Understanding Materials

Material properties weigh heavily on end-use applications. The information here should act as a primer behind the 3D printing technologies and raw materials used at BenchRebel. The rabbit hole gets deeper as you explore the science and technology - we are not going to do that to you on this site. Enjoy!

Detailed material properties and design guidelines below.

Flexible Materials
Durable & Tough Materials
Rigid Materials
General Purpose Materials

3D Printing Techologies

Two 3D printing technologies are common and popular - stereolithography and fused deposition modeling. The early focus at BenchRebel is on stereolithography. When comparing these two technologies, its important to note that it is not an apples-to-apples comparison.

Stereolithography (SLA): SLA 3D printing uses ultraviolet light (UV) to cure and chemically bond the polymer resin layers. Material choice is more limited when compared to FDM offerings though SLA products can excel in the fine details, isotropic qualities (see later) and be watertight under pressure. In general, raw materials and hardware are more expensive, and post-processing more specialized.

Fused Deposition Modeling (FDM): FDM 3D printing heats (melts) a thermoplastic filament, deposits the material layer-by-layer, and establishes a physical bond as it cools. Material choice and colors are widely available, including options to print in multiple colors/materials in a single job. FDM is more common with hardware and finishing requirements typically less costly and intensive.

	SLA	FDM
Surface Finish	Excellent	Layer lines more visible
Detail/Resolution	Very high	Moderate
Cost	Higher	Lower
Materials	Photopolymer resins with limited color options - painting and dyeing are common	Thermoplastic filaments with many types and colors

Physical Properties

Note: Isotropy and watertightness are design considerations, not disqualifications. When isotropy and watertightness are unnecessary or accounted for, FDM may be a better, or cheaper, choice.

Isotropy: Isotropic materials maintain strength and stiffness in all directions. In the case of 3D printed products, isotropy is a critical variable when considering a products intended use. The SLA products at BenchRebel are highly isotropic. FDM products, by contrast, are anisotropic due to the shearing risk along the layer plane. Considerations:

• SLA printed products are chemically bonded, making them highly isotropic
• FDM printed parts are anisotropic due to a physical, not chemical, bond between layers, increasing the risk of shear or tear failure between layers under stress

Watertight: The chemical bond between SLA layers also creates a watertight surface, enabling use in rain, on water, and underwater in high-pressure environments without added preparation. FDM products require more careful design consideration if anisotropy or watertightness is a concern, though these factors alone should not discourage the use of the technology.

Tensile Properties

Ultimate Tensile Strength: Maximum stress a material withstands before fracture during tensile testing or performance under tension (stretching or pulling).

Tensile Modulus: Alternatively known as Young's modulus, measures a materials resistance to lengthwise stretching or compression

Elongation at Break: The strain, expressed as a percentage, a material experiences from its original length is subjected to tensile stress until it fractures - a critical data point  when ductility and flexibility are considerations.

Shore hardness: Is an element of soft materials (rubber, plastics, polymers, etc.) and often seen as Shore A or Shore D references. Alternatively, shore hardness is sometimes referred to as Durometer A or D, referencing the durometer used to measure shore hardness.

BenchRebel uses 3 flexible materials. When cured, these materials achieve 40A, 55A, and 80A shore hardness. To compare the three

• 40A is soft and flexible like silicone seals, grips, wearables, etc.
• 55A is pliable like vibration pads, pencil erasers, rubber bands, etc.
• 80A is firm yet flexible like impact pads, boot soles, leather belts, etc.

Flexural Properties

Flexural Strength vs Flexural Modulus: Think maximum load while being bent vs resistance to bending. Flexural strength is the maximum stress a material can withstand before breaking when bending. Flexural modulus measures the material's stiffness or resistance to bending under load, without necessarily reaching failure.

Impact Properties

Notched Izod vs Unnotched: Notched Izod tests simulate real-world flaws, such as a machined notch in a material, to test a material's impact performance at the point of stress and leading to fracture. By contrast, Unnotched Izod measures overall impact resistance when a material is undamaged or pristine.

Gardner Impact Testing: Tests the impact resistance of a plastic, or coating, by dropping a weight from a specified height and noting the amount of energy necessary to cause the material to be cracked or damaged.

Fracture Properties

Work of Fracture: Tests a materials touchness and resistance to crack spread or propagation. High work of fracture means better resistance to crack growth and part failure.

Thermal Properties

Heat Deflection Temperature (HDT): Measures the temperature when a polymer or plastic begins to deform under a load. For example: 122 deg. F @1.8MPa (261 PSI), shows the referenced material will deform at 122 deg. F when subjected to a load of 1.8 megapascals (261 pounds per square inch).