Materials properties, impact resistance

Intended to improve physical properties, reinforcements enhance the dimensional stability of materials, increase impact resistance, and improve tensile strength. The distinction between fillers and reinforcements is sometimes vague. Classification according to use. 

Regarding the properties required of the solidified materials in 2D printing, the most important properties are generally related to thin material layers, such as color, adhesion to the substrate, hghtfastness, and scratch resistance, whereas in 3D printing, the most important properties are generally related to the bulk material mechanical and thermomechanical properties, for example tensile and flexural properties, impact resistance, and Glass Transition Temperature (Tg). 

Nature of the Continuous Phase. Impact resistance is a function of the intrinsic properties of the polymer forming the continuous phase, especially its molecular weight (I, 2). This is summarized in Table I for binary PS-PI blends and in Table II for ternary PS-PI-Cop blends. Table I shows that, for a given blend, increase in molecular weight of PS forming the continuous phase of the material increases impact resistance. The same observation can be made from Table II for a ternary PS-PI-Cop blend. 

If the above statements are correct, the additive should not affect most mechanical properties. Impact resistance may be an exception to some degree because it is sensitive to any imperfections in the material, and incompatible material may cause formation of such imperfections. 

Styrene—acrylonitrile (SAN) copolymers [9003-54-7] have superior properties to polystyrene in the areas of toughness, rigidity, and chemical and thermal resistance (2), and, consequendy, many commercial appHcations for them have developed. These optically clear materials containing between 15 and 35% AN can be readily processed by extmsion and injection mol ding, but they lack real impact resistance. 

Mechanical properties of mbber-modifted epoxy resins depend on the extent of mbber-phase separation and on the morphological features of the mbber phase. Dissolved mbber causes plastic deformation and necking at low strains, but does not result in impact toughening. The presence of mbber particles is a necessary but not sufficient condition for achieving impact resistance. Optimum properties are obtained with materials comprising both dissolved and phase-separated mbber (305). 

T and are the glass-transition temperatures in K of the homopolymers and are the weight fractions of the comonomers (49). Because the glass-transition temperature is directly related to many other material properties, changes in T by copolymerization cause changes in other properties too. Polymer properties that depend on the glass-transition temperature include physical state, rate of thermal expansion, thermal properties, torsional modulus, refractive index, dissipation factor, brittle impact resistance, flow and heat distortion properties, and minimum film-forming temperature of polymer latex... 

The thermoplastic polyamide elastomers may be considered as premium grade materials available in a wide range of hardness values with, in some instances, very good heat resistance. Particular properties of interest are the flexibility and impact resistance at low temperatures and the good dynamic properties and related resilience, hysteresis and alternating flexural properties. 

Typical applications for nylon include small gears, bearings, bushes, sprockets, housings for power tools, terminal blocks and slide rollers. An important design consideration is that nylon absorbs moisture which can affect its properties and dimensional stability. Glass reinforcement reduces this problem and produces an extremely strong, impact resistant material. Another major application of nylon is in fibres which are notoriously strong. The density of nylon is about 1100 kg/m. ... 

The toughness of a material is a design driver in many structures subjected to impact loading. For those materials that must function under a wide range of temperatures, the temperature dependence of the various material properties is often of primary concern. Other structures are subjected to wear or corrosion, so the resistance of a material to those attacks is an important part of the material choice. Thermal and electrical conductivity can be design drivers for some applications, so materials with proper ranges of behavior for those factors must be chosen. Similarly, the acoustical and thermal insulation characteristics of materials often dictate the choice of materials. 

Heterogeneous compatible blends of preformed elastomers and brittle plastics are also an important route for the development of blends of enhanced performance with respect to crack or impact resistance. Polycarbonate blends with preformed rubber particles of different sizes have been used to provide an insight into the impact properties and the fracture modes of these toughened materials. Izod impact strength of the blends having 5-7.5 wt% of rubber particles exhibits best overall product performance over a wide range temperature (RT to -40°C) [151-154]. 

The next step in the design procedure is to select the materials. The considerations are the physical properties, tensile and compressive strength, impact properties, temperature resistance, differential expansion environmental resistance, stiffness, and the dynamic properties. In this example, the only factor of major concern is the long-term stiffness since this is a statically loaded product with minimum heat and environmental exposure. While some degree of impact strength is desirable to take occasional abuse, it is not really subjected to any significant impacts. 

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