Mechanical Testing Services Information
Mechanical testing services is a comprehensive term that refers to a range of activities involving the determination of mechanical properties and behavior of material, structures, and machines. In general, testing involves creating a physical stimulus and measuring the reaction. This input may be either dynamic or static and can be at a small point load, multiple points of loading, or distributed across a larger area.
Mechanical testing is the process of physically applying a stimulus to a mechanical system. These stimuli can be displacements, heat, forces, pressures, or other physical stress that may be placed on the object being tested. Mechanical testing can be used to verify the key performance attributes of the material, part, or complete mechanical system in question. When testing focuses on properties of a material, independent of size or shape, special test pieces or “coupons” are created to mate with the test equipment being used.
Types of Services
Mechanical testing services can be any or many of a long list of tests manufacturers need to either verify the robustness of their design or to meet certifications and standards required to take a product to market. A mechanical testing service can provide information in many forms and varying depth and detail. Different testing capabilities include the following:
- Component/product testing is characterized by inspection or testing services for existing in-service or newly fabricated products using techniques such as non-destructive testing (NDT), visual inspection, chemical analysis, or structural material testing.
- Component/product comparisons services offer product comparison testing services. The test can compare current and next generation products within a company or similar products from different companies.
- Consulting and training services provide consultation related to testing, inspection, test methods, or techniques, regulations, regulatory impact, and/or registration process.
- Engineering verification testing includes basic functional tests, parametric measurements, and specification verification.
- Evaluation and analysis: The provider offers evaluation and analysis of products.
- In-process in-line testing tests the product on-site in its functional environment.
- Performance testing typically evaluates the compliance of a system or component with specified performance requirements.
- Reliability and robustness: The testing facility offers reliability or robustness testing. Generally, reliability or robustness is a measure of a system's vulnerability to potentially corrupting influences. This has a special importance when components of a system fail.
- Test development service may be offered in the form of customized test development services to test unique or proprietary parts.
- Test fixtures and equipment services allow the test facility to build their own testing fixtures for specific applications. Some test providers have very well equipped and capable machine shops, while others have partnered with local tool makers to ensure responsive turnaround.
- Test panel and sample prep refers to the design and fabrication of test sample or test panels for testing or simulation of products such as paints, coating, lubricants, or materials where testing of a complete part or product is unproductive or not feasible.
The following paragraphs list common mechanical tests with descriptions of what they are and how they are carried out.
- Tensile and compressive: Tensile testing is the most common test for materials and products. Characterizing and reporting tensile test properties is a basic need in most labs from quality control to R & D. In compression testing, a material or product is squeezed or compressed by aligned opposing loads or forces. Compression testing can be performed on materials for a variety of purposes. Depending on the material type, compressive properties can be dramatically different than tensile properties. Compression tests can be performed on static or dynamic systems. Static systems are usually the system of choice due to the larger displacement offered, and the relatively slow speed of the system for safety purposes.
- Adhesion (bond/peel): Adhesion, bond, or peel tests are used to evaluate joints, adhesives, coatings, or adhesive tape adherence, bond strength, or peel strength. ASTM D-952 defines bond strength as the tensile stress required to rupture a bond formed by an adhesive between two metal blocks. Adhesion is the state in which two surfaces are held together by interfacial forces, which may consist of valence forces, interlocking action, or both. Adhesion is one of the most important properties of a coating (thin film, paint, plating, or other systems). Peel strength is commonly used to characterize adhesive tapes and coatings.
- Ductility: Ductility is the ability to undergo plastic deformation in tension or bending before fracturing. The ductility of metals or ductile plastic materials is typically evaluated in tensile tests. The degree of permanent plastic deformation or strain in terms of percent elongation or percent reduction in area provides a measure of ductility.
- Creep/stress relaxation tests characterize material performance under constant strain or stress conditions, usually at elevated temperatures. These tests evaluate creep, stress relaxation, or stress rupture. These tests can provide important information about material or component properties under longer term conditions. Creep or stress rupture tests are important in evaluating high temperature aerospace or jet engine component materials. Stress relaxation tests are usually performed under constant strain conditions. This usually involves going to a specific load or strain point, then holding the strain value. The resulting decrease in load or stress values is recorded over time. Creep tests are usually performed under constant load or stress conditions. These types of tests are performed by going to a load or stress point, then holding the load or stress value. The resulting increase in strain is recorded over time. Short- and medium-term creep and stress relaxation testing can be performed on static or dynamic systems.
- Drop/shock or shock testing: Information obtained during shock testing can improve the survivability of products as well as verify that they will perform properly in service. The purpose of shock testing is to determine the mechanical fragility level of a product, that is, the deceleration level where damage is likely to occur. This information is most useful for package design and testing purposes, although it is also very important for product analysis for the in-use environment as well. In aerospace applications, these tests are often pyrotechnic separation, or pyroshock, events associated with launch vehicle applications. Shock testing involves shaping or programming the nature of a shock input pulse in order to characterize both the velocity change and the acceleration response of a typical product. This is important because products fail in distinct ways depending primarily on the nature of the shock input. Normally, this involves programming short duration half-sine pulses and longer duration trapezoidal shaped shock pulses into a product.
- Impact strength tests are also considered shock tests. Impact strength is determined through Charpy or Izod pendulum impact tests, dead weight drop (Gardener/Gardner) tests and tensile shock load tests.
- Fatigue/cyclic tests may also be called dynamic tests. Fatigue testers measure the fatigue resistance, or resistance to failure, of materials under controlled conditions of cyclic deformation. Failure of the test piece is the result of crack growth and the design of the machine. The cyclic load may be applied using a tensile tester with cycling capability, rotating beam tester, or vibration tester.
- Friction/wear: Friction testers determine the coefficient of friction or the friction force, the resisting force tangential to the interface between two bodies when, under the action of an external force, one body moves or tends to move relative to the other. Wear testers evaluate the amount or type of wear (material removal or transfer) that occurs between two surfaces under wet, dry, lubricated conditions or with abrasive particles. A pin on disc tester is a common machine used for wear tests. An applied load is transmitted through the pin to a rotating disc. The pin and disc are made of or coated with the materials to be evaluated.
- Flexure/bending: Flexure or flex tests are used to evaluate the strength of brittle, fibrous, anisotropic, or low ductility materials, including ceramics, composites, cast irons, highly loaded plastics, wood, concrete, and refractories. Flexure testing consists of applying a load to a beam of the test material or sample, which is supported at both ends. Flexural strength, fiber strength, or modulus of rupture (MOR) is reported in these tests. Material properties can vary based upon the direction that stress is applied. For instance, concrete is very strong in compression, but weak in tension. Depending on the material rigidity, stiffness, or specifications, either a three-point or four-point configuration is used. Four-point bend tests provide a known, uniform stress between the two central points. Test results are included as long as the sample breaks between the two central points. The term bend test is sometimes used to describe flexure tests, although bend or bending test types vary greatly and can be much different than a simple beam loading test. Bend test specifications are often particular to specific materials.
- Hydrostatic/burst testers apply an internal pressure and/or flow using a fluid (gas or liquid) to evaluate fittings, pipe, tubing, vessel, cylinders, as well as other hydraulic, pneumatic, or process components. The tests may determine what flows or pressure a component can withstand before catastrophic failure occurs or leaks develop.
- Impact toughness: Impact tests measure the energy absorbed by the specimen before it breaks, a quantity composed of several energy contributions, including energy absorbed by the impact machine through vibrations after initial contact with the specimen and loss in pendulum energy (in pendulum impact tests) when the hammer strikes the specimen as well as the total energy consumed by specimen deformation and fracture. Although it is very difficult to measure many of the individual energy contributions, impact tests are a valuable comparative test method.
- Shear/torsion: The shear strength is defined as the maximum stress that a material can withstand before failure in shear. In a planar shear test, opposing forces are applied parallel to the cross-sectional area under test. Torsion tests also provide an indication of shear properties. Torsion tests evaluate materials or products under twisting loads or opposing radial forces. Data from torsion test is used to construct a stress-strain diagram and to determine elastic limit torsional modulus of elasticity, modulus of rupture in torsion, and torsional strength.
- Texture analysis: Texture analysis is primarily concerned with the evaluation of mechanical characteristics where a material is subjected to a controlled force from which a deformation curve of its response is generated. Texture analysis is an integral part of the production chain, generating benefits throughout, from research and development to process optimization and production. Key fundamental characteristics that affect finished product texture quality are identified throughout the initial stages of development after which they may be selected for at-line process control measurements. Common characteristics analyzed include hardness, cohesiveness, elasticity, adhesiveness, and viscosity. Secondary characteristics include brittleness, chewiness, and gumminess.
- Vibration test systems are used to evaluate materials, products, and packages for design purposes as well as to simulate the vibration effects of product transportation. Vibration testing consists of an oscillating load.
Mechanical testing services cover a broad range of industries including aerospace/avionics, appliances, automotive, building and construction, battery and energy products and coatings. Mechanical testing is an important research and development tool for electrical, electronics, marine, power generation, paper, packaging, RF products, and semiconductor manufacturers. Food, drug, health care, and medical products have more stringent requirements and standards and are likely to have fewer options in mechanical testing service providers.
When selecting a mechanical testing service, testing standards and certifications are an important factor as are the physical capacity of testing equipment in size (volume X by Y by Z) and weight of the test piece and loading capabilities of the test machines. There are “soft” considerations as well. Proximity to the manufacturer has many benefits in terms of shipping the test piece adherence to schedule and engineering involvement in the test. Sometimes lower-cost options located at greater distances have soft costs that add up and need to be factored into final selection decisions.