Quick Selection Test - The Wedge Method
The 3Dresyns® Structured Mechanical Screening Protocol (SMSP) is a structured, printer-native methodology intended to obtain a practical comparative mechanical fingerprint of a photopolymer system on the user's own equipment.
It translates printed wedge behaviour into two primary empirical readouts: how much the wedge bends, used to compare rigidity versus flexibility, and where it breaks, used to compare toughness versus brittleness under flexion within the SMSP geometry and test conditions.
SMSP complements the Engineering Resin Selection Tool by adding a fast empirical confirmation step requiring minimal setup and no dedicated mechanical testing instrument.
SMSP is a screening methodology, not a standardized mechanical property test. It does not directly determine tensile strength, Young's modulus, flexural strength, elongation at break or other formal mechanical properties.
For broader calibration, troubleshooting and engineering documentation, use the consolidated 3Dresyns® Photopolymer Engineering System and Resources.
Download the STL
- The Wedge (STL): Download
If you need the full calibration pack, including CRT-related files, email info@3Dresyns.com.
What SMSP Screens
- Rigidity vs flexibility through comparative low-load bending response.
- Toughness vs brittleness through comparative fracture behaviour under high flexural loading of the wedge.
- Peeling / separation behaviour as a qualitative process-stability indicator.
- Large-area stability when printed at large footprint, including indications related to levelling and exposure distribution.
These readouts are intended for comparative engineering screening within the SMSP workflow. They should not be interpreted as direct measurements of standardized mechanical properties.
Two Complementary Print Modes
SMSP-A: Flat mode (large-area / process stability)
Use flat mode when the target parts cover large cross-sections or when screening levelling, adhesion behaviour and vat-wide exposure consistency is relevant.
- Print flat on the build platform, without supports.
- Scale to cover a representative build-plate area when relevant.
- Use for comparative screening of adhesion stability, peel behaviour and exposure uniformity across the vat.
SMSP-B: Vertical mode (cantilever mechanical fingerprint)
Use vertical mode to obtain the primary comparative flexural readouts, including rigidity threshold and break thickness, with a cantilever-type loading behaviour.
- Print the wedge in vertical orientation, without supports.
- Use for comparative screening of rigidity versus flexibility and toughness versus brittleness under flexion.
Printing Instructions - Recommended Starting Point
- Bottom adhesion layers: 2 layers. Use your established bottom exposure approach.
- Standard layers: start with the exposure time needed to cure 1.5 layers.
- If available: record printer light power at 405 nm in mW/cm² for improved comparison and traceability.
If removal is difficult or the wedge cracks during removal, do not force it. Print flat using SMSP-A and/or reduce bottom exposure. Excessive adhesion may indicate bottom overexposure rather than superior mechanical behaviour.
For comparative use, retain the relevant printing and post-processing conditions together with the SMSP observations.
Comparability Conditions
Compare like with like
SMSP is most informative when candidate materials or processing conditions are evaluated under controlled and documented conditions.
When comparing results, record the relevant variables available to you, including:
- material and material version;
- printer model;
- printing orientation;
- layer height;
- exposure conditions;
- bottom-layer conditions;
- printer light power where available;
- cleaning conditions;
- post-curing conditions;
- test state; and
- rigidity threshold and break thickness.
Changes in printing, cleaning, post-curing or test conditions can affect wedge behaviour. Results generated under materially different conditions should therefore not be treated as directly equivalent.
SMSP Readouts
Readout 1: Rigidity threshold (low-load bending)
- Hold the wedge vertically.
- Apply gentle lateral force at the tip.
- Identify the thickness in mm at which bending becomes negligible.
Rigidity threshold is the practical transition from compliant to rigid behaviour for the selected SMSP geometry, material state and test conditions.
Use it as a comparative SMSP indicator rather than as a direct measurement of Young's modulus or another standardized stiffness property.
Readout 2: Break thickness (high-load fracture)
- Apply stronger lateral force until fracture occurs.
- Measure the thickness in mm at the fracture point.
SMSP interpretation rule: within comparable test conditions, lower break thickness, meaning fracture closer to the tip, typically indicates greater practical resistance to flexural fracture in the wedge test. Higher break thickness indicates comparatively more brittle behaviour.
Break thickness is an empirical SMSP readout. It is not a direct standardized measurement of fracture toughness, impact strength or flexural strength.
Graphical Interpretation
A) Low-load bending: rigidity vs flexibility
Apply a gentle, controlled lateral force at the tip. Compare the wedge shape after bending. Greater curvature indicates greater flexibility within the SMSP wedge geometry and test conditions.
- Rigid: minimal curvature; bending concentrates only at the very tip.
- Rigid but brittle: appears rigid at low load but tends to fracture earlier under the higher-load SMSP step.
- Semi-rigid: curvature initiates near the upper region.
- Flexible: curvature initiates around mid-height.
- Elastic: curvature initiates low, near the base, with recovery after unloading.
Rigidity readout: record the thickness at which bending becomes negligible. Within comparable SMSP conditions, a lower rigidity threshold typically indicates comparatively more rigid behaviour.
B) High-load fracture: toughness vs brittleness
Apply stronger lateral force until fracture occurs. Within comparable SMSP conditions, materials showing fracture only in thinner wedge regions are interpreted as more resistant to flexural fracture than materials breaking in thicker regions.
- Tough: break occurs very close to the tip, in a thin section.
- Balanced: break occurs at an intermediate thickness.
- Brittle: break occurs farther from the tip, in a thicker section.
SMSP toughness readout: record the thickness at fracture. Lower break thickness is interpreted within this methodology as comparatively tougher behaviour under the SMSP flexural loading condition.
Mechanical Interpretation Matrix
| Rigidity threshold | Break thickness | Practical SMSP behaviour | Selection direction |
|---|---|---|---|
| Low | High | Rigid but brittle | Consider a tougher material family |
| High | High | Flexible but comparatively weak under the SMSP fracture step | Consider a tougher / stronger material family |
| Low | Low | Rigid and tough within the SMSP comparison | Potential structural candidate for further validation |
| High | Low | Flexible and tough within the SMSP comparison | Potential compliant / impact-tolerant candidate for further validation |
Mobile: scroll horizontally to view all columns. The first column remains visible while scrolling.
Important: the matrix is a comparative selection aid within SMSP. Terms such as rigid, flexible, tough and brittle describe the empirical wedge response and do not replace standardized quantitative mechanical properties.
Interpretation Limits
What SMSP does not measure directly
SMSP is designed for rapid comparative material and workflow screening. It does not directly determine standardized quantitative values such as:
- tensile strength;
- Young's modulus;
- elongation at break;
- flexural strength;
- impact strength;
- fracture toughness; or
- other formal mechanical properties obtained through dedicated test methods.
The manual bending and fracture steps are empirical. Operator technique and other uncontrolled variables may affect the observed result.
For this reason, SMSP is most useful as a comparative screening methodology when geometry, printing conditions, material conditioning, post-processing and test procedure are kept as consistent as practical.
SMSP versus Standardized Mechanical Testing
SMSP and standardized mechanical testing serve different purposes.
- SMSP: rapid, printer-native, comparative empirical screening.
- Standardized mechanical testing: quantitative measurement using defined specimens, equipment, test procedures and conditions.
SMSP can help identify promising material families or processing conditions before investing in more extensive characterization.
Where formal mechanical values, contractual acceptance criteria, engineering design data or application qualification are required, the relevant quantitative testing should be performed separately.
SMSP versus Acceptance Criteria
A rigidity threshold, break thickness or qualitative SMSP classification is not automatically a contractual material specification or acceptance criterion.
Where an SMSP readout is intentionally used as a project-specific acceptance criterion, the applicable project documentation should define the relevant geometry, material state, printing conditions, processing conditions, procedure and acceptance range.
Integration into the 3Dresyns® Workflow
- Define requirements: application, geometry, load mode, target behaviour and workflow constraints.
- Select by engineering criteria: property targets, structural behaviour and material family.
- Control curing: use CRT and calibration logic where dimensional or mechanical consistency matters.
- Confirm with SMSP: obtain a comparative printer-native readout of printed wedge behaviour.
- Characterize where necessary: use appropriate quantitative testing when formal mechanical data are required.
- Validate application performance: final qualification must be performed under application-specific conditions.
If you share your rigidity threshold and break thickness measurements together with the relevant printer and processing information, 3Dresyns® can use the data to support material-family selection. Contact info@3Dresyns.com.
Integration with Advanced Validation & Characterization
SMSP can be used as an early comparative screening step before more detailed characterization.
Where quantitative mechanical, thermal, rheological, microstructural or other technical evidence is required, the project may progress to Advanced Validation & Characterization.
SMSP results and formal characterization results should retain their respective test context and should not be treated as interchangeable.
Application Validation
Selection of a material using SMSP does not establish that the material or printed part is suitable for every final application.
Final performance may depend on geometry, load case, printer, exposure, cleaning, post-curing, environmental conditions and other application-specific variables.
The customer remains responsible for validating the final printed part and manufacturing process under its intended use conditions.
For regulated applications, SMSP does not constitute regulatory certification, conformity assessment, medical-device validation, food-contact authorization, pharmaceutical qualification or other regulatory approval.
Reporting SMSP Results
For meaningful comparison and technical communication, record the SMSP result together with the relevant test context.
A useful SMSP record may include:
- material identification;
- printer model;
- SMSP-A or SMSP-B mode;
- layer height;
- exposure conditions;
- light power where available;
- cleaning conditions;
- post-curing conditions;
- rigidity threshold;
- break thickness;
- observed peeling or separation behaviour where relevant;
- large-area observations where relevant; and
- any significant deviation from the usual SMSP procedure.
This contextual information helps distinguish a material-related difference from a difference caused by printing or processing conditions.