Yield Stress Determination – Accredited Testing for Material Yielding and Proof Strength Across Global Industries
Our internationally accredited laboratory delivers a specialist yield stress determination service that provides manufacturers, engineers and materials scientists worldwide with the precise, traceable data they need to identify the transition from elastic to plastic behaviour in metals, polymers and composites. Every test is performed within the rigorous framework of ISO/IEC 17025, and each report bearing the ILAC mark is unconditionally accepted by regulatory authorities, notified bodies and supply‑chain partners in all major economies. The determination of yield stress is a cornerstone of structural design, quantifying the stress at which a material begins to deform permanently. For ductile metals that exhibit a distinct yield point, we measure the upper and lower yield strengths; for materials without a clear discontinuity, we determine the proof stress, typically the 0.2 % offset yield strength. By employing calibrated electromechanical and servo‑hydraulic test frames, precision extensometers and environmental chambers, we deliver the legally robust, defensible data that underpin material certification, finite‑element modelling and compliance with the relevant ISO, ASTM, EN and customer‑specific standards.
Product Samples We Regularly Subject to Yield Stress Determination
Our testing machines accommodate specimens ranging from fine wires to heavy structural sections. The following categories represent the most frequently tested items:
- Metallic materials and alloys – hot‑rolled and cold‑formed steels, stainless steels, aluminium, copper, titanium and nickel‑base alloys supplied as plates, sheets, bars, forgings and castings
- Welded joints and heat‑affected zones – cross‑weld and all‑weld‑metal specimens used to verify that the weldment meets the minimum yield strength requirements of the base material
- Plastics and polymer composites – injection‑moulded thermoplastics, thermosetting resins, short‑fibre and continuous‑fibre reinforced laminates where the yield or the offset‑yield behaviour governs the load‑bearing capacity
- Rubber and elastomeric components – sheets, O‑rings and gaskets for which the stress at a defined elongation is used as the practical yield criterion
- Additively manufactured and powder‑metallurgy parts – laser‑sintered and binder‑jetted alloys where the yield stress must be validated against the design allowables
- Fasteners, bolts and threaded components – hexagon bolts, studs and screws for which the proof load and the yield‑strength ratio are mandatory certification parameters
Metallic Materials – Yield Stress Determination According to ISO 6892‑1 and ASTM E8
- Determination of upper and lower yield strengths (ReH and ReL) and the 0.2 % proof strength (Rp0.2) according to ISO 6892‑1 (Metallic materials – Tensile testing – Part 1: Method of test at room temperature) and ASTM E8: a proportional tensile specimen is machined and loaded at a controlled strain rate until well past the yield region. For materials that exhibit a yield‑point elongation, the upper yield strength (the stress at the first peak) and the lower yield strength (the minimum stress during the plateau) are reported. For continuous‑yielding alloys, the 0.2 % offset yield strength is determined from the stress‑strain curve. This yield stress determination is the primary parameter for structural steel design according to the Eurocodes and the AISC specifications, and it directly supports the issue of inspection certificates according to EN 10204.
- Hot‑tensile yield strength at elevated temperatures according to ISO 6892‑2: specimens are heated in a three‑zone furnace with an argon or vacuum atmosphere, and the proof strength at the service temperature – up to 1 200 °C – is reported, providing the data required for the design of power‑plant components, turbine blades and pressure vessels operating in the creep range.
- Compression yield stress of metallic materials according to ASTM E9: a cylindrical specimen is compressed between two hardened platens, and the compressive 0.2 % proof strength is determined, which is essential for the bearing, forging and machine‑frame applications where the material is predominantly loaded in compression.
- Yield stress of reinforcing steel (rebar) according to ISO 15630‑1: full‑section bars are tested to determine the characteristic yield strength Re and the ratio of the tensile strength to the yield strength, which are mandatory for the conformity assessment of the reinforcement for concrete structures.
- Proof load testing of fasteners according to ISO 898‑1 and ASTM F606: a bolt or a screw is loaded to the specified proof stress and held for a defined time; the absence of any permanent elongation beyond the allowable limit certifies that the fastener meets the yield‑strength requirement for its property class.
Plastics, Polymers and Composites – Yield Stress Determination According to ISO 527 and ASTM D638
- Determination of the tensile yield stress and the strain at yield of unreinforced and reinforced plastics according to ISO 527‑1 (Plastics – Determination of tensile properties) and ASTM D638: dumbbell‑shaped specimens are injection‑moulded or machined from a sheet and tested at a constant crosshead speed. The stress at the first point where an increase in strain occurs without an increase in stress – the yield stress – and the nominal strain at yield are reported. For materials that do not exhibit a clear yield point, the stress at a defined offset strain, typically 0.2 %, is used. This yield stress determination distinguishes ductile thermoplastics such as polycarbonate and polyamide from brittle grades and provides the design‑limit data for plastic components subjected to short‑term mechanical loads.
- Compressive yield stress of rigid plastics and polymer composites according to ISO 604 and ASTM D695: a cylindrical or prismatic specimen is compressed, and the compressive yield stress and the compressive modulus are reported, supporting the design of plastic pillars, spacers and structural insulators.
- Flexural yield strength of fibre‑reinforced laminates according to ISO 14125 and ASTM D790: the stress at which the outer fibre of the laminate reaches the yield or the defined offset strain is determined from a three‑point or a four‑point bending test, providing the data for the design of composite panels, wind‑turbine blades and aerospace secondary structures.
- Influence of the temperature and the strain rate on the yield stress of polymers: the yield stress is measured at several temperatures – from -40 °C to +120 °C – and at several test speeds, and the dependence of the yield behaviour on the thermal and the viscoelastic conditions is reported, enabling the engineer to predict the performance of the plastic part under the crash, the impact and the high‑temperature service.
Yield Stress Determination for Specialised Materials and Environmental Conditions
- Yield stress of elastomers and rubber according to ISO 37 (Rubber, vulcanized or thermoplastic – Determination of tensile stress‑strain properties): the stress at a defined elongation – for example, 100 %, 200 % or 300 % modulus – is used as the practical yield criterion, and the data are reported for the quality control and the specification of the rubber compounds.
- Yield stress of additively manufactured metallic components: specimens built by laser powder‑bed fusion or electron‑beam melting are tested in the as‑built, stress‑relieved and hot‑isostatically‑pressed conditions, and the yield strength is compared with the wrought‑alloy specification, supporting the qualification of the printed parts for the aerospace and the medical‑device applications.
- Biaxial and plane‑strain yield stress determination for sheet metal forming: the biaxial yield stress and the forming‑limit curve are measured by the hydraulic bulge test or by the cruciform‑specimen testing, providing the advanced plasticity data that the automotive‑stamping and the beverage‑can manufacturers use to simulate the deep‑drawing and the stretch‑forming processes.
- Yield stress after environmental exposure – hydrogen, sour‑gas and stress‑corrosion conditions: the specimen is exposed to the hydrogen‑charging, the sour brine or the corrosive medium, and the retained yield strength is measured, supporting the material selection for the oil‑and‑gas and the marine applications.
Report Acceptance and Global Regulatory Compliance
All measurements performed within our yield stress determination service are executed under the fully accredited scope of our ISO/IEC 17025 quality management system. Each test report that carries the ILAC mark is therefore automatically recognised by regulatory authorities, notified bodies, customs offices and supply‑chain partners in all major economies. For metal producers, plastics compounders, composite fabricators and component manufacturers anywhere in the world, the report constitutes legally robust, internationally accepted evidence that the yield strength, the proof stress and the related plastic‑flow parameters have been determined in accordance with the applicable ISO, ASTM, EN and customer‑specified methods. The documentation can be directly used to support CE marking, the issue of inspection certificates according to EN 10204 or equivalent national standards, the compilation of technical files for type‑examination, and the resolution of commercial and technical disputes concerning the onset of permanent deformation in any material.
