Making Sure It Works: The Importance of Testing and Validation

Introduction :

Testing and validation are essential steps in ensuring that any engineering design or product performs exactly as intended. By rigorously checking functionality, reliability and safety, engineers can identify issues early, improve quality and build confidence in the final outcome. Whether developing a new component, system or full-scale product, testing and validation provide the evidence needed to make sure it truly works in the real world.

That is, testing your design to make sure it meets the requirements set out in the Design Specification.
In order to do this effectively, ISO9001 sets out two steps, Design Verification and Design Validation.

Design Verification

Verification is strictly a paper exercise. It starts with taking all the design inputs: specifications, government and industry regulations, knowledge taken from previous designs, and any other information necessary for the design to work. With these requirements in hand you compare to your design outputs: drawings, assembly instructions, test instructions, and electronic design files.

The basic question is ‘does it work on paper?’

In the comparison you are ensuring that each requirement in the inputs is accounted for in the outputs. Is each required test called out in the test instructions, including the correct pass/fail criteria for each test? Are all product acceptance criteria correct? Are all physical characteristics identified in the build instructions?

Verification is a comparison between the outputs and the inputs. Does the available evidence indicate that the design will meet the requirements? The verification could consist of calculations, simulations, prototype evaluation, tests or comparison against samples. 

The output of this verification review is often recorded in a Statement of Compliance document.

This document will list every requirement for the design, identify if the design is compliant or not, and list where this compliance is proven in the documentation.

A sample line may look like this:

The obvious importance in this step is to make sure that the design has not missed addressing any requirements. If requirements are not compliant, meaning the design does not meet a requirement, now is the time to know this and either add or fix the missing requirement.

Design Validation

Validation is similar to verification, except this time you should check the designed product under conditions of actual use. This does not necessarily mean the first production unit, (although it could be). It can also be an engineering model, which some companies use to prove the first run of a complicated new design, or it can be a portion of the design which is different from a previous model, when the design is a modification of an already-proven design.

The basic question now is  ‘does it work in reality?‘

Methods of validation could include simulation techniques, proto-type build and evaluation, comparison to similar proven designs, beta testing, field evaluations, etc. 

Once you decide what method of validation you will use to prove your design, you fully test it to make sure that the product, as designed, will meet all the necessary requirements defined in the Design Specification.

This will often require more testing that will be used on production models. To ensure that all requirements are met, a full set of measurement and tests is done on the validation unit. In some industries this is referred to as a First Article Inspection (FAI). Depending on customer requirements this can be recorded as a standalone document, or an addition to the Statement of Compliance created in the verification step.

A sample line may look like this:

After validation, it is not likely that the full set of tests should be done on every item produced, that depends on factors such as the criticality of the requirement or manufacturing process capability (for example, some safety features might be checked on every production run). A good product validation can help decide which requirements need to be checked on every product, and which do not.
Irrespective of the methods used, the validation activity should be planned, and executed with records maintained as defined in the planning activity.

Computer Aided Design Validation

As mentioned above, sometimes it is possible to validate the test using computer methods. One of the most common methods is called Finite Element Analysis (FE Analysis). 

Using FE analysis, it is possible to take the 3D model of your product (from programmes such as Autodesk Inventor) and apply representative real world loading and forces on the model to see how they bend, move and break. You will not be asked to perform these tests for this unit, but you should be aware of their use for design validation purposes.

Another common computer testing method is Computational Fluid Dynamics (CFD) – this can validate/predict how fluids will move (such as a liquid through a pipe, or airflow over an aircraft wing). However we will not cover this in any more detail in this module.

Verification vs Validation

In summary, each of these steps is important in the design process because they serve two distinct functions. Verification is a theoretical exercise designed to make sure that no requirements are missed in the design, whereas validation is a practical exercise that ensures that the product, as built, will function to meet the requirements. Together, they ensure that the product designed will satisfy the customer needs, as defined in the design specification

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