ISO 14615:1997 download.Adhesives Durability of structural adhesive joints Exposure to humidity and temperature under load.
ISO 14615 describes the equipment and the test procedure used to evaluate the durability of adhesive-bonded joints exposed simultaneously to heat, humidity and load.
This method is intended for the evaluation of structural and semi-structural adhesives used in hot and/or humid environments. It is particularly suitable for metal, composite and plastic adherends.
2 Normative references
The following standards contain provisions which, through reference in this text, constitute provisions of ISO 14615. At the time of publication, the editions indicated were valid. All standards are subject to revision, and parties to agreements based on ISO 14615 are encouraged to investigate the possibility of using the most recent editions of the standards indicated below. Members of IEC and ISO maintain registers of currently valid International Standards.
ISO 4588: 1995, Adlwsives — Guidelines for the suiface preparation of metals.
The cabinet shall be such that the relative humidity can be maintained at 95% to 100% and that the temperature can be cycled between 42°C and 48°C (see 4.2). The cabinet shall be insulated and shall have an open. heated water reservoir in the base from which distilled or deionised water is pumped to spray bars at each side of the cabinet. The top of the cabinet shall have holes through which an appropriate number of specimen-loading tubes can be inserted so that they hang within 100mm of the cabinet walls.
4.2 Heater and cooling unit
The heater shall be of sufficient capacity to raise the cabinet temperature from 42°C to 48°C in 30 mm. The radiator-type cooling unit shall be of sufficient capacity to lower the cabinet temperature from 48°C to 42°C in 30 mm.
The heater and a cooling fan mounted on the radiator shall be regulated by a programmed controller linked to a temperature sensor located inside the cabinet at least 100 mm from the cabinet walls.
The controller shall he such that the temperature in the operating range is accurate to +1- 0,25°C
The heated water from the reservoir shall be circulated through the radiator into two spray bars mounted on opposite sides near the top of the cabinet (see figure 1), from where it is sprayed on to the cabinet walls.
The water level in the reservoir shall he maintained at a constant level.
Note 1: It is therefore desirable to have an automatic self-fill system and overfill alam.
Note 2: It is recommended that equipment be fitted to prevent the growth of harmful bacteria. For example. the water could be made to circulate through a UV-irradiation unit (see figure 2) consisting of two concentric tubes. The outer tube is made of UPVA or stainless steel. The inner tube consists of a short-wavelength UV source of appropriate wattage in a quartz envelope to ensure maximum penetration of the UV light. The tubes are changed at 4000 h intervals or earlier if so specified by the manufacturer.
4.4 Specimen-loading tube
The specimen-loading tube shall have a tubular main body. which contains the specimens to be tested, and a spring assembly which can be compressed and locked in place to apply the desired
damage thc jomts when the holes arc drilled. The location, size and number of drill holcs shall be either as specified or the person preparing the specimens shall ensure that drill hole location, size and number are identical for each system. In some cases. it may be desirable to drill the specimen before assembling the adherends.
The fillet area of a T-joini is particularly critical, and the shape and size of the fillet shall he checked. Consistency can he obtained by using a suitably shaped filleting tool which can be moved along the joint line after adherend assembly and before adhesive cure.
Bond thickness is usually a significant factor and shall be controlled by appropriate means such as glass spheres or spacer wires.
Note 4: Direct comparisons between different systems can he made only when specimen construction. udhcrcnd materials and test conditions tire identical.
5.3 The adherends shall he chosen from materials representative of those used in the manufacturing industry, and their thickness shall normally lie within the range 0.6mm to 3 turn.
5.4 Specimens shall be prepared individually. The lap-shear joint configuration shall he
a) either 20mm wide with a 10mm overlap (preferred)
h any other convenient width and overlap, provided that the test equipment is suitably adapted and the values are given in the test report.
5.5 The number of specimens tested in each specirnen.loading tube shall be between three and six. The number tested shall be recorded.
6 Procedure
6.1 SprinK calibration
The main and secondary springs used in the specimen-loading tube shall be calibrated on a tensile-testing machine and individually numbered. A calibration chart shall be prepared for each main spring, relating the applied load to the distance separating the middle and bottom spring housings. It is preferable to maintain particular spring and tube combinations.
The secondary spring shall be chosen such that, when fully compressed in the lop spring housing. it applies a load of I MPa.
6.2 Assernbh
Assemble a series of at least three suitable specimens by bolting them together with stainless- steel or polyamide bolts Use solid strips of material to complete the series if necessary.
Insert the series into the specimen-loading tube by sccurcly pinning ii first to the the bottom of the spring shaft. With the bottom spring housing and washer in position on the shaft, slide the specimens into the specimen-loading tube, Secure the bottom spring housing to the tube using the attachment screws, which prevent the speci.nen.% from twisting when they are under load. Place the end-cap over the end of the series of specimens and securely pin.
Locate the main spring over the shaft and then the middle spring housing. Place the sccondary spring and its housing over the shaft and Imally the washer and nut.
With the tube held firmly in a vice, turn the nut until the top spring housing is just tight. Using an interior calliper and a micrometer. take a reading of the spacing between the middle and bottom spring housings and record. Consult the spring calibration chart and, using the chart and the reading obtained, set the callipcn for the spacing required at the desired load. Tighten the nut on the spring shaft until the calliper is just tight,
6.3 Introducing the tubes into the cabinet
Introduce the specimen-loading tubes through the holes in the Lop of the cabinet so that they hang vertically. Seal any unused holes in the top of the cabinet and any gaps between the tubes and the cabinet top.
6.4 Temperature cscle
unless another temperature cycle is specified by the refeuing standani. selected for instance
from those ckfined in ISO 9142, the cabinet temperature shall be continuously cycled between
42°C and 48°C, taking 60 mm i-I- 5 mm to complete a full cycle from 42°C to 41°C and back to
42°C.
6.5 Testing
Record the date and time of the start of the test.
Continue the lest until a joint fails and record the time to failure. Check the tubes daily. or at shorter periods if appropriate (the spring assembly will be loose when a joint has failed).
When a failure occurs, disassemble the tube and replace the failed specimen with a solid stnp of appropriate length. Re-assemble the tube and place under load as before. Introduce the tube into the cabinet again and record the time to failure of the next joinL Continue this procedure until at least three of the joints in the series have failed.
Record the failure pattern in accordance with ISO 10365.
Record the load applied.
Note 5: Control specimens may be included in any comparative investigation, at the discretion of the individual user.
Note 6: The ereep/relasation history of the individual specimens will be different. owing to the replacement of the failed specimens and reloading of the remaining ones. However, since the test may last several weeks, the effect of relaxation is not significant.