# Quality Analysis of Bonded Joints in the Renovation of Plastic Automotive Parts
## 2 Materials and Methods  
The test samples were taken from the front bumper of a Skoda Fabia (Skoda, Mlada Bolelav, Ceska republika), which had not been exposed to operating conditions. For the experiment, 4 mm thick polypropylene EPDM with talc additive was used and to produce the test samples, straight parts suitable for bonding were used. The mechanical properties of the selected material are shown in Table 3.  
For the bonded joints, a simple lap joint was used, as shown in Figure 1, where the overlap length was 20 \(\times\) 25 mm. According to [30], the length of the overlap splice of the bonded joint was set to 5 times the thickness of the adherend in mm. The adhesive was manually applied to the surface of the adherends, and the bonding surfaces were loaded and pressed with a 700 g weight for the curing time prescribed by the adhesive manufacturer. The principle of the joining procedure is shown in Figure 1. The same principle was used for the specimen for the tensile test. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Tensile Modulus** & **Yield Stress [MPa]** & **Brinell Hardness** & **Strain at Break** & **Charyy Notched** & **Charyy Notched** \\
**[MPa]** & **Yield Stress [MPa]** & **[MPa]** & **[\%]** & **Impact Strength** & **Impact Strength** \\  & & & & +23 \({}^{\circ}\)C [KJ/m\({}^{2}\)] & \(-\)**30 \({}^{\circ}\)C [KJ/m\({}^{2}\)]** \\ \hline
1100 & 23 & 44 & 40 & 25 & 5 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: The view of the mechanical properties of selected material PP-EPDM with talc additive. A constant adhesive thickness for the tests was provided using two distance wires of 0.1 mm diameter for each joint. The distance wires were placed at the point of contact as is shown in Figure 2. For each type of the test, 5 joints were used. The same procedure was chosen for the bonded parts to test the impact strength, as shown in Figure 3.  
Figure 1: Schematic representation of joint formation by bonding process for the Charpy impact test. (a) Distance wire insert and application of the adhesive layer, (b) application of the substrate 2, and (c) force loading of the specimens. Figure 2: The shape and dimensions of the samples for the tensile strength test. For the experiment, two types of adhesives were selected, which are used in the renovation of damaged external plastic parts of car bodies--bumpers, namely MEGABOND 2000 and DINITROL 860. The epoxy-based adhesive ChS EPOXY 1200 was used as a reference adhesive. The type of adhesive in the graphs is indicated as follows:  
* MEGABOND 200--marking M (two-component adhesive-epoxyacrylate. Curing time: 24 h at room temperature, workability up to 3 min, handling strength 4-8 min, after 60 min the surface can be ground and repainted. Temperature resistance is from \(-55\)\({}^{\circ}\)C to \(+145\)\({}^{\circ}\)C. Producer: Marstol-Domsel DmbH, Zulpich, Germany). * ChS EPOXY 1200--marking E (flexible polyurethane adhesive for plastic repairs. It is a flexible two-component cold-curing system designed primarily for bonding composites, and thermoplastics. The producer is Lugde, Germany. Curing time: 24 h at room temperature and workability up to 5 min [53]). * DINITROL 860--marking D (is a medium molecular weight epoxy adhesive modified with a plasticizer designed for bonding metals, glass, ceramics, wood, etc. Curing time: 48 h at room temperature, optimal parameters are obtained after 48 h. The curing process can be accelerated by increasing the temperature. The adhesive is perfectly mixed with the hardener in a weight ratio of 100 parts by weight of resin to 7 parts by weight of hardener). Plastic body parts are loaded in working conditions by a combination of various external factors such as external atmosphere, spreading agents, UV radiation, low temperatures, sunlight, dust gradients, rain, weather conditions, etc. [4]. Accelerated laboratory tests based on a simulation of natural and working conditions were used to investigate the change in strength properties of the evaluated joints.