destructive testing are defined as those
tests that are made to a material through the use of tools or machines, which
produce an irreversible alteration of their chemical composition or dimensional
geometry.
destructive testing are performed on adhesive or adhesive joints
that have 4 main objectives:
·
Get the features and mechanical properties of the adhesive.
·
Made comparative between different adhesives.
·
Check the conditions of application as well as adhesives and
preparation of substrates or adherents.
·
Simulate the ageing conditions of the adhesive bonding during his
lifetime, in order to predict their behavior.
Due that the adhesive process is consider a special process, it is
advisable or necessary, depending on the requirements of the bonded joint, a
series of specimens at the same time it makes application of the adhesive, in
order to check the environmental conditions, surface preparation and product set
of the adhesive system (primers, activators and adhesives or glues). The number
and frequency of performance of these destructive testings are determined by
the degree of safety or dangers of the adhesive bonding.
During the definition and implementation of the specimens to be
used in destructive testing, it must be taken into account the following
points:
·
The material of the specimens must be the same as the real
material of the substrates of the bonded joint.
·
The thickness of the specimen must be as close to the actual
thickness of the substrates of the real bonded joint.
·
The thickness of the adhesive must be the same as the thickness of
the real bonded joint.
·
Surface preparation must be the same, both in media conditions and
products used.
·
You must apply the same system of adhesive, activator, primer as
in the specimens as in the real bonded joint.
Once the specimen has been made, it is then the destructive
testing which verifies the following main parameters:
·
Type of fracture - adhesion, cohesion, substrate, mixed or
boundary layer fracture.
·
Mechanical properties of adhesive - fracture strength, elongation
to fracture, etc ...
·
Internal defects of the union - air bubbles, pores, delimitations,
incomplete curing of the adhesive ...
There are numerous standards which regulates and details the
conditions, tools and steps to follow for destructive testing of adhesives and
adhesive joints, the purpose of these standards is to compare and validate any
adhesive or bonding anywhere in the world.
Advantages
of destructive testing
·
Allows a roughly identify the mechanical properties of the
adhesive joint (fracture strength, elongation, modulus of elasticity ....)
·
The mechanical properties of the adhesive or adhesive bonding can
be defined according to the different types of stresses that undergo, efforts
such as tension, compression, shear, peel, dynamic forces of impact ...
·
There are many standards on destructive testing
·
The costs of equipment for destructive testing are cheaper compare
with the equipment used in nondestructive testing.
·
Ability to compare adhesives with this type of testing
·
Verification of surface preparation, curing conditions, working
conditions and adhesives system products (primers, activators, adhesives ...)
·
Predict and identify the approximate nature of the failure or
breakdown that may occur during the lifetime of the bonded joint in use, when
the specimen is previously submitted to an accelerated ageing.
·
Tests on a relatively cheaper cost.
Disadvantages
of destructive testing
·
You cannot identifies internal defectology (bubbles, delaminating,
pores, wrong thickness ...) of the real bonded joint, preventing repairs before
being put in use or during their lifetime.
·
Need to make specimens simulating the same process (surface
preparation, environmental conditions, and adhesives system products) which
cannot be reused once have been tested again.
·
Not directly identifies the status of the adhesion area in the
bonded joint.
0 komentar:
Post a Comment