Butt joint tests

Fig. 4.11. Tensile (cylindrical) butt-joint test, (a) Unloaded, (b) Loaded, (c) Stress distribution.

Adhesion between the polymeric film and substrate is a major concern. Poor adhesion could result in flaking or peeling of the coating from the substrate core. Moisture could accmnulate at the film-substrate interface and compromise the mechanical protection provided by the coating. Polymer adhesion is related to both film-substrate interfacial interactions and internal stresses within the film. Polymer adhesion can be evaluated by peel tests or butt joint tests. Apart from the specific properties of the polymers, excipients used in tablet formulations can influence film-tablet adhesion. Since adhesion between a polymer and the tablet smface is due primarily to hydrogen bond formation, hydrophobic agents may decrease adhesion by... 

The tensile butt joint test is less commonly used as an adhesive test method this may be due to the perception that it is more difficult to prepare the test specimens ... 

Fig. 69. Adhesive stress-strain curves from BSL308A butt joint tests — specimen A -----------H-- specimen B (from Adams and Coppendale, 1979).

Fig. 81. Tensile butt joint tests (a) poker chip test (thin adhesive film) (b) and (c) schematic for thick adhesive test (d) gauge length and deflections in...

Butt-jointed test coupon to measure A strain invariant for adhesives... 

On the other hand, bulk specimens are not susceptible to the problems inherent in butt joint tests and are more suitable for providing reliable data on the response of adhesives to various known states of stress although care should be exercised in controlling the curing schedule. If a particular adhesive is not suitable for making into large bulk specimens, it should be possible to obtain uniaxial tensile stress-strain data by testing an unsupported thin film of the adhesive. 

The ASTM D 897 tensile button test is widely used to measure the tensile strength of a butt joint made with cylindrical specimens (Fig. 20.3). The tensile strength of this bond is defined as the maximum tensile load per unit area required to break the bond (measured in pounds per squre inch). The cross-sectional bond area is usually specified to be equal to 1 in.2. The specimen is loaded by means of two grips that are designed to keep the loads axially in line. The tensile test specimen requires considerable machining to ensure parallel surfaces. 

Different methods have been devised to test the bondability of the treated plastic. The specimen can be joined in different ways butt joint, disk joint, and lap shear. An adhesive layer or film is applied to the treated surface, which is then placed against the substrate and heated in a press or oven. The substrate could be a duplicate of the plastic itself. Table... 

The fracture strength of the butt joint welded by the high-current GMA welding process was studied at room and low temperatures using a deep-notch test specimen, 400 mm wide. The edge notches of the specimens were located in the weld metal or along the bond. The test results are shown in Fig. 5. For comparison, the relationship between the fracture strength and the temperature of the base metal is shown with a dashed line. 

P(5) The design of supported butt joints shall be based on testing. 

In instrumented creep tests taken to failure, one learns not only how long specimens last but also how deformation increases throughout the creep process. For lap joints, delay times have been seen in creep tests, probably due to the increasing uniformity of the shear stress state, as predicted by the shear lag model as the creep compliance of the adhesive increases with time. In other situations, no such delay time is seen. A schematic illustration of a creep curve for an adhesive bond consisting of a butt joint bonded with a pressure sensitive foam tape is shown in Fig. 2, exhibiting classical primary, secondary and tertiary regions of creep behaviour. 

Finite-element methods have also been used to evaluate new test equipment to measure shear strength under impact loads. In the equipment, two rectangular plates, bonded opposite faces of a vertical hexagonal prismatic rod, bear on a firm surface. The top of the central rod is subjected to an impact load. To prove the validity of the method, the maximum shear stress was compared with the impact shear strength, which was measured using a cylindrical butt joint subjected to impact torsional loads (see Tensile tests). 

The two main types of filled joints are butt joints and lap joints (Fig. 2) (see Shear tests and Tensile tests) each has advantages and disadvantages. The lap joint gives the sealant some protection against the weather, and a further advantage of this type of joint... 

The joint is also known as the butt joint or polker chip joint. Two solid cylinders are bonded end to end, and the joint is tested by applying a force along the common axis (Fig. 1). 

ASTM tension tests are described in ASTM D897 and D2095 and use barer rod-shaped butt joints. The maximum load at which failure occurs is recorded in pounds per square inch of bonded area. Test environment, joint geometry, and type of failure should also be recorded. 

Another tensile test, ASTM D2095-72, involves the testing of bar and rod butt joint specimens. ASTM 2094-69 describes the preparation of these specimens (see Figure 3). This test and the samples can be used with substrates comprised of metals, plastics, or reinforced plastics. Loads are applied through fixtures connected to the samples by dowel pins. The standard test rate is 2400 to 2800 lb per square inch of bond area. The maximum load at failure is used to calculate the tensile strength, the same as for the pi-tensile specimens. 

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