.

1. Introduction

2. Deformation of solid polymeric materials

2.1 Structure of solid polymers

2.2 Based of deformation of solid materials

2.2.1 Deformation that is dominated by shear deformation

2.2.2 Deformation that is dominated by volume deformation

2.2.3 Stress concentration due to constatint of strain

3. Ductile fracture of polymeric materials that are dominate by shear deformation

3.1 Plastic deformation of crystalline polymers

3.2 Plastic deformation of amorphous glassy polymers

3.3 Softening and necking of polymeric materials

3.4 Orientation hardening

3.5 Ductile fracture

3.5.1 Ductile fracture of thermoplastic polymers

3.5.2 Fracture of thermosetting polymers

3.6 Influence of the rate of deformation on the behaviors for the plastic deformation of polymer

3.7 Ductile fracture by creep road

4. Brittle fracture of polymeric materials that are dominated by volume deformation

4.1 Formation of voids and its unstable expansion

4.2 Unstable expansion of voids due to constraint caused by notch

4.3 Brittle fracture of polymeric materials under constraint of strain

4.3.1 Brittle fracture of amorphous glassy polymers

4.3.2 Brittle fracture of crystalline polymer

4.4 Influence of deformation rate on the fracture behavior

4.5 Brittle fracture of polymer having a notch by creep load

4.6 Comparison with fracture of aluminum alloy

4.7 Fracture mechanics and application to the polymer materials of it

5. Toughening by adjustment of designs

5.1 Constraint of strain on the structure and the stability of deformation

5.2 Strength design of amorphous glassy polymers

5.2.1 Estimation of true stress-strain curve of PC

5.2.2 Estimation of fracture condition of PCM

5.2.3 Predication of toughness of structure of PC under various boundary conditions

5.2.3.1 Effect of radius of notch tip

5.2.3.2 Effect of thickness of ligament

5.2.3.3 Effect of width of specimen

5.3 Strength design of crystalline polymers

5.3.1 Estimation of true stress-strain curve and volume strain due to voids of POM

5.3.2 Estimation of fracture condition of POM

5.3.3 Predication of toughness of structure of POM under variousboundary conditions

5.3.3.1 Effect of radius of notch tip

5.3.3.2 Effect of thickness of ligament

5.4 Evaluation method of toughness of polymer and boundary condition

6. Toughening by a adjustment of fine structures

6.1 Improvement of strength of craze by raising molecular weight

6.2 Improvement to polymers having high craze strength with low viscosity by narrowing width of molecular

weight distribution

6.3 Improvement of craze strength by decrease of defect on stereoregularity

6.4 Depression of brittle fracture by increasing the ration of strength of craze to yield stress due to

copolymerization

7. Toughening by the release of constraint of strain

7.1 Relaxation of bulk modulus and release of constraint strain by void

7.1.1 Effect of dispersion state on instability of expansion of void

7.1.2 Estimation of toughness of polymer alloy by nonlinear analysis that uses Gurson model

7.1.3 Estimation of toughness of polymer alloy by modified Gurson model

7.2 Factors influencing the efficiency of the toughening by elastomer blend

7.2.1 Improvement of toughness by lowering strength of dispersed phase

7.2.2 Improvement of toughness by appropriating the orientation hardening rate

7.2.3 Improvement of toughness by making orientation hardening rate appropriate

7.2.3.1 Adjustment of the rate of orientation hardening by partial crosslinking

7.2.3.2 Adjustment of the rate of orientation hardening by crystallization condition

7.2.4 Improvement of toughness by making compatibility of elastomeric moderation

7.2.5 Influence of elastomer orientation of dispersed phase on toughness due to flow

7.2.6 Control of the brittle fracture due to the surface deterioration y the mixture of elastomer

7.2.6 Other Attempt to relax bulk modulus

8. Strength Design of Plastic Composite Material with High Rigidity and Toughness

8.1 Toughening by blend of inorganic particles

8.2 Toughening by blend of fibers

8.2.1 Case of strong adhesive strength on the interface

8.2.2 Case of flaking off in interface by appropriate stress

8.2.2.1 Effect of the strength of flaking off on the Toughness

8.2.2.2 Effect of the aspect ratio of fiber on the toughness

8.2.2.3 Effect of the contraction force of polymer on the toughness

8.2.3 Example of the improvement of the toughness by the adjustment of the interface strength

8.2.3.1 Toughening of PC blended with glass fiber by the low molecular weight polyethylene

8.2.3.2 Improvement of both elastic modulus and toughness of PLA by aramid fiber

9 Conclusions