Composites are materials which are mixed with one or more different and heterogeneous reinforcement. Matrix materials can generally be polymers, ceramics and metals. The matrix in the composite serves to distribute the load into all reinforcing material. Matrix properties are usually ductile. The reinforcing material in the composite has the role of holding the load received by the composite material. The nature of the reinforcing material is usually rigid and tough. Strengthening materials commonly used so far are carbon fiber, glass fiber, ceramics. The use of natural fibers as a type of fiber that has advantages began to be applied as a reinforcing material in polymer composites. This study seeks to see the effect of the use of bamboo natural fibers in polyester resin matrix on the strength of polymer composites with random and straight lengthwise fiber variations. From the tensile test results it can be seen that bamboo fibers can increase the strength of polymer composites made from polyester resin and the position of the longitudinal fibers gives a significantly more strength increase than random fibers.

The success of the welding process is the occurrence of good and strong welding joints that are inseparable from the influence of the heat source. The problem that often occurs when welding is a distortion that can trigger the initial formation of cracks. By predicting the level of welding distortion beforehand, engineers can also reduce the amount of rework by reverse design and distortion margins. That is why with current technological developments it is possible to carry out simulations based on analytical solutions that are implemented through the use of software, where in this study the authors sought to model the temperature of the HAZ region in the Butt Joint process using MSC Marc Mentat. The simulation results show that the heat source is very determining the occurrence of distortion and pressure on the surface. This is caused by the phenomenon of melting and shrinkage that occurs in a short time.